ZFS: MFV 2.0-rc1-ga00c61

[FreeBSD/FreeBSD.git] / sys / kern / vfs_vnops.c

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1982, 1986, 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Copyright (c) 2012 Konstantin Belousov <kib@FreeBSD.org>
 * Copyright (c) 2013, 2014 The FreeBSD Foundation
 *
 * Portions of this software were developed by Konstantin Belousov
 * under sponsorship from the FreeBSD Foundation.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)vfs_vnops.c 8.2 (Berkeley) 1/21/94
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_hwpmc_hooks.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/disk.h>
#include <sys/fail.h>
#include <sys/fcntl.h>
#include <sys/file.h>
#include <sys/kdb.h>
#include <sys/ktr.h>
#include <sys/stat.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/mutex.h>
#include <sys/namei.h>
#include <sys/vnode.h>
#include <sys/bio.h>
#include <sys/buf.h>
#include <sys/filio.h>
#include <sys/resourcevar.h>
#include <sys/rwlock.h>
#include <sys/sx.h>
#include <sys/sleepqueue.h>
#include <sys/sysctl.h>
#include <sys/ttycom.h>
#include <sys/conf.h>
#include <sys/syslog.h>
#include <sys/unistd.h>
#include <sys/user.h>

#include <security/audit/audit.h>
#include <security/mac/mac_framework.h>

#include <vm/vm.h>
#include <vm/vm_extern.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pager.h>

#ifdef HWPMC_HOOKS
#include <sys/pmckern.h>
#endif

static fo_rdwr_t        vn_read;
static fo_rdwr_t        vn_write;
static fo_rdwr_t        vn_io_fault;
static fo_truncate_t    vn_truncate;
static fo_ioctl_t       vn_ioctl;
static fo_poll_t        vn_poll;
static fo_kqfilter_t    vn_kqfilter;
static fo_stat_t        vn_statfile;
static fo_close_t       vn_closefile;
static fo_mmap_t        vn_mmap;
static fo_fallocate_t   vn_fallocate;

struct  fileops vnops = {
        .fo_read = vn_io_fault,
        .fo_write = vn_io_fault,
        .fo_truncate = vn_truncate,
        .fo_ioctl = vn_ioctl,
        .fo_poll = vn_poll,
        .fo_kqfilter = vn_kqfilter,
        .fo_stat = vn_statfile,
        .fo_close = vn_closefile,
        .fo_chmod = vn_chmod,
        .fo_chown = vn_chown,
        .fo_sendfile = vn_sendfile,
        .fo_seek = vn_seek,
        .fo_fill_kinfo = vn_fill_kinfo,
        .fo_mmap = vn_mmap,
        .fo_fallocate = vn_fallocate,
        .fo_flags = DFLAG_PASSABLE | DFLAG_SEEKABLE
};

static const int io_hold_cnt = 16;
static int vn_io_fault_enable = 1;
SYSCTL_INT(_debug, OID_AUTO, vn_io_fault_enable, CTLFLAG_RWTUN,
    &vn_io_fault_enable, 0, "Enable vn_io_fault lock avoidance");
static int vn_io_fault_prefault = 0;
SYSCTL_INT(_debug, OID_AUTO, vn_io_fault_prefault, CTLFLAG_RWTUN,
    &vn_io_fault_prefault, 0, "Enable vn_io_fault prefaulting");
static int vn_io_pgcache_read_enable = 1;
SYSCTL_INT(_debug, OID_AUTO, vn_io_pgcache_read_enable, CTLFLAG_RWTUN,
    &vn_io_pgcache_read_enable, 0,
    "Enable copying from page cache for reads, avoiding fs");
static u_long vn_io_faults_cnt;
SYSCTL_ULONG(_debug, OID_AUTO, vn_io_faults, CTLFLAG_RD,
    &vn_io_faults_cnt, 0, "Count of vn_io_fault lock avoidance triggers");

static int vfs_allow_read_dir = 0;
SYSCTL_INT(_security_bsd, OID_AUTO, allow_read_dir, CTLFLAG_RW,
    &vfs_allow_read_dir, 0,
    "Enable read(2) of directory by root for filesystems that support it");

/*
 * Returns true if vn_io_fault mode of handling the i/o request should
 * be used.
 */
static bool
do_vn_io_fault(struct vnode *vp, struct uio *uio)
{
        struct mount *mp;

        return (uio->uio_segflg == UIO_USERSPACE && vp->v_type == VREG &&
            (mp = vp->v_mount) != NULL &&
            (mp->mnt_kern_flag & MNTK_NO_IOPF) != 0 && vn_io_fault_enable);
}

/*
 * Structure used to pass arguments to vn_io_fault1(), to do either
 * file- or vnode-based I/O calls.
 */
struct vn_io_fault_args {
        enum {
                VN_IO_FAULT_FOP,
                VN_IO_FAULT_VOP
        } kind;
        struct ucred *cred;
        int flags;
        union {
                struct fop_args_tag {
                        struct file *fp;
                        fo_rdwr_t *doio;
                } fop_args;
                struct vop_args_tag {
                        struct vnode *vp;
                } vop_args;
        } args;
};

static int vn_io_fault1(struct vnode *vp, struct uio *uio,
    struct vn_io_fault_args *args, struct thread *td);

int
vn_open(struct nameidata *ndp, int *flagp, int cmode, struct file *fp)
{
        struct thread *td = ndp->ni_cnd.cn_thread;

        return (vn_open_cred(ndp, flagp, cmode, 0, td->td_ucred, fp));
}

/*
 * Common code for vnode open operations via a name lookup.
 * Lookup the vnode and invoke VOP_CREATE if needed.
 * Check permissions, and call the VOP_OPEN or VOP_CREATE routine.
 *
 * Note that this does NOT free nameidata for the successful case,
 * due to the NDINIT being done elsewhere.
 */
int
vn_open_cred(struct nameidata *ndp, int *flagp, int cmode, u_int vn_open_flags,
    struct ucred *cred, struct file *fp)
{
        struct vnode *vp;
        struct mount *mp;
        struct thread *td = ndp->ni_cnd.cn_thread;
        struct vattr vat;
        struct vattr *vap = &vat;
        int fmode, error;

restart:
        fmode = *flagp;
        if ((fmode & (O_CREAT | O_EXCL | O_DIRECTORY)) == (O_CREAT |
            O_EXCL | O_DIRECTORY))
                return (EINVAL);
        else if ((fmode & (O_CREAT | O_DIRECTORY)) == O_CREAT) {
                ndp->ni_cnd.cn_nameiop = CREATE;
                /*
                 * Set NOCACHE to avoid flushing the cache when
                 * rolling in many files at once.
                */
                ndp->ni_cnd.cn_flags = ISOPEN | LOCKPARENT | LOCKLEAF | NOCACHE;
                if ((fmode & O_EXCL) == 0 && (fmode & O_NOFOLLOW) == 0)
                        ndp->ni_cnd.cn_flags |= FOLLOW;
                if ((fmode & O_BENEATH) != 0)
                        ndp->ni_cnd.cn_flags |= BENEATH;
                if (!(vn_open_flags & VN_OPEN_NOAUDIT))
                        ndp->ni_cnd.cn_flags |= AUDITVNODE1;
                if (vn_open_flags & VN_OPEN_NOCAPCHECK)
                        ndp->ni_cnd.cn_flags |= NOCAPCHECK;
                if ((vn_open_flags & VN_OPEN_INVFS) == 0)
                        bwillwrite();
                if ((error = namei(ndp)) != 0)
                        return (error);
                if (ndp->ni_vp == NULL) {
                        VATTR_NULL(vap);
                        vap->va_type = VREG;
                        vap->va_mode = cmode;
                        if (fmode & O_EXCL)
                                vap->va_vaflags |= VA_EXCLUSIVE;
                        if (vn_start_write(ndp->ni_dvp, &mp, V_NOWAIT) != 0) {
                                NDFREE(ndp, NDF_ONLY_PNBUF);
                                vput(ndp->ni_dvp);
                                if ((error = vn_start_write(NULL, &mp,
                                    V_XSLEEP | PCATCH)) != 0)
                                        return (error);
                                goto restart;
                        }
                        if ((vn_open_flags & VN_OPEN_NAMECACHE) != 0)
                                ndp->ni_cnd.cn_flags |= MAKEENTRY;
#ifdef MAC
                        error = mac_vnode_check_create(cred, ndp->ni_dvp,
                            &ndp->ni_cnd, vap);
                        if (error == 0)
#endif
                                error = VOP_CREATE(ndp->ni_dvp, &ndp->ni_vp,
                                                   &ndp->ni_cnd, vap);
                        vput(ndp->ni_dvp);
                        vn_finished_write(mp);
                        if (error) {
                                NDFREE(ndp, NDF_ONLY_PNBUF);
                                return (error);
                        }
                        fmode &= ~O_TRUNC;
                        vp = ndp->ni_vp;
                } else {
                        if (ndp->ni_dvp == ndp->ni_vp)
                                vrele(ndp->ni_dvp);
                        else
                                vput(ndp->ni_dvp);
                        ndp->ni_dvp = NULL;
                        vp = ndp->ni_vp;
                        if (fmode & O_EXCL) {
                                error = EEXIST;
                                goto bad;
                        }
                        if (vp->v_type == VDIR) {
                                error = EISDIR;
                                goto bad;
                        }
                        fmode &= ~O_CREAT;
                }
        } else {
                ndp->ni_cnd.cn_nameiop = LOOKUP;
                ndp->ni_cnd.cn_flags = ISOPEN |
                    ((fmode & O_NOFOLLOW) ? NOFOLLOW : FOLLOW) | LOCKLEAF;
                if (!(fmode & FWRITE))
                        ndp->ni_cnd.cn_flags |= LOCKSHARED;
                if ((fmode & O_BENEATH) != 0)
                        ndp->ni_cnd.cn_flags |= BENEATH;
                if (!(vn_open_flags & VN_OPEN_NOAUDIT))
                        ndp->ni_cnd.cn_flags |= AUDITVNODE1;
                if (vn_open_flags & VN_OPEN_NOCAPCHECK)
                        ndp->ni_cnd.cn_flags |= NOCAPCHECK;
                if ((error = namei(ndp)) != 0)
                        return (error);
                vp = ndp->ni_vp;
        }
        error = vn_open_vnode(vp, fmode, cred, td, fp);
        if (error)
                goto bad;
        *flagp = fmode;
        return (0);
bad:
        NDFREE(ndp, NDF_ONLY_PNBUF);
        vput(vp);
        *flagp = fmode;
        ndp->ni_vp = NULL;
        return (error);
}

static int
vn_open_vnode_advlock(struct vnode *vp, int fmode, struct file *fp)
{
        struct flock lf;
        int error, lock_flags, type;

        ASSERT_VOP_LOCKED(vp, "vn_open_vnode_advlock");
        if ((fmode & (O_EXLOCK | O_SHLOCK)) == 0)
                return (0);
        KASSERT(fp != NULL, ("open with flock requires fp"));
        if (fp->f_type != DTYPE_NONE && fp->f_type != DTYPE_VNODE)
                return (EOPNOTSUPP);

        lock_flags = VOP_ISLOCKED(vp);
        VOP_UNLOCK(vp);

        lf.l_whence = SEEK_SET;
        lf.l_start = 0;
        lf.l_len = 0;
        lf.l_type = (fmode & O_EXLOCK) != 0 ? F_WRLCK : F_RDLCK;
        type = F_FLOCK;
        if ((fmode & FNONBLOCK) == 0)
                type |= F_WAIT;
        error = VOP_ADVLOCK(vp, (caddr_t)fp, F_SETLK, &lf, type);
        if (error == 0)
                fp->f_flag |= FHASLOCK;

        vn_lock(vp, lock_flags | LK_RETRY);
        if (error == 0 && VN_IS_DOOMED(vp))
                error = ENOENT;
        return (error);
}

/*
 * Common code for vnode open operations once a vnode is located.
 * Check permissions, and call the VOP_OPEN routine.
 */
int
vn_open_vnode(struct vnode *vp, int fmode, struct ucred *cred,
    struct thread *td, struct file *fp)
{
        accmode_t accmode;
        int error;

        if (vp->v_type == VLNK)
                return (EMLINK);
        if (vp->v_type == VSOCK)
                return (EOPNOTSUPP);
        if (vp->v_type != VDIR && fmode & O_DIRECTORY)
                return (ENOTDIR);
        accmode = 0;
        if (fmode & (FWRITE | O_TRUNC)) {
                if (vp->v_type == VDIR)
                        return (EISDIR);
                accmode |= VWRITE;
        }
        if (fmode & FREAD)
                accmode |= VREAD;
        if (fmode & FEXEC)
                accmode |= VEXEC;
        if ((fmode & O_APPEND) && (fmode & FWRITE))
                accmode |= VAPPEND;
#ifdef MAC
        if (fmode & O_CREAT)
                accmode |= VCREAT;
        if (fmode & O_VERIFY)
                accmode |= VVERIFY;
        error = mac_vnode_check_open(cred, vp, accmode);
        if (error)
                return (error);

        accmode &= ~(VCREAT | VVERIFY);
#endif
        if ((fmode & O_CREAT) == 0 && accmode != 0) {
                error = VOP_ACCESS(vp, accmode, cred, td);
                if (error != 0)
                        return (error);
        }
        if (vp->v_type == VFIFO && VOP_ISLOCKED(vp) != LK_EXCLUSIVE)
                vn_lock(vp, LK_UPGRADE | LK_RETRY);
        error = VOP_OPEN(vp, fmode, cred, td, fp);
        if (error != 0)
                return (error);

        error = vn_open_vnode_advlock(vp, fmode, fp);
        if (error == 0 && (fmode & FWRITE) != 0) {
                error = VOP_ADD_WRITECOUNT(vp, 1);
                if (error == 0) {
                        CTR3(KTR_VFS, "%s: vp %p v_writecount increased to %d",
                             __func__, vp, vp->v_writecount);
                }
        }

        /*
         * Error from advlock or VOP_ADD_WRITECOUNT() still requires
         * calling VOP_CLOSE() to pair with earlier VOP_OPEN().
         * Arrange for that by having fdrop() to use vn_closefile().
         */
        if (error != 0) {
                fp->f_flag |= FOPENFAILED;
                fp->f_vnode = vp;
                if (fp->f_ops == &badfileops) {
                        fp->f_type = DTYPE_VNODE;
                        fp->f_ops = &vnops;
                }
                vref(vp);
        }

        ASSERT_VOP_LOCKED(vp, "vn_open_vnode");
        return (error);

}

/*
 * Check for write permissions on the specified vnode.
 * Prototype text segments cannot be written.
 * It is racy.
 */
int
vn_writechk(struct vnode *vp)
{

        ASSERT_VOP_LOCKED(vp, "vn_writechk");
        /*
         * If there's shared text associated with
         * the vnode, try to free it up once.  If
         * we fail, we can't allow writing.
         */
        if (VOP_IS_TEXT(vp))
                return (ETXTBSY);

        return (0);
}

/*
 * Vnode close call
 */
static int
vn_close1(struct vnode *vp, int flags, struct ucred *file_cred,
    struct thread *td, bool keep_ref)
{
        struct mount *mp;
        int error, lock_flags;

        if (vp->v_type != VFIFO && (flags & FWRITE) == 0 &&
            MNT_EXTENDED_SHARED(vp->v_mount))
                lock_flags = LK_SHARED;
        else
                lock_flags = LK_EXCLUSIVE;

        vn_start_write(vp, &mp, V_WAIT);
        vn_lock(vp, lock_flags | LK_RETRY);
        AUDIT_ARG_VNODE1(vp);
        if ((flags & (FWRITE | FOPENFAILED)) == FWRITE) {
                VOP_ADD_WRITECOUNT_CHECKED(vp, -1);
                CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d",
                    __func__, vp, vp->v_writecount);
        }
        error = VOP_CLOSE(vp, flags, file_cred, td);
        if (keep_ref)
                VOP_UNLOCK(vp);
        else
                vput(vp);
        vn_finished_write(mp);
        return (error);
}

int
vn_close(struct vnode *vp, int flags, struct ucred *file_cred,
    struct thread *td)
{

        return (vn_close1(vp, flags, file_cred, td, false));
}

/*
 * Heuristic to detect sequential operation.
 */
static int
sequential_heuristic(struct uio *uio, struct file *fp)
{
        enum uio_rw rw;

        ASSERT_VOP_LOCKED(fp->f_vnode, __func__);

        rw = uio->uio_rw;
        if (fp->f_flag & FRDAHEAD)
                return (fp->f_seqcount[rw] << IO_SEQSHIFT);

        /*
         * Offset 0 is handled specially.  open() sets f_seqcount to 1 so
         * that the first I/O is normally considered to be slightly
         * sequential.  Seeking to offset 0 doesn't change sequentiality
         * unless previous seeks have reduced f_seqcount to 0, in which
         * case offset 0 is not special.
         */
        if ((uio->uio_offset == 0 && fp->f_seqcount[rw] > 0) ||
            uio->uio_offset == fp->f_nextoff[rw]) {
                /*
                 * f_seqcount is in units of fixed-size blocks so that it
                 * depends mainly on the amount of sequential I/O and not
                 * much on the number of sequential I/O's.  The fixed size
                 * of 16384 is hard-coded here since it is (not quite) just
                 * a magic size that works well here.  This size is more
                 * closely related to the best I/O size for real disks than
                 * to any block size used by software.
                 */
                if (uio->uio_resid >= IO_SEQMAX * 16384)
                        fp->f_seqcount[rw] = IO_SEQMAX;
                else {
                        fp->f_seqcount[rw] += howmany(uio->uio_resid, 16384);
                        if (fp->f_seqcount[rw] > IO_SEQMAX)
                                fp->f_seqcount[rw] = IO_SEQMAX;
                }
                return (fp->f_seqcount[rw] << IO_SEQSHIFT);
        }

        /* Not sequential.  Quickly draw-down sequentiality. */
        if (fp->f_seqcount[rw] > 1)
                fp->f_seqcount[rw] = 1;
        else
                fp->f_seqcount[rw] = 0;
        return (0);
}

/*
 * Package up an I/O request on a vnode into a uio and do it.
 */
int
vn_rdwr(enum uio_rw rw, struct vnode *vp, void *base, int len, off_t offset,
    enum uio_seg segflg, int ioflg, struct ucred *active_cred,
    struct ucred *file_cred, ssize_t *aresid, struct thread *td)
{
        struct uio auio;
        struct iovec aiov;
        struct mount *mp;
        struct ucred *cred;
        void *rl_cookie;
        struct vn_io_fault_args args;
        int error, lock_flags;

        if (offset < 0 && vp->v_type != VCHR)
                return (EINVAL);
        auio.uio_iov = &aiov;
        auio.uio_iovcnt = 1;
        aiov.iov_base = base;
        aiov.iov_len = len;
        auio.uio_resid = len;
        auio.uio_offset = offset;
        auio.uio_segflg = segflg;
        auio.uio_rw = rw;
        auio.uio_td = td;
        error = 0;

        if ((ioflg & IO_NODELOCKED) == 0) {
                if ((ioflg & IO_RANGELOCKED) == 0) {
                        if (rw == UIO_READ) {
                                rl_cookie = vn_rangelock_rlock(vp, offset,
                                    offset + len);
                        } else {
                                rl_cookie = vn_rangelock_wlock(vp, offset,
                                    offset + len);
                        }
                } else
                        rl_cookie = NULL;
                mp = NULL;
                if (rw == UIO_WRITE) { 
                        if (vp->v_type != VCHR &&
                            (error = vn_start_write(vp, &mp, V_WAIT | PCATCH))
                            != 0)
                                goto out;
                        if (MNT_SHARED_WRITES(mp) ||
                            ((mp == NULL) && MNT_SHARED_WRITES(vp->v_mount)))
                                lock_flags = LK_SHARED;
                        else
                                lock_flags = LK_EXCLUSIVE;
                } else
                        lock_flags = LK_SHARED;
                vn_lock(vp, lock_flags | LK_RETRY);
        } else
                rl_cookie = NULL;

        ASSERT_VOP_LOCKED(vp, "IO_NODELOCKED with no vp lock held");
#ifdef MAC
        if ((ioflg & IO_NOMACCHECK) == 0) {
                if (rw == UIO_READ)
                        error = mac_vnode_check_read(active_cred, file_cred,
                            vp);
                else
                        error = mac_vnode_check_write(active_cred, file_cred,
                            vp);
        }
#endif
        if (error == 0) {
                if (file_cred != NULL)
                        cred = file_cred;
                else
                        cred = active_cred;
                if (do_vn_io_fault(vp, &auio)) {
                        args.kind = VN_IO_FAULT_VOP;
                        args.cred = cred;
                        args.flags = ioflg;
                        args.args.vop_args.vp = vp;
                        error = vn_io_fault1(vp, &auio, &args, td);
                } else if (rw == UIO_READ) {
                        error = VOP_READ(vp, &auio, ioflg, cred);
                } else /* if (rw == UIO_WRITE) */ {
                        error = VOP_WRITE(vp, &auio, ioflg, cred);
                }
        }
        if (aresid)
                *aresid = auio.uio_resid;
        else
                if (auio.uio_resid && error == 0)
                        error = EIO;
        if ((ioflg & IO_NODELOCKED) == 0) {
                VOP_UNLOCK(vp);
                if (mp != NULL)
                        vn_finished_write(mp);
        }
 out:
        if (rl_cookie != NULL)
                vn_rangelock_unlock(vp, rl_cookie);
        return (error);
}

/*
 * Package up an I/O request on a vnode into a uio and do it.  The I/O
 * request is split up into smaller chunks and we try to avoid saturating
 * the buffer cache while potentially holding a vnode locked, so we 
 * check bwillwrite() before calling vn_rdwr().  We also call kern_yield()
 * to give other processes a chance to lock the vnode (either other processes
 * core'ing the same binary, or unrelated processes scanning the directory).
 */
int
vn_rdwr_inchunks(enum uio_rw rw, struct vnode *vp, void *base, size_t len,
    off_t offset, enum uio_seg segflg, int ioflg, struct ucred *active_cred,
    struct ucred *file_cred, size_t *aresid, struct thread *td)
{
        int error = 0;
        ssize_t iaresid;

        do {
                int chunk;

                /*
                 * Force `offset' to a multiple of MAXBSIZE except possibly
                 * for the first chunk, so that filesystems only need to
                 * write full blocks except possibly for the first and last
                 * chunks.
                 */
                chunk = MAXBSIZE - (uoff_t)offset % MAXBSIZE;

                if (chunk > len)
                        chunk = len;
                if (rw != UIO_READ && vp->v_type == VREG)
                        bwillwrite();
                iaresid = 0;
                error = vn_rdwr(rw, vp, base, chunk, offset, segflg,
                    ioflg, active_cred, file_cred, &iaresid, td);
                len -= chunk;   /* aresid calc already includes length */
                if (error)
                        break;
                offset += chunk;
                base = (char *)base + chunk;
                kern_yield(PRI_USER);
        } while (len);
        if (aresid)
                *aresid = len + iaresid;
        return (error);
}

#if OFF_MAX <= LONG_MAX
off_t
foffset_lock(struct file *fp, int flags)
{
        volatile short *flagsp;
        off_t res;
        short state;

        KASSERT((flags & FOF_OFFSET) == 0, ("FOF_OFFSET passed"));

        if ((flags & FOF_NOLOCK) != 0)
                return (atomic_load_long(&fp->f_offset));

        /*
         * According to McKusick the vn lock was protecting f_offset here.
         * It is now protected by the FOFFSET_LOCKED flag.
         */
        flagsp = &fp->f_vnread_flags;
        if (atomic_cmpset_acq_16(flagsp, 0, FOFFSET_LOCKED))
                return (atomic_load_long(&fp->f_offset));

        sleepq_lock(&fp->f_vnread_flags);
        state = atomic_load_16(flagsp);
        for (;;) {
                if ((state & FOFFSET_LOCKED) == 0) {
                        if (!atomic_fcmpset_acq_16(flagsp, &state,
                            FOFFSET_LOCKED))
                                continue;
                        break;
                }
                if ((state & FOFFSET_LOCK_WAITING) == 0) {
                        if (!atomic_fcmpset_acq_16(flagsp, &state,
                            state | FOFFSET_LOCK_WAITING))
                                continue;
                }
                DROP_GIANT();
                sleepq_add(&fp->f_vnread_flags, NULL, "vofflock", 0, 0);
                sleepq_wait(&fp->f_vnread_flags, PUSER -1);
                PICKUP_GIANT();
                sleepq_lock(&fp->f_vnread_flags);
                state = atomic_load_16(flagsp);
        }
        res = atomic_load_long(&fp->f_offset);
        sleepq_release(&fp->f_vnread_flags);
        return (res);
}

void
foffset_unlock(struct file *fp, off_t val, int flags)
{
        volatile short *flagsp;
        short state;

        KASSERT((flags & FOF_OFFSET) == 0, ("FOF_OFFSET passed"));

        if ((flags & FOF_NOUPDATE) == 0)
                atomic_store_long(&fp->f_offset, val);
        if ((flags & FOF_NEXTOFF_R) != 0)
                fp->f_nextoff[UIO_READ] = val;
        if ((flags & FOF_NEXTOFF_W) != 0)
                fp->f_nextoff[UIO_WRITE] = val;

        if ((flags & FOF_NOLOCK) != 0)
                return;

        flagsp = &fp->f_vnread_flags;
        state = atomic_load_16(flagsp);
        if ((state & FOFFSET_LOCK_WAITING) == 0 &&
            atomic_cmpset_rel_16(flagsp, state, 0))
                return;

        sleepq_lock(&fp->f_vnread_flags);
        MPASS((fp->f_vnread_flags & FOFFSET_LOCKED) != 0);
        MPASS((fp->f_vnread_flags & FOFFSET_LOCK_WAITING) != 0);
        fp->f_vnread_flags = 0;
        sleepq_broadcast(&fp->f_vnread_flags, SLEEPQ_SLEEP, 0, 0);
        sleepq_release(&fp->f_vnread_flags);
}
#else
off_t
foffset_lock(struct file *fp, int flags)
{
        struct mtx *mtxp;
        off_t res;

        KASSERT((flags & FOF_OFFSET) == 0, ("FOF_OFFSET passed"));

        mtxp = mtx_pool_find(mtxpool_sleep, fp);
        mtx_lock(mtxp);
        if ((flags & FOF_NOLOCK) == 0) {
                while (fp->f_vnread_flags & FOFFSET_LOCKED) {
                        fp->f_vnread_flags |= FOFFSET_LOCK_WAITING;
                        msleep(&fp->f_vnread_flags, mtxp, PUSER -1,
                            "vofflock", 0);
                }
                fp->f_vnread_flags |= FOFFSET_LOCKED;
        }
        res = fp->f_offset;
        mtx_unlock(mtxp);
        return (res);
}

void
foffset_unlock(struct file *fp, off_t val, int flags)
{
        struct mtx *mtxp;

        KASSERT((flags & FOF_OFFSET) == 0, ("FOF_OFFSET passed"));

        mtxp = mtx_pool_find(mtxpool_sleep, fp);
        mtx_lock(mtxp);
        if ((flags & FOF_NOUPDATE) == 0)
                fp->f_offset = val;
        if ((flags & FOF_NEXTOFF_R) != 0)
                fp->f_nextoff[UIO_READ] = val;
        if ((flags & FOF_NEXTOFF_W) != 0)
                fp->f_nextoff[UIO_WRITE] = val;
        if ((flags & FOF_NOLOCK) == 0) {
                KASSERT((fp->f_vnread_flags & FOFFSET_LOCKED) != 0,
                    ("Lost FOFFSET_LOCKED"));
                if (fp->f_vnread_flags & FOFFSET_LOCK_WAITING)
                        wakeup(&fp->f_vnread_flags);
                fp->f_vnread_flags = 0;
        }
        mtx_unlock(mtxp);
}
#endif

void
foffset_lock_uio(struct file *fp, struct uio *uio, int flags)
{

        if ((flags & FOF_OFFSET) == 0)
                uio->uio_offset = foffset_lock(fp, flags);
}

void
foffset_unlock_uio(struct file *fp, struct uio *uio, int flags)
{

        if ((flags & FOF_OFFSET) == 0)
                foffset_unlock(fp, uio->uio_offset, flags);
}

static int
get_advice(struct file *fp, struct uio *uio)
{
        struct mtx *mtxp;
        int ret;

        ret = POSIX_FADV_NORMAL;
        if (fp->f_advice == NULL || fp->f_vnode->v_type != VREG)
                return (ret);

        mtxp = mtx_pool_find(mtxpool_sleep, fp);
        mtx_lock(mtxp);
        if (fp->f_advice != NULL &&
            uio->uio_offset >= fp->f_advice->fa_start &&
            uio->uio_offset + uio->uio_resid <= fp->f_advice->fa_end)
                ret = fp->f_advice->fa_advice;
        mtx_unlock(mtxp);
        return (ret);
}

static int
vn_read_from_obj(struct vnode *vp, struct uio *uio)
{
        vm_object_t obj;
        vm_page_t ma[io_hold_cnt + 2];
        off_t off, vsz;
        ssize_t resid;
        int error, i, j;

        obj = vp->v_object;
        MPASS(uio->uio_resid <= ptoa(io_hold_cnt + 2));
        MPASS(obj != NULL);
        MPASS(obj->type == OBJT_VNODE);

        /*
         * Depends on type stability of vm_objects.
         */
        vm_object_pip_add(obj, 1);
        if ((obj->flags & OBJ_DEAD) != 0) {
                /*
                 * Note that object might be already reused from the
                 * vnode, and the OBJ_DEAD flag cleared.  This is fine,
                 * we recheck for DOOMED vnode state after all pages
                 * are busied, and retract then.
                 *
                 * But we check for OBJ_DEAD to ensure that we do not
                 * busy pages while vm_object_terminate_pages()
                 * processes the queue.
                 */
                error = EJUSTRETURN;
                goto out_pip;
        }

        resid = uio->uio_resid;
        off = uio->uio_offset;
        for (i = 0; resid > 0; i++) {
                MPASS(i < io_hold_cnt + 2);
                ma[i] = vm_page_grab_unlocked(obj, atop(off),
                    VM_ALLOC_NOCREAT | VM_ALLOC_SBUSY | VM_ALLOC_IGN_SBUSY |
                    VM_ALLOC_NOWAIT);
                if (ma[i] == NULL)
                        break;

                /*
                 * Skip invalid pages.  Valid mask can be partial only
                 * at EOF, and we clip later.
                 */
                if (vm_page_none_valid(ma[i])) {
                        vm_page_sunbusy(ma[i]);
                        break;
                }

                resid -= PAGE_SIZE;
                off += PAGE_SIZE;
        }
        if (i == 0) {
                error = EJUSTRETURN;
                goto out_pip;
        }

        /*
         * Check VIRF_DOOMED after we busied our pages.  Since
         * vgonel() terminates the vnode' vm_object, it cannot
         * process past pages busied by us.
         */
        if (VN_IS_DOOMED(vp)) {
                error = EJUSTRETURN;
                goto out;
        }

        resid = PAGE_SIZE - (uio->uio_offset & PAGE_MASK) + ptoa(i - 1);
        if (resid > uio->uio_resid)
                resid = uio->uio_resid;

        /*
         * Unlocked read of vnp_size is safe because truncation cannot
         * pass busied page.  But we load vnp_size into a local
         * variable so that possible concurrent extension does not
         * break calculation.
         */
#if defined(__powerpc__) && !defined(__powerpc64__)
        vsz = obj->un_pager.vnp.vnp_size;
#else
        vsz = atomic_load_64(&obj->un_pager.vnp.vnp_size);
#endif
        if (uio->uio_offset + resid > vsz)
                resid = vsz - uio->uio_offset;

        error = vn_io_fault_pgmove(ma, uio->uio_offset & PAGE_MASK, resid, uio);

out:
        for (j = 0; j < i; j++) {
                if (error == 0)
                        vm_page_reference(ma[j]);
                vm_page_sunbusy(ma[j]);
        }
out_pip:
        vm_object_pip_wakeup(obj);
        if (error != 0)
                return (error);
        return (uio->uio_resid == 0 ? 0 : EJUSTRETURN);
}

static bool
do_vn_read_from_pgcache(struct vnode *vp, struct uio *uio, struct file *fp)
{
        return ((vp->v_irflag & (VIRF_DOOMED | VIRF_PGREAD)) == VIRF_PGREAD &&
            !mac_vnode_check_read_enabled() &&
            uio->uio_resid <= ptoa(io_hold_cnt) && uio->uio_offset >= 0 &&
            (fp->f_flag & O_DIRECT) == 0 && vn_io_pgcache_read_enable);
}

/*
 * File table vnode read routine.
 */
static int
vn_read(struct file *fp, struct uio *uio, struct ucred *active_cred, int flags,
    struct thread *td)
{
        struct vnode *vp;
        off_t orig_offset;
        int error, ioflag;
        int advice;

        KASSERT(uio->uio_td == td, ("uio_td %p is not td %p",
            uio->uio_td, td));
        KASSERT(flags & FOF_OFFSET, ("No FOF_OFFSET"));
        vp = fp->f_vnode;
        if (do_vn_read_from_pgcache(vp, uio, fp)) {
                error = vn_read_from_obj(vp, uio);
                if (error == 0) {
                        fp->f_nextoff[UIO_READ] = uio->uio_offset;
                        return (0);
                }
                if (error != EJUSTRETURN)
                        return (error);
        }
        ioflag = 0;
        if (fp->f_flag & FNONBLOCK)
                ioflag |= IO_NDELAY;
        if (fp->f_flag & O_DIRECT)
                ioflag |= IO_DIRECT;
        advice = get_advice(fp, uio);
        vn_lock(vp, LK_SHARED | LK_RETRY);

        switch (advice) {
        case POSIX_FADV_NORMAL:
        case POSIX_FADV_SEQUENTIAL:
        case POSIX_FADV_NOREUSE:
                ioflag |= sequential_heuristic(uio, fp);
                break;
        case POSIX_FADV_RANDOM:
                /* Disable read-ahead for random I/O. */
                break;
        }
        orig_offset = uio->uio_offset;

#ifdef MAC
        error = mac_vnode_check_read(active_cred, fp->f_cred, vp);
        if (error == 0)
#endif
                error = VOP_READ(vp, uio, ioflag, fp->f_cred);
        fp->f_nextoff[UIO_READ] = uio->uio_offset;
        VOP_UNLOCK(vp);
        if (error == 0 && advice == POSIX_FADV_NOREUSE &&
            orig_offset != uio->uio_offset)
                /*
                 * Use POSIX_FADV_DONTNEED to flush pages and buffers
                 * for the backing file after a POSIX_FADV_NOREUSE
                 * read(2).
                 */
                error = VOP_ADVISE(vp, orig_offset, uio->uio_offset - 1,
                    POSIX_FADV_DONTNEED);
        return (error);
}

/*
 * File table vnode write routine.
 */
static int
vn_write(struct file *fp, struct uio *uio, struct ucred *active_cred, int flags,
    struct thread *td)
{
        struct vnode *vp;
        struct mount *mp;
        off_t orig_offset;
        int error, ioflag, lock_flags;
        int advice;

        KASSERT(uio->uio_td == td, ("uio_td %p is not td %p",
            uio->uio_td, td));
        KASSERT(flags & FOF_OFFSET, ("No FOF_OFFSET"));
        vp = fp->f_vnode;
        if (vp->v_type == VREG)
                bwillwrite();
        ioflag = IO_UNIT;
        if (vp->v_type == VREG && (fp->f_flag & O_APPEND))
                ioflag |= IO_APPEND;
        if (fp->f_flag & FNONBLOCK)
                ioflag |= IO_NDELAY;
        if (fp->f_flag & O_DIRECT)
                ioflag |= IO_DIRECT;
        if ((fp->f_flag & O_FSYNC) ||
            (vp->v_mount && (vp->v_mount->mnt_flag & MNT_SYNCHRONOUS)))
                ioflag |= IO_SYNC;
        mp = NULL;
        if (vp->v_type != VCHR &&
            (error = vn_start_write(vp, &mp, V_WAIT | PCATCH)) != 0)
                goto unlock;

        advice = get_advice(fp, uio);

        if (MNT_SHARED_WRITES(mp) ||
            (mp == NULL && MNT_SHARED_WRITES(vp->v_mount))) {
                lock_flags = LK_SHARED;
        } else {
                lock_flags = LK_EXCLUSIVE;
        }

        vn_lock(vp, lock_flags | LK_RETRY);
        switch (advice) {
        case POSIX_FADV_NORMAL:
        case POSIX_FADV_SEQUENTIAL:
        case POSIX_FADV_NOREUSE:
                ioflag |= sequential_heuristic(uio, fp);
                break;
        case POSIX_FADV_RANDOM:
                /* XXX: Is this correct? */
                break;
        }
        orig_offset = uio->uio_offset;

#ifdef MAC
        error = mac_vnode_check_write(active_cred, fp->f_cred, vp);
        if (error == 0)
#endif
                error = VOP_WRITE(vp, uio, ioflag, fp->f_cred);
        fp->f_nextoff[UIO_WRITE] = uio->uio_offset;
        VOP_UNLOCK(vp);
        if (vp->v_type != VCHR)
                vn_finished_write(mp);
        if (error == 0 && advice == POSIX_FADV_NOREUSE &&
            orig_offset != uio->uio_offset)
                /*
                 * Use POSIX_FADV_DONTNEED to flush pages and buffers
                 * for the backing file after a POSIX_FADV_NOREUSE
                 * write(2).
                 */
                error = VOP_ADVISE(vp, orig_offset, uio->uio_offset - 1,
                    POSIX_FADV_DONTNEED);
unlock:
        return (error);
}

/*
 * The vn_io_fault() is a wrapper around vn_read() and vn_write() to
 * prevent the following deadlock:
 *
 * Assume that the thread A reads from the vnode vp1 into userspace
 * buffer buf1 backed by the pages of vnode vp2.  If a page in buf1 is
 * currently not resident, then system ends up with the call chain
 *   vn_read() -> VOP_READ(vp1) -> uiomove() -> [Page Fault] ->
 *     vm_fault(buf1) -> vnode_pager_getpages(vp2) -> VOP_GETPAGES(vp2)
 * which establishes lock order vp1->vn_lock, then vp2->vn_lock.
 * If, at the same time, thread B reads from vnode vp2 into buffer buf2
 * backed by the pages of vnode vp1, and some page in buf2 is not
 * resident, we get a reversed order vp2->vn_lock, then vp1->vn_lock.
 *
 * To prevent the lock order reversal and deadlock, vn_io_fault() does
 * not allow page faults to happen during VOP_READ() or VOP_WRITE().
 * Instead, it first tries to do the whole range i/o with pagefaults
 * disabled. If all pages in the i/o buffer are resident and mapped,
 * VOP will succeed (ignoring the genuine filesystem errors).
 * Otherwise, we get back EFAULT, and vn_io_fault() falls back to do
 * i/o in chunks, with all pages in the chunk prefaulted and held
 * using vm_fault_quick_hold_pages().
 *
 * Filesystems using this deadlock avoidance scheme should use the
 * array of the held pages from uio, saved in the curthread->td_ma,
 * instead of doing uiomove().  A helper function
 * vn_io_fault_uiomove() converts uiomove request into
 * uiomove_fromphys() over td_ma array.
 *
 * Since vnode locks do not cover the whole i/o anymore, rangelocks
 * make the current i/o request atomic with respect to other i/os and
 * truncations.
 */

/*
 * Decode vn_io_fault_args and perform the corresponding i/o.
 */
static int
vn_io_fault_doio(struct vn_io_fault_args *args, struct uio *uio,
    struct thread *td)
{
        int error, save;

        error = 0;
        save = vm_fault_disable_pagefaults();
        switch (args->kind) {
        case VN_IO_FAULT_FOP:
                error = (args->args.fop_args.doio)(args->args.fop_args.fp,
                    uio, args->cred, args->flags, td);
                break;
        case VN_IO_FAULT_VOP:
                if (uio->uio_rw == UIO_READ) {
                        error = VOP_READ(args->args.vop_args.vp, uio,
                            args->flags, args->cred);
                } else if (uio->uio_rw == UIO_WRITE) {
                        error = VOP_WRITE(args->args.vop_args.vp, uio,
                            args->flags, args->cred);
                }
                break;
        default:
                panic("vn_io_fault_doio: unknown kind of io %d %d",
                    args->kind, uio->uio_rw);
        }
        vm_fault_enable_pagefaults(save);
        return (error);
}

static int
vn_io_fault_touch(char *base, const struct uio *uio)
{
        int r;

        r = fubyte(base);
        if (r == -1 || (uio->uio_rw == UIO_READ && subyte(base, r) == -1))
                return (EFAULT);
        return (0);
}

static int
vn_io_fault_prefault_user(const struct uio *uio)
{
        char *base;
        const struct iovec *iov;
        size_t len;
        ssize_t resid;
        int error, i;

        KASSERT(uio->uio_segflg == UIO_USERSPACE,
            ("vn_io_fault_prefault userspace"));

        error = i = 0;
        iov = uio->uio_iov;
        resid = uio->uio_resid;
        base = iov->iov_base;
        len = iov->iov_len;
        while (resid > 0) {
                error = vn_io_fault_touch(base, uio);
                if (error != 0)
                        break;
                if (len < PAGE_SIZE) {
                        if (len != 0) {
                                error = vn_io_fault_touch(base + len - 1, uio);
                                if (error != 0)
                                        break;
                                resid -= len;
                        }
                        if (++i >= uio->uio_iovcnt)
                                break;
                        iov = uio->uio_iov + i;
                        base = iov->iov_base;
                        len = iov->iov_len;
                } else {
                        len -= PAGE_SIZE;
                        base += PAGE_SIZE;
                        resid -= PAGE_SIZE;
                }
        }
        return (error);
}

/*
 * Common code for vn_io_fault(), agnostic to the kind of i/o request.
 * Uses vn_io_fault_doio() to make the call to an actual i/o function.
 * Used from vn_rdwr() and vn_io_fault(), which encode the i/o request
 * into args and call vn_io_fault1() to handle faults during the user
 * mode buffer accesses.
 */
static int
vn_io_fault1(struct vnode *vp, struct uio *uio, struct vn_io_fault_args *args,
    struct thread *td)
{
        vm_page_t ma[io_hold_cnt + 2];
        struct uio *uio_clone, short_uio;
        struct iovec short_iovec[1];
        vm_page_t *prev_td_ma;
        vm_prot_t prot;
        vm_offset_t addr, end;
        size_t len, resid;
        ssize_t adv;
        int error, cnt, saveheld, prev_td_ma_cnt;

        if (vn_io_fault_prefault) {
                error = vn_io_fault_prefault_user(uio);
                if (error != 0)
                        return (error); /* Or ignore ? */
        }

        prot = uio->uio_rw == UIO_READ ? VM_PROT_WRITE : VM_PROT_READ;

        /*
         * The UFS follows IO_UNIT directive and replays back both
         * uio_offset and uio_resid if an error is encountered during the
         * operation.  But, since the iovec may be already advanced,
         * uio is still in an inconsistent state.
         *
         * Cache a copy of the original uio, which is advanced to the redo
         * point using UIO_NOCOPY below.
         */
        uio_clone = cloneuio(uio);
        resid = uio->uio_resid;

        short_uio.uio_segflg = UIO_USERSPACE;
        short_uio.uio_rw = uio->uio_rw;
        short_uio.uio_td = uio->uio_td;

        error = vn_io_fault_doio(args, uio, td);
        if (error != EFAULT)
                goto out;

        atomic_add_long(&vn_io_faults_cnt, 1);
        uio_clone->uio_segflg = UIO_NOCOPY;
        uiomove(NULL, resid - uio->uio_resid, uio_clone);
        uio_clone->uio_segflg = uio->uio_segflg;

        saveheld = curthread_pflags_set(TDP_UIOHELD);
        prev_td_ma = td->td_ma;
        prev_td_ma_cnt = td->td_ma_cnt;

        while (uio_clone->uio_resid != 0) {
                len = uio_clone->uio_iov->iov_len;
                if (len == 0) {
                        KASSERT(uio_clone->uio_iovcnt >= 1,
                            ("iovcnt underflow"));
                        uio_clone->uio_iov++;
                        uio_clone->uio_iovcnt--;
                        continue;
                }
                if (len > ptoa(io_hold_cnt))
                        len = ptoa(io_hold_cnt);
                addr = (uintptr_t)uio_clone->uio_iov->iov_base;
                end = round_page(addr + len);
                if (end < addr) {
                        error = EFAULT;
                        break;
                }
                cnt = atop(end - trunc_page(addr));
                /*
                 * A perfectly misaligned address and length could cause
                 * both the start and the end of the chunk to use partial
                 * page.  +2 accounts for such a situation.
                 */
                cnt = vm_fault_quick_hold_pages(&td->td_proc->p_vmspace->vm_map,
                    addr, len, prot, ma, io_hold_cnt + 2);
                if (cnt == -1) {
                        error = EFAULT;
                        break;
                }
                short_uio.uio_iov = &short_iovec[0];
                short_iovec[0].iov_base = (void *)addr;
                short_uio.uio_iovcnt = 1;
                short_uio.uio_resid = short_iovec[0].iov_len = len;
                short_uio.uio_offset = uio_clone->uio_offset;
                td->td_ma = ma;
                td->td_ma_cnt = cnt;

                error = vn_io_fault_doio(args, &short_uio, td);
                vm_page_unhold_pages(ma, cnt);
                adv = len - short_uio.uio_resid;

                uio_clone->uio_iov->iov_base =
                    (char *)uio_clone->uio_iov->iov_base + adv;
                uio_clone->uio_iov->iov_len -= adv;
                uio_clone->uio_resid -= adv;
                uio_clone->uio_offset += adv;

                uio->uio_resid -= adv;
                uio->uio_offset += adv;

                if (error != 0 || adv == 0)
                        break;
        }
        td->td_ma = prev_td_ma;
        td->td_ma_cnt = prev_td_ma_cnt;
        curthread_pflags_restore(saveheld);
out:
        free(uio_clone, M_IOV);
        return (error);
}

static int
vn_io_fault(struct file *fp, struct uio *uio, struct ucred *active_cred,
    int flags, struct thread *td)
{
        fo_rdwr_t *doio;
        struct vnode *vp;
        void *rl_cookie;
        struct vn_io_fault_args args;
        int error;

        doio = uio->uio_rw == UIO_READ ? vn_read : vn_write;
        vp = fp->f_vnode;

        /*
         * The ability to read(2) on a directory has historically been
         * allowed for all users, but this can and has been the source of
         * at least one security issue in the past.  As such, it is now hidden
         * away behind a sysctl for those that actually need it to use it, and
         * restricted to root when it's turned on to make it relatively safe to
         * leave on for longer sessions of need.
         */
        if (vp->v_type == VDIR) {
                KASSERT(uio->uio_rw == UIO_READ,
                    ("illegal write attempted on a directory"));
                if (!vfs_allow_read_dir)
                        return (EISDIR);
                if ((error = priv_check(td, PRIV_VFS_READ_DIR)) != 0)
                        return (EISDIR);
        }

        foffset_lock_uio(fp, uio, flags);
        if (do_vn_io_fault(vp, uio)) {
                args.kind = VN_IO_FAULT_FOP;
                args.args.fop_args.fp = fp;
                args.args.fop_args.doio = doio;
                args.cred = active_cred;
                args.flags = flags | FOF_OFFSET;
                if (uio->uio_rw == UIO_READ) {
                        rl_cookie = vn_rangelock_rlock(vp, uio->uio_offset,
                            uio->uio_offset + uio->uio_resid);
                } else if ((fp->f_flag & O_APPEND) != 0 ||
                    (flags & FOF_OFFSET) == 0) {
                        /* For appenders, punt and lock the whole range. */
                        rl_cookie = vn_rangelock_wlock(vp, 0, OFF_MAX);
                } else {
                        rl_cookie = vn_rangelock_wlock(vp, uio->uio_offset,
                            uio->uio_offset + uio->uio_resid);
                }
                error = vn_io_fault1(vp, uio, &args, td);
                vn_rangelock_unlock(vp, rl_cookie);
        } else {
                error = doio(fp, uio, active_cred, flags | FOF_OFFSET, td);
        }
        foffset_unlock_uio(fp, uio, flags);
        return (error);
}

/*
 * Helper function to perform the requested uiomove operation using
 * the held pages for io->uio_iov[0].iov_base buffer instead of
 * copyin/copyout.  Access to the pages with uiomove_fromphys()
 * instead of iov_base prevents page faults that could occur due to
 * pmap_collect() invalidating the mapping created by
 * vm_fault_quick_hold_pages(), or pageout daemon, page laundry or
 * object cleanup revoking the write access from page mappings.
 *
 * Filesystems specified MNTK_NO_IOPF shall use vn_io_fault_uiomove()
 * instead of plain uiomove().
 */
int
vn_io_fault_uiomove(char *data, int xfersize, struct uio *uio)
{
        struct uio transp_uio;
        struct iovec transp_iov[1];
        struct thread *td;
        size_t adv;
        int error, pgadv;

        td = curthread;
        if ((td->td_pflags & TDP_UIOHELD) == 0 ||
            uio->uio_segflg != UIO_USERSPACE)
                return (uiomove(data, xfersize, uio));

        KASSERT(uio->uio_iovcnt == 1, ("uio_iovcnt %d", uio->uio_iovcnt));
        transp_iov[0].iov_base = data;
        transp_uio.uio_iov = &transp_iov[0];
        transp_uio.uio_iovcnt = 1;
        if (xfersize > uio->uio_resid)
                xfersize = uio->uio_resid;
        transp_uio.uio_resid = transp_iov[0].iov_len = xfersize;
        transp_uio.uio_offset = 0;
        transp_uio.uio_segflg = UIO_SYSSPACE;
        /*
         * Since transp_iov points to data, and td_ma page array
         * corresponds to original uio->uio_iov, we need to invert the
         * direction of the i/o operation as passed to
         * uiomove_fromphys().
         */
        switch (uio->uio_rw) {
        case UIO_WRITE:
                transp_uio.uio_rw = UIO_READ;
                break;
        case UIO_READ:
                transp_uio.uio_rw = UIO_WRITE;
                break;
        }
        transp_uio.uio_td = uio->uio_td;
        error = uiomove_fromphys(td->td_ma,
            ((vm_offset_t)uio->uio_iov->iov_base) & PAGE_MASK,
            xfersize, &transp_uio);
        adv = xfersize - transp_uio.uio_resid;
        pgadv =
            (((vm_offset_t)uio->uio_iov->iov_base + adv) >> PAGE_SHIFT) -
            (((vm_offset_t)uio->uio_iov->iov_base) >> PAGE_SHIFT);
        td->td_ma += pgadv;
        KASSERT(td->td_ma_cnt >= pgadv, ("consumed pages %d %d", td->td_ma_cnt,
            pgadv));
        td->td_ma_cnt -= pgadv;
        uio->uio_iov->iov_base = (char *)uio->uio_iov->iov_base + adv;
        uio->uio_iov->iov_len -= adv;
        uio->uio_resid -= adv;
        uio->uio_offset += adv;
        return (error);
}

int
vn_io_fault_pgmove(vm_page_t ma[], vm_offset_t offset, int xfersize,
    struct uio *uio)
{
        struct thread *td;
        vm_offset_t iov_base;
        int cnt, pgadv;

        td = curthread;
        if ((td->td_pflags & TDP_UIOHELD) == 0 ||
            uio->uio_segflg != UIO_USERSPACE)
                return (uiomove_fromphys(ma, offset, xfersize, uio));

        KASSERT(uio->uio_iovcnt == 1, ("uio_iovcnt %d", uio->uio_iovcnt));
        cnt = xfersize > uio->uio_resid ? uio->uio_resid : xfersize;
        iov_base = (vm_offset_t)uio->uio_iov->iov_base;
        switch (uio->uio_rw) {
        case UIO_WRITE:
                pmap_copy_pages(td->td_ma, iov_base & PAGE_MASK, ma,
                    offset, cnt);
                break;
        case UIO_READ:
                pmap_copy_pages(ma, offset, td->td_ma, iov_base & PAGE_MASK,
                    cnt);
                break;
        }
        pgadv = ((iov_base + cnt) >> PAGE_SHIFT) - (iov_base >> PAGE_SHIFT);
        td->td_ma += pgadv;
        KASSERT(td->td_ma_cnt >= pgadv, ("consumed pages %d %d", td->td_ma_cnt,
            pgadv));
        td->td_ma_cnt -= pgadv;
        uio->uio_iov->iov_base = (char *)(iov_base + cnt);
        uio->uio_iov->iov_len -= cnt;
        uio->uio_resid -= cnt;
        uio->uio_offset += cnt;
        return (0);
}

/*
 * File table truncate routine.
 */
static int
vn_truncate(struct file *fp, off_t length, struct ucred *active_cred,
    struct thread *td)
{
        struct mount *mp;
        struct vnode *vp;
        void *rl_cookie;
        int error;

        vp = fp->f_vnode;

        /*
         * Lock the whole range for truncation.  Otherwise split i/o
         * might happen partly before and partly after the truncation.
         */
        rl_cookie = vn_rangelock_wlock(vp, 0, OFF_MAX);
        error = vn_start_write(vp, &mp, V_WAIT | PCATCH);
        if (error)
                goto out1;
        vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
        AUDIT_ARG_VNODE1(vp);
        if (vp->v_type == VDIR) {
                error = EISDIR;
                goto out;
        }
#ifdef MAC
        error = mac_vnode_check_write(active_cred, fp->f_cred, vp);
        if (error)
                goto out;
#endif
        error = vn_truncate_locked(vp, length, (fp->f_flag & O_FSYNC) != 0,
            fp->f_cred);
out:
        VOP_UNLOCK(vp);
        vn_finished_write(mp);
out1:
        vn_rangelock_unlock(vp, rl_cookie);
        return (error);
}

/*
 * Truncate a file that is already locked.
 */
int
vn_truncate_locked(struct vnode *vp, off_t length, bool sync,
    struct ucred *cred)
{
        struct vattr vattr;
        int error;

        error = VOP_ADD_WRITECOUNT(vp, 1);
        if (error == 0) {
                VATTR_NULL(&vattr);
                vattr.va_size = length;
                if (sync)
                        vattr.va_vaflags |= VA_SYNC;
                error = VOP_SETATTR(vp, &vattr, cred);
                VOP_ADD_WRITECOUNT_CHECKED(vp, -1);
        }
        return (error);
}

/*
 * File table vnode stat routine.
 */
static int
vn_statfile(struct file *fp, struct stat *sb, struct ucred *active_cred,
    struct thread *td)
{
        struct vnode *vp = fp->f_vnode;
        int error;

        vn_lock(vp, LK_SHARED | LK_RETRY);
        error = VOP_STAT(vp, sb, active_cred, fp->f_cred, td);
        VOP_UNLOCK(vp);

        return (error);
}

/*
 * File table vnode ioctl routine.
 */
static int
vn_ioctl(struct file *fp, u_long com, void *data, struct ucred *active_cred,
    struct thread *td)
{
        struct vattr vattr;
        struct vnode *vp;
        struct fiobmap2_arg *bmarg;
        int error;

        vp = fp->f_vnode;
        switch (vp->v_type) {
        case VDIR:
        case VREG:
                switch (com) {
                case FIONREAD:
                        vn_lock(vp, LK_SHARED | LK_RETRY);
                        error = VOP_GETATTR(vp, &vattr, active_cred);
                        VOP_UNLOCK(vp);
                        if (error == 0)
                                *(int *)data = vattr.va_size - fp->f_offset;
                        return (error);
                case FIOBMAP2:
                        bmarg = (struct fiobmap2_arg *)data;
                        vn_lock(vp, LK_SHARED | LK_RETRY);
#ifdef MAC
                        error = mac_vnode_check_read(active_cred, fp->f_cred,
                            vp);
                        if (error == 0)
#endif
                                error = VOP_BMAP(vp, bmarg->bn, NULL,
                                    &bmarg->bn, &bmarg->runp, &bmarg->runb);
                        VOP_UNLOCK(vp);
                        return (error);
                case FIONBIO:
                case FIOASYNC:
                        return (0);
                default:
                        return (VOP_IOCTL(vp, com, data, fp->f_flag,
                            active_cred, td));
                }
                break;
        case VCHR:
                return (VOP_IOCTL(vp, com, data, fp->f_flag,
                    active_cred, td));
        default:
                return (ENOTTY);
        }
}

/*
 * File table vnode poll routine.
 */
static int
vn_poll(struct file *fp, int events, struct ucred *active_cred,
    struct thread *td)
{
        struct vnode *vp;
        int error;

        vp = fp->f_vnode;
#if defined(MAC) || defined(AUDIT)
        if (AUDITING_TD(td) || mac_vnode_check_poll_enabled()) {
                vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
                AUDIT_ARG_VNODE1(vp);
                error = mac_vnode_check_poll(active_cred, fp->f_cred, vp);
                VOP_UNLOCK(vp);
                if (error != 0)
                        return (error);
        }
#endif
        error = VOP_POLL(vp, events, fp->f_cred, td);
        return (error);
}

/*
 * Acquire the requested lock and then check for validity.  LK_RETRY
 * permits vn_lock to return doomed vnodes.
 */
static int __noinline
_vn_lock_fallback(struct vnode *vp, int flags, const char *file, int line,
    int error)
{

        KASSERT((flags & LK_RETRY) == 0 || error == 0,
            ("vn_lock: error %d incompatible with flags %#x", error, flags));

        if (error == 0)
                VNASSERT(VN_IS_DOOMED(vp), vp, ("vnode not doomed"));

        if ((flags & LK_RETRY) == 0) {
                if (error == 0) {
                        VOP_UNLOCK(vp);
                        error = ENOENT;
                }
                return (error);
        }

        /*
         * LK_RETRY case.
         *
         * Nothing to do if we got the lock.
         */
        if (error == 0)
                return (0);

        /*
         * Interlock was dropped by the call in _vn_lock.
         */
        flags &= ~LK_INTERLOCK;
        do {
                error = VOP_LOCK1(vp, flags, file, line);
        } while (error != 0);
        return (0);
}

int
_vn_lock(struct vnode *vp, int flags, const char *file, int line)
{
        int error;

        VNASSERT((flags & LK_TYPE_MASK) != 0, vp,
            ("vn_lock: no locktype (%d passed)", flags));
        VNPASS(vp->v_holdcnt > 0, vp);
        error = VOP_LOCK1(vp, flags, file, line);
        if (__predict_false(error != 0 || VN_IS_DOOMED(vp)))
                return (_vn_lock_fallback(vp, flags, file, line, error));
        return (0);
}

/*
 * File table vnode close routine.
 */
static int
vn_closefile(struct file *fp, struct thread *td)
{
        struct vnode *vp;
        struct flock lf;
        int error;
        bool ref;

        vp = fp->f_vnode;
        fp->f_ops = &badfileops;
        ref= (fp->f_flag & FHASLOCK) != 0 && fp->f_type == DTYPE_VNODE;

        error = vn_close1(vp, fp->f_flag, fp->f_cred, td, ref);

        if (__predict_false(ref)) {
                lf.l_whence = SEEK_SET;
                lf.l_start = 0;
                lf.l_len = 0;
                lf.l_type = F_UNLCK;
                (void) VOP_ADVLOCK(vp, fp, F_UNLCK, &lf, F_FLOCK);
                vrele(vp);
        }
        return (error);
}

/*
 * Preparing to start a filesystem write operation. If the operation is
 * permitted, then we bump the count of operations in progress and
 * proceed. If a suspend request is in progress, we wait until the
 * suspension is over, and then proceed.
 */
static int
vn_start_write_refed(struct mount *mp, int flags, bool mplocked)
{
        int error, mflags;

        if (__predict_true(!mplocked) && (flags & V_XSLEEP) == 0 &&
            vfs_op_thread_enter(mp)) {
                MPASS((mp->mnt_kern_flag & MNTK_SUSPEND) == 0);
                vfs_mp_count_add_pcpu(mp, writeopcount, 1);
                vfs_op_thread_exit(mp);
                return (0);
        }

        if (mplocked)
                mtx_assert(MNT_MTX(mp), MA_OWNED);
        else
                MNT_ILOCK(mp);

        error = 0;

        /*
         * Check on status of suspension.
         */
        if ((curthread->td_pflags & TDP_IGNSUSP) == 0 ||
            mp->mnt_susp_owner != curthread) {
                mflags = ((mp->mnt_vfc->vfc_flags & VFCF_SBDRY) != 0 ?
                    (flags & PCATCH) : 0) | (PUSER - 1);
                while ((mp->mnt_kern_flag & MNTK_SUSPEND) != 0) {
                        if (flags & V_NOWAIT) {
                                error = EWOULDBLOCK;
                                goto unlock;
                        }
                        error = msleep(&mp->mnt_flag, MNT_MTX(mp), mflags,
                            "suspfs", 0);
                        if (error)
                                goto unlock;
                }
        }
        if (flags & V_XSLEEP)
                goto unlock;
        mp->mnt_writeopcount++;
unlock:
        if (error != 0 || (flags & V_XSLEEP) != 0)
                MNT_REL(mp);
        MNT_IUNLOCK(mp);
        return (error);
}

int
vn_start_write(struct vnode *vp, struct mount **mpp, int flags)
{
        struct mount *mp;
        int error;

        KASSERT((flags & V_MNTREF) == 0 || (*mpp != NULL && vp == NULL),
            ("V_MNTREF requires mp"));

        error = 0;
        /*
         * If a vnode is provided, get and return the mount point that
         * to which it will write.
         */
        if (vp != NULL) {
                if ((error = VOP_GETWRITEMOUNT(vp, mpp)) != 0) {
                        *mpp = NULL;
                        if (error != EOPNOTSUPP)
                                return (error);
                        return (0);
                }
        }
        if ((mp = *mpp) == NULL)
                return (0);

        /*
         * VOP_GETWRITEMOUNT() returns with the mp refcount held through
         * a vfs_ref().
         * As long as a vnode is not provided we need to acquire a
         * refcount for the provided mountpoint too, in order to
         * emulate a vfs_ref().
         */
        if (vp == NULL && (flags & V_MNTREF) == 0)
                vfs_ref(mp);

        return (vn_start_write_refed(mp, flags, false));
}

/*
 * Secondary suspension. Used by operations such as vop_inactive
 * routines that are needed by the higher level functions. These
 * are allowed to proceed until all the higher level functions have
 * completed (indicated by mnt_writeopcount dropping to zero). At that
 * time, these operations are halted until the suspension is over.
 */
int
vn_start_secondary_write(struct vnode *vp, struct mount **mpp, int flags)
{
        struct mount *mp;
        int error;

        KASSERT((flags & V_MNTREF) == 0 || (*mpp != NULL && vp == NULL),
            ("V_MNTREF requires mp"));

 retry:
        if (vp != NULL) {
                if ((error = VOP_GETWRITEMOUNT(vp, mpp)) != 0) {
                        *mpp = NULL;
                        if (error != EOPNOTSUPP)
                                return (error);
                        return (0);
                }
        }
        /*
         * If we are not suspended or have not yet reached suspended
         * mode, then let the operation proceed.
         */
        if ((mp = *mpp) == NULL)
                return (0);

        /*
         * VOP_GETWRITEMOUNT() returns with the mp refcount held through
         * a vfs_ref().
         * As long as a vnode is not provided we need to acquire a
         * refcount for the provided mountpoint too, in order to
         * emulate a vfs_ref().
         */
        MNT_ILOCK(mp);
        if (vp == NULL && (flags & V_MNTREF) == 0)
                MNT_REF(mp);
        if ((mp->mnt_kern_flag & (MNTK_SUSPENDED | MNTK_SUSPEND2)) == 0) {
                mp->mnt_secondary_writes++;
                mp->mnt_secondary_accwrites++;
                MNT_IUNLOCK(mp);
                return (0);
        }
        if (flags & V_NOWAIT) {
                MNT_REL(mp);
                MNT_IUNLOCK(mp);
                return (EWOULDBLOCK);
        }
        /*
         * Wait for the suspension to finish.
         */
        error = msleep(&mp->mnt_flag, MNT_MTX(mp), (PUSER - 1) | PDROP |
            ((mp->mnt_vfc->vfc_flags & VFCF_SBDRY) != 0 ? (flags & PCATCH) : 0),
            "suspfs", 0);
        vfs_rel(mp);
        if (error == 0)
                goto retry;
        return (error);
}

/*
 * Filesystem write operation has completed. If we are suspending and this
 * operation is the last one, notify the suspender that the suspension is
 * now in effect.
 */
void
vn_finished_write(struct mount *mp)
{
        int c;

        if (mp == NULL)
                return;

        if (vfs_op_thread_enter(mp)) {
                vfs_mp_count_sub_pcpu(mp, writeopcount, 1);
                vfs_mp_count_sub_pcpu(mp, ref, 1);
                vfs_op_thread_exit(mp);
                return;
        }

        MNT_ILOCK(mp);
        vfs_assert_mount_counters(mp);
        MNT_REL(mp);
        c = --mp->mnt_writeopcount;
        if (mp->mnt_vfs_ops == 0) {
                MPASS((mp->mnt_kern_flag & MNTK_SUSPEND) == 0);
                MNT_IUNLOCK(mp);
                return;
        }
        if (c < 0)
                vfs_dump_mount_counters(mp);
        if ((mp->mnt_kern_flag & MNTK_SUSPEND) != 0 && c == 0)
                wakeup(&mp->mnt_writeopcount);
        MNT_IUNLOCK(mp);
}

/*
 * Filesystem secondary write operation has completed. If we are
 * suspending and this operation is the last one, notify the suspender
 * that the suspension is now in effect.
 */
void
vn_finished_secondary_write(struct mount *mp)
{
        if (mp == NULL)
                return;
        MNT_ILOCK(mp);
        MNT_REL(mp);
        mp->mnt_secondary_writes--;
        if (mp->mnt_secondary_writes < 0)
                panic("vn_finished_secondary_write: neg cnt");
        if ((mp->mnt_kern_flag & MNTK_SUSPEND) != 0 &&
            mp->mnt_secondary_writes <= 0)
                wakeup(&mp->mnt_secondary_writes);
        MNT_IUNLOCK(mp);
}

/*
 * Request a filesystem to suspend write operations.
 */
int
vfs_write_suspend(struct mount *mp, int flags)
{
        int error;

        vfs_op_enter(mp);

        MNT_ILOCK(mp);
        vfs_assert_mount_counters(mp);
        if (mp->mnt_susp_owner == curthread) {
                vfs_op_exit_locked(mp);
                MNT_IUNLOCK(mp);
                return (EALREADY);
        }
        while (mp->mnt_kern_flag & MNTK_SUSPEND)
                msleep(&mp->mnt_flag, MNT_MTX(mp), PUSER - 1, "wsuspfs", 0);

        /*
         * Unmount holds a write reference on the mount point.  If we
         * own busy reference and drain for writers, we deadlock with
         * the reference draining in the unmount path.  Callers of
         * vfs_write_suspend() must specify VS_SKIP_UNMOUNT if
         * vfs_busy() reference is owned and caller is not in the
         * unmount context.
         */
        if ((flags & VS_SKIP_UNMOUNT) != 0 &&
            (mp->mnt_kern_flag & MNTK_UNMOUNT) != 0) {
                vfs_op_exit_locked(mp);
                MNT_IUNLOCK(mp);
                return (EBUSY);
        }

        mp->mnt_kern_flag |= MNTK_SUSPEND;
        mp->mnt_susp_owner = curthread;
        if (mp->mnt_writeopcount > 0)
                (void) msleep(&mp->mnt_writeopcount, 
                    MNT_MTX(mp), (PUSER - 1)|PDROP, "suspwt", 0);
        else
                MNT_IUNLOCK(mp);
        if ((error = VFS_SYNC(mp, MNT_SUSPEND)) != 0) {
                vfs_write_resume(mp, 0);
                /* vfs_write_resume does vfs_op_exit() for us */
        }
        return (error);
}

/*
 * Request a filesystem to resume write operations.
 */
void
vfs_write_resume(struct mount *mp, int flags)
{

        MNT_ILOCK(mp);
        if ((mp->mnt_kern_flag & MNTK_SUSPEND) != 0) {
                KASSERT(mp->mnt_susp_owner == curthread, ("mnt_susp_owner"));
                mp->mnt_kern_flag &= ~(MNTK_SUSPEND | MNTK_SUSPEND2 |
                                       MNTK_SUSPENDED);
                mp->mnt_susp_owner = NULL;
                wakeup(&mp->mnt_writeopcount);
                wakeup(&mp->mnt_flag);
                curthread->td_pflags &= ~TDP_IGNSUSP;
                if ((flags & VR_START_WRITE) != 0) {
                        MNT_REF(mp);
                        mp->mnt_writeopcount++;
                }
                MNT_IUNLOCK(mp);
                if ((flags & VR_NO_SUSPCLR) == 0)
                        VFS_SUSP_CLEAN(mp);
                vfs_op_exit(mp);
        } else if ((flags & VR_START_WRITE) != 0) {
                MNT_REF(mp);
                vn_start_write_refed(mp, 0, true);
        } else {
                MNT_IUNLOCK(mp);
        }
}

/*
 * Helper loop around vfs_write_suspend() for filesystem unmount VFS
 * methods.
 */
int
vfs_write_suspend_umnt(struct mount *mp)
{
        int error;

        KASSERT((curthread->td_pflags & TDP_IGNSUSP) == 0,
            ("vfs_write_suspend_umnt: recursed"));

        /* dounmount() already called vn_start_write(). */
        for (;;) {
                vn_finished_write(mp);
                error = vfs_write_suspend(mp, 0);
                if (error != 0) {
                        vn_start_write(NULL, &mp, V_WAIT);
                        return (error);
                }
                MNT_ILOCK(mp);
                if ((mp->mnt_kern_flag & MNTK_SUSPENDED) != 0)
                        break;
                MNT_IUNLOCK(mp);
                vn_start_write(NULL, &mp, V_WAIT);
        }
        mp->mnt_kern_flag &= ~(MNTK_SUSPENDED | MNTK_SUSPEND2);
        wakeup(&mp->mnt_flag);
        MNT_IUNLOCK(mp);
        curthread->td_pflags |= TDP_IGNSUSP;
        return (0);
}

/*
 * Implement kqueues for files by translating it to vnode operation.
 */
static int
vn_kqfilter(struct file *fp, struct knote *kn)
{

        return (VOP_KQFILTER(fp->f_vnode, kn));
}

/*
 * Simplified in-kernel wrapper calls for extended attribute access.
 * Both calls pass in a NULL credential, authorizing as "kernel" access.
 * Set IO_NODELOCKED in ioflg if the vnode is already locked.
 */
int
vn_extattr_get(struct vnode *vp, int ioflg, int attrnamespace,
    const char *attrname, int *buflen, char *buf, struct thread *td)
{
        struct uio      auio;
        struct iovec    iov;
        int     error;

        iov.iov_len = *buflen;
        iov.iov_base = buf;

        auio.uio_iov = &iov;
        auio.uio_iovcnt = 1;
        auio.uio_rw = UIO_READ;
        auio.uio_segflg = UIO_SYSSPACE;
        auio.uio_td = td;
        auio.uio_offset = 0;
        auio.uio_resid = *buflen;

        if ((ioflg & IO_NODELOCKED) == 0)
                vn_lock(vp, LK_SHARED | LK_RETRY);

        ASSERT_VOP_LOCKED(vp, "IO_NODELOCKED with no vp lock held");

        /* authorize attribute retrieval as kernel */
        error = VOP_GETEXTATTR(vp, attrnamespace, attrname, &auio, NULL, NULL,
            td);

        if ((ioflg & IO_NODELOCKED) == 0)
                VOP_UNLOCK(vp);

        if (error == 0) {
                *buflen = *buflen - auio.uio_resid;
        }

        return (error);
}

/*
 * XXX failure mode if partially written?
 */
int
vn_extattr_set(struct vnode *vp, int ioflg, int attrnamespace,
    const char *attrname, int buflen, char *buf, struct thread *td)
{
        struct uio      auio;
        struct iovec    iov;
        struct mount    *mp;
        int     error;

        iov.iov_len = buflen;
        iov.iov_base = buf;

        auio.uio_iov = &iov;
        auio.uio_iovcnt = 1;
        auio.uio_rw = UIO_WRITE;
        auio.uio_segflg = UIO_SYSSPACE;
        auio.uio_td = td;
        auio.uio_offset = 0;
        auio.uio_resid = buflen;

        if ((ioflg & IO_NODELOCKED) == 0) {
                if ((error = vn_start_write(vp, &mp, V_WAIT)) != 0)
                        return (error);
                vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
        }

        ASSERT_VOP_LOCKED(vp, "IO_NODELOCKED with no vp lock held");

        /* authorize attribute setting as kernel */
        error = VOP_SETEXTATTR(vp, attrnamespace, attrname, &auio, NULL, td);

        if ((ioflg & IO_NODELOCKED) == 0) {
                vn_finished_write(mp);
                VOP_UNLOCK(vp);
        }

        return (error);
}

int
vn_extattr_rm(struct vnode *vp, int ioflg, int attrnamespace,
    const char *attrname, struct thread *td)
{
        struct mount    *mp;
        int     error;

        if ((ioflg & IO_NODELOCKED) == 0) {
                if ((error = vn_start_write(vp, &mp, V_WAIT)) != 0)
                        return (error);
                vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
        }

        ASSERT_VOP_LOCKED(vp, "IO_NODELOCKED with no vp lock held");

        /* authorize attribute removal as kernel */
        error = VOP_DELETEEXTATTR(vp, attrnamespace, attrname, NULL, td);
        if (error == EOPNOTSUPP)
                error = VOP_SETEXTATTR(vp, attrnamespace, attrname, NULL,
                    NULL, td);

        if ((ioflg & IO_NODELOCKED) == 0) {
                vn_finished_write(mp);
                VOP_UNLOCK(vp);
        }

        return (error);
}

static int
vn_get_ino_alloc_vget(struct mount *mp, void *arg, int lkflags,
    struct vnode **rvp)
{

        return (VFS_VGET(mp, *(ino_t *)arg, lkflags, rvp));
}

int
vn_vget_ino(struct vnode *vp, ino_t ino, int lkflags, struct vnode **rvp)
{

        return (vn_vget_ino_gen(vp, vn_get_ino_alloc_vget, &ino,
            lkflags, rvp));
}

int
vn_vget_ino_gen(struct vnode *vp, vn_get_ino_t alloc, void *alloc_arg,
    int lkflags, struct vnode **rvp)
{
        struct mount *mp;
        int ltype, error;

        ASSERT_VOP_LOCKED(vp, "vn_vget_ino_get");
        mp = vp->v_mount;
        ltype = VOP_ISLOCKED(vp);
        KASSERT(ltype == LK_EXCLUSIVE || ltype == LK_SHARED,
            ("vn_vget_ino: vp not locked"));
        error = vfs_busy(mp, MBF_NOWAIT);
        if (error != 0) {
                vfs_ref(mp);
                VOP_UNLOCK(vp);
                error = vfs_busy(mp, 0);
                vn_lock(vp, ltype | LK_RETRY);
                vfs_rel(mp);
                if (error != 0)
                        return (ENOENT);
                if (VN_IS_DOOMED(vp)) {
                        vfs_unbusy(mp);
                        return (ENOENT);
                }
        }
        VOP_UNLOCK(vp);
        error = alloc(mp, alloc_arg, lkflags, rvp);
        vfs_unbusy(mp);
        if (error != 0 || *rvp != vp)
                vn_lock(vp, ltype | LK_RETRY);
        if (VN_IS_DOOMED(vp)) {
                if (error == 0) {
                        if (*rvp == vp)
                                vunref(vp);
                        else
                                vput(*rvp);
                }
                error = ENOENT;
        }
        return (error);
}

int
vn_rlimit_fsize(const struct vnode *vp, const struct uio *uio,
    struct thread *td)
{

        if (vp->v_type != VREG || td == NULL)
                return (0);
        if ((uoff_t)uio->uio_offset + uio->uio_resid >
            lim_cur(td, RLIMIT_FSIZE)) {
                PROC_LOCK(td->td_proc);
                kern_psignal(td->td_proc, SIGXFSZ);
                PROC_UNLOCK(td->td_proc);
                return (EFBIG);
        }
        return (0);
}

int
vn_chmod(struct file *fp, mode_t mode, struct ucred *active_cred,
    struct thread *td)
{
        struct vnode *vp;

        vp = fp->f_vnode;
#ifdef AUDIT
        vn_lock(vp, LK_SHARED | LK_RETRY);
        AUDIT_ARG_VNODE1(vp);
        VOP_UNLOCK(vp);
#endif
        return (setfmode(td, active_cred, vp, mode));
}

int
vn_chown(struct file *fp, uid_t uid, gid_t gid, struct ucred *active_cred,
    struct thread *td)
{
        struct vnode *vp;

        vp = fp->f_vnode;
#ifdef AUDIT
        vn_lock(vp, LK_SHARED | LK_RETRY);
        AUDIT_ARG_VNODE1(vp);
        VOP_UNLOCK(vp);
#endif
        return (setfown(td, active_cred, vp, uid, gid));
}

void
vn_pages_remove(struct vnode *vp, vm_pindex_t start, vm_pindex_t end)
{
        vm_object_t object;

        if ((object = vp->v_object) == NULL)
                return;
        VM_OBJECT_WLOCK(object);
        vm_object_page_remove(object, start, end, 0);
        VM_OBJECT_WUNLOCK(object);
}

int
vn_bmap_seekhole(struct vnode *vp, u_long cmd, off_t *off, struct ucred *cred)
{
        struct vattr va;
        daddr_t bn, bnp;
        uint64_t bsize;
        off_t noff;
        int error;

        KASSERT(cmd == FIOSEEKHOLE || cmd == FIOSEEKDATA,
            ("Wrong command %lu", cmd));

        if (vn_lock(vp, LK_SHARED) != 0)
                return (EBADF);
        if (vp->v_type != VREG) {
                error = ENOTTY;
                goto unlock;
        }
        error = VOP_GETATTR(vp, &va, cred);
        if (error != 0)
                goto unlock;
        noff = *off;
        if (noff >= va.va_size) {
                error = ENXIO;
                goto unlock;
        }
        bsize = vp->v_mount->mnt_stat.f_iosize;
        for (bn = noff / bsize; noff < va.va_size; bn++, noff += bsize -
            noff % bsize) {
                error = VOP_BMAP(vp, bn, NULL, &bnp, NULL, NULL);
                if (error == EOPNOTSUPP) {
                        error = ENOTTY;
                        goto unlock;
                }
                if ((bnp == -1 && cmd == FIOSEEKHOLE) ||
                    (bnp != -1 && cmd == FIOSEEKDATA)) {
                        noff = bn * bsize;
                        if (noff < *off)
                                noff = *off;
                        goto unlock;
                }
        }
        if (noff > va.va_size)
                noff = va.va_size;
        /* noff == va.va_size. There is an implicit hole at the end of file. */
        if (cmd == FIOSEEKDATA)
                error = ENXIO;
unlock:
        VOP_UNLOCK(vp);
        if (error == 0)
                *off = noff;
        return (error);
}

int
vn_seek(struct file *fp, off_t offset, int whence, struct thread *td)
{
        struct ucred *cred;
        struct vnode *vp;
        struct vattr vattr;
        off_t foffset, size;
        int error, noneg;

        cred = td->td_ucred;
        vp = fp->f_vnode;
        foffset = foffset_lock(fp, 0);
        noneg = (vp->v_type != VCHR);
        error = 0;
        switch (whence) {
        case L_INCR:
                if (noneg &&
                    (foffset < 0 ||
                    (offset > 0 && foffset > OFF_MAX - offset))) {
                        error = EOVERFLOW;
                        break;
                }
                offset += foffset;
                break;
        case L_XTND:
                vn_lock(vp, LK_SHARED | LK_RETRY);
                error = VOP_GETATTR(vp, &vattr, cred);
                VOP_UNLOCK(vp);
                if (error)
                        break;

                /*
                 * If the file references a disk device, then fetch
                 * the media size and use that to determine the ending
                 * offset.
                 */
                if (vattr.va_size == 0 && vp->v_type == VCHR &&
                    fo_ioctl(fp, DIOCGMEDIASIZE, &size, cred, td) == 0)
                        vattr.va_size = size;
                if (noneg &&
                    (vattr.va_size > OFF_MAX ||
                    (offset > 0 && vattr.va_size > OFF_MAX - offset))) {
                        error = EOVERFLOW;
                        break;
                }
                offset += vattr.va_size;
                break;
        case L_SET:
                break;
        case SEEK_DATA:
                error = fo_ioctl(fp, FIOSEEKDATA, &offset, cred, td);
                if (error == ENOTTY)
                        error = EINVAL;
                break;
        case SEEK_HOLE:
                error = fo_ioctl(fp, FIOSEEKHOLE, &offset, cred, td);
                if (error == ENOTTY)
                        error = EINVAL;
                break;
        default:
                error = EINVAL;
        }
        if (error == 0 && noneg && offset < 0)
                error = EINVAL;
        if (error != 0)
                goto drop;
        VFS_KNOTE_UNLOCKED(vp, 0);
        td->td_uretoff.tdu_off = offset;
drop:
        foffset_unlock(fp, offset, error != 0 ? FOF_NOUPDATE : 0);
        return (error);
}

int
vn_utimes_perm(struct vnode *vp, struct vattr *vap, struct ucred *cred,
    struct thread *td)
{
        int error;

        /*
         * Grant permission if the caller is the owner of the file, or
         * the super-user, or has ACL_WRITE_ATTRIBUTES permission on
         * on the file.  If the time pointer is null, then write
         * permission on the file is also sufficient.
         *
         * From NFSv4.1, draft 21, 6.2.1.3.1, Discussion of Mask Attributes:
         * A user having ACL_WRITE_DATA or ACL_WRITE_ATTRIBUTES
         * will be allowed to set the times [..] to the current
         * server time.
         */
        error = VOP_ACCESSX(vp, VWRITE_ATTRIBUTES, cred, td);
        if (error != 0 && (vap->va_vaflags & VA_UTIMES_NULL) != 0)
                error = VOP_ACCESS(vp, VWRITE, cred, td);
        return (error);
}

int
vn_fill_kinfo(struct file *fp, struct kinfo_file *kif, struct filedesc *fdp)
{
        struct vnode *vp;
        int error;

        if (fp->f_type == DTYPE_FIFO)
                kif->kf_type = KF_TYPE_FIFO;
        else
                kif->kf_type = KF_TYPE_VNODE;
        vp = fp->f_vnode;
        vref(vp);
        FILEDESC_SUNLOCK(fdp);
        error = vn_fill_kinfo_vnode(vp, kif);
        vrele(vp);
        FILEDESC_SLOCK(fdp);
        return (error);
}

static inline void
vn_fill_junk(struct kinfo_file *kif)
{
        size_t len, olen;

        /*
         * Simulate vn_fullpath returning changing values for a given
         * vp during e.g. coredump.
         */
        len = (arc4random() % (sizeof(kif->kf_path) - 2)) + 1;
        olen = strlen(kif->kf_path);
        if (len < olen)
                strcpy(&kif->kf_path[len - 1], "$");
        else
                for (; olen < len; olen++)
                        strcpy(&kif->kf_path[olen], "A");
}

int
vn_fill_kinfo_vnode(struct vnode *vp, struct kinfo_file *kif)
{
        struct vattr va;
        char *fullpath, *freepath;
        int error;

        kif->kf_un.kf_file.kf_file_type = vntype_to_kinfo(vp->v_type);
        freepath = NULL;
        fullpath = "-";
        error = vn_fullpath(vp, &fullpath, &freepath);
        if (error == 0) {
                strlcpy(kif->kf_path, fullpath, sizeof(kif->kf_path));
        }
        if (freepath != NULL)
                free(freepath, M_TEMP);

        KFAIL_POINT_CODE(DEBUG_FP, fill_kinfo_vnode__random_path,
                vn_fill_junk(kif);
        );

        /*
         * Retrieve vnode attributes.
         */
        va.va_fsid = VNOVAL;
        va.va_rdev = NODEV;
        vn_lock(vp, LK_SHARED | LK_RETRY);
        error = VOP_GETATTR(vp, &va, curthread->td_ucred);
        VOP_UNLOCK(vp);
        if (error != 0)
                return (error);
        if (va.va_fsid != VNOVAL)
                kif->kf_un.kf_file.kf_file_fsid = va.va_fsid;
        else
                kif->kf_un.kf_file.kf_file_fsid =
                    vp->v_mount->mnt_stat.f_fsid.val[0];
        kif->kf_un.kf_file.kf_file_fsid_freebsd11 =
            kif->kf_un.kf_file.kf_file_fsid; /* truncate */
        kif->kf_un.kf_file.kf_file_fileid = va.va_fileid;
        kif->kf_un.kf_file.kf_file_mode = MAKEIMODE(va.va_type, va.va_mode);
        kif->kf_un.kf_file.kf_file_size = va.va_size;
        kif->kf_un.kf_file.kf_file_rdev = va.va_rdev;
        kif->kf_un.kf_file.kf_file_rdev_freebsd11 =
            kif->kf_un.kf_file.kf_file_rdev; /* truncate */
        return (0);
}

int
vn_mmap(struct file *fp, vm_map_t map, vm_offset_t *addr, vm_size_t size,
    vm_prot_t prot, vm_prot_t cap_maxprot, int flags, vm_ooffset_t foff,
    struct thread *td)
{
#ifdef HWPMC_HOOKS
        struct pmckern_map_in pkm;
#endif
        struct mount *mp;
        struct vnode *vp;
        vm_object_t object;
        vm_prot_t maxprot;
        boolean_t writecounted;
        int error;

#if defined(COMPAT_FREEBSD7) || defined(COMPAT_FREEBSD6) || \
    defined(COMPAT_FREEBSD5) || defined(COMPAT_FREEBSD4)
        /*
         * POSIX shared-memory objects are defined to have
         * kernel persistence, and are not defined to support
         * read(2)/write(2) -- or even open(2).  Thus, we can
         * use MAP_ASYNC to trade on-disk coherence for speed.
         * The shm_open(3) library routine turns on the FPOSIXSHM
         * flag to request this behavior.
         */
        if ((fp->f_flag & FPOSIXSHM) != 0)
                flags |= MAP_NOSYNC;
#endif
        vp = fp->f_vnode;

        /*
         * Ensure that file and memory protections are
         * compatible.  Note that we only worry about
         * writability if mapping is shared; in this case,
         * current and max prot are dictated by the open file.
         * XXX use the vnode instead?  Problem is: what
         * credentials do we use for determination? What if
         * proc does a setuid?
         */
        mp = vp->v_mount;
        if (mp != NULL && (mp->mnt_flag & MNT_NOEXEC) != 0) {
                maxprot = VM_PROT_NONE;
                if ((prot & VM_PROT_EXECUTE) != 0)
                        return (EACCES);
        } else
                maxprot = VM_PROT_EXECUTE;
        if ((fp->f_flag & FREAD) != 0)
                maxprot |= VM_PROT_READ;
        else if ((prot & VM_PROT_READ) != 0)
                return (EACCES);

        /*
         * If we are sharing potential changes via MAP_SHARED and we
         * are trying to get write permission although we opened it
         * without asking for it, bail out.
         */
        if ((flags & MAP_SHARED) != 0) {
                if ((fp->f_flag & FWRITE) != 0)
                        maxprot |= VM_PROT_WRITE;
                else if ((prot & VM_PROT_WRITE) != 0)
                        return (EACCES);
        } else {
                maxprot |= VM_PROT_WRITE;
                cap_maxprot |= VM_PROT_WRITE;
        }
        maxprot &= cap_maxprot;

        /*
         * For regular files and shared memory, POSIX requires that
         * the value of foff be a legitimate offset within the data
         * object.  In particular, negative offsets are invalid.
         * Blocking negative offsets and overflows here avoids
         * possible wraparound or user-level access into reserved
         * ranges of the data object later.  In contrast, POSIX does
         * not dictate how offsets are used by device drivers, so in
         * the case of a device mapping a negative offset is passed
         * on.
         */
        if (
#ifdef _LP64
            size > OFF_MAX ||
#endif
            foff < 0 || foff > OFF_MAX - size)
                return (EINVAL);

        writecounted = FALSE;
        error = vm_mmap_vnode(td, size, prot, &maxprot, &flags, vp,
            &foff, &object, &writecounted);
        if (error != 0)
                return (error);
        error = vm_mmap_object(map, addr, size, prot, maxprot, flags, object,
            foff, writecounted, td);
        if (error != 0) {
                /*
                 * If this mapping was accounted for in the vnode's
                 * writecount, then undo that now.
                 */
                if (writecounted)
                        vm_pager_release_writecount(object, 0, size);
                vm_object_deallocate(object);
        }
#ifdef HWPMC_HOOKS
        /* Inform hwpmc(4) if an executable is being mapped. */
        if (PMC_HOOK_INSTALLED(PMC_FN_MMAP)) {
                if ((prot & VM_PROT_EXECUTE) != 0 && error == 0) {
                        pkm.pm_file = vp;
                        pkm.pm_address = (uintptr_t) *addr;
                        PMC_CALL_HOOK_UNLOCKED(td, PMC_FN_MMAP, (void *) &pkm);
                }
        }
#endif
        return (error);
}

void
vn_fsid(struct vnode *vp, struct vattr *va)
{
        fsid_t *f;

        f = &vp->v_mount->mnt_stat.f_fsid;
        va->va_fsid = (uint32_t)f->val[1];
        va->va_fsid <<= sizeof(f->val[1]) * NBBY;
        va->va_fsid += (uint32_t)f->val[0];
}

int
vn_fsync_buf(struct vnode *vp, int waitfor)
{
        struct buf *bp, *nbp;
        struct bufobj *bo;
        struct mount *mp;
        int error, maxretry;

        error = 0;
        maxretry = 10000;     /* large, arbitrarily chosen */
        mp = NULL;
        if (vp->v_type == VCHR) {
                VI_LOCK(vp);
                mp = vp->v_rdev->si_mountpt;
                VI_UNLOCK(vp);
        }
        bo = &vp->v_bufobj;
        BO_LOCK(bo);
loop1:
        /*
         * MARK/SCAN initialization to avoid infinite loops.
         */
        TAILQ_FOREACH(bp, &bo->bo_dirty.bv_hd, b_bobufs) {
                bp->b_vflags &= ~BV_SCANNED;
                bp->b_error = 0;
        }

        /*
         * Flush all dirty buffers associated with a vnode.
         */
loop2:
        TAILQ_FOREACH_SAFE(bp, &bo->bo_dirty.bv_hd, b_bobufs, nbp) {
                if ((bp->b_vflags & BV_SCANNED) != 0)
                        continue;
                bp->b_vflags |= BV_SCANNED;
                if (BUF_LOCK(bp, LK_EXCLUSIVE | LK_NOWAIT, NULL)) {
                        if (waitfor != MNT_WAIT)
                                continue;
                        if (BUF_LOCK(bp,
                            LK_EXCLUSIVE | LK_INTERLOCK | LK_SLEEPFAIL,
                            BO_LOCKPTR(bo)) != 0) {
                                BO_LOCK(bo);
                                goto loop1;
                        }
                        BO_LOCK(bo);
                }
                BO_UNLOCK(bo);
                KASSERT(bp->b_bufobj == bo,
                    ("bp %p wrong b_bufobj %p should be %p",
                    bp, bp->b_bufobj, bo));
                if ((bp->b_flags & B_DELWRI) == 0)
                        panic("fsync: not dirty");
                if ((vp->v_object != NULL) && (bp->b_flags & B_CLUSTEROK)) {
                        vfs_bio_awrite(bp);
                } else {
                        bremfree(bp);
                        bawrite(bp);
                }
                if (maxretry < 1000)
                        pause("dirty", hz < 1000 ? 1 : hz / 1000);
                BO_LOCK(bo);
                goto loop2;
        }

        /*
         * If synchronous the caller expects us to completely resolve all
         * dirty buffers in the system.  Wait for in-progress I/O to
         * complete (which could include background bitmap writes), then
         * retry if dirty blocks still exist.
         */
        if (waitfor == MNT_WAIT) {
                bufobj_wwait(bo, 0, 0);
                if (bo->bo_dirty.bv_cnt > 0) {
                        /*
                         * If we are unable to write any of these buffers
                         * then we fail now rather than trying endlessly
                         * to write them out.
                         */
                        TAILQ_FOREACH(bp, &bo->bo_dirty.bv_hd, b_bobufs)
                                if ((error = bp->b_error) != 0)
                                        break;
                        if ((mp != NULL && mp->mnt_secondary_writes > 0) ||
                            (error == 0 && --maxretry >= 0))
                                goto loop1;
                        if (error == 0)
                                error = EAGAIN;
                }
        }
        BO_UNLOCK(bo);
        if (error != 0)
                vn_printf(vp, "fsync: giving up on dirty (error = %d) ", error);

        return (error);
}

/*
 * Copies a byte range from invp to outvp.  Calls VOP_COPY_FILE_RANGE()
 * or vn_generic_copy_file_range() after rangelocking the byte ranges,
 * to do the actual copy.
 * vn_generic_copy_file_range() is factored out, so it can be called
 * from a VOP_COPY_FILE_RANGE() call as well, but handles vnodes from
 * different file systems.
 */
int
vn_copy_file_range(struct vnode *invp, off_t *inoffp, struct vnode *outvp,
    off_t *outoffp, size_t *lenp, unsigned int flags, struct ucred *incred,
    struct ucred *outcred, struct thread *fsize_td)
{
        int error;
        size_t len;
        uint64_t uvalin, uvalout;

        len = *lenp;
        *lenp = 0;              /* For error returns. */
        error = 0;

        /* Do some sanity checks on the arguments. */
        uvalin = *inoffp;
        uvalin += len;
        uvalout = *outoffp;
        uvalout += len;
        if (invp->v_type == VDIR || outvp->v_type == VDIR)
                error = EISDIR;
        else if (*inoffp < 0 || uvalin > INT64_MAX || uvalin <
            (uint64_t)*inoffp || *outoffp < 0 || uvalout > INT64_MAX ||
            uvalout < (uint64_t)*outoffp || invp->v_type != VREG ||
            outvp->v_type != VREG)
                error = EINVAL;
        if (error != 0)
                goto out;

        /*
         * If the two vnode are for the same file system, call
         * VOP_COPY_FILE_RANGE(), otherwise call vn_generic_copy_file_range()
         * which can handle copies across multiple file systems.
         */
        *lenp = len;
        if (invp->v_mount == outvp->v_mount)
                error = VOP_COPY_FILE_RANGE(invp, inoffp, outvp, outoffp,
                    lenp, flags, incred, outcred, fsize_td);
        else
                error = vn_generic_copy_file_range(invp, inoffp, outvp,
                    outoffp, lenp, flags, incred, outcred, fsize_td);
out:
        return (error);
}

/*
 * Test len bytes of data starting at dat for all bytes == 0.
 * Return true if all bytes are zero, false otherwise.
 * Expects dat to be well aligned.
 */
static bool
mem_iszero(void *dat, int len)
{
        int i;
        const u_int *p;
        const char *cp;

        for (p = dat; len > 0; len -= sizeof(*p), p++) {
                if (len >= sizeof(*p)) {
                        if (*p != 0)
                                return (false);
                } else {
                        cp = (const char *)p;
                        for (i = 0; i < len; i++, cp++)
                                if (*cp != '\0')
                                        return (false);
                }
        }
        return (true);
}

/*
 * Look for a hole in the output file and, if found, adjust *outoffp
 * and *xferp to skip past the hole.
 * *xferp is the entire hole length to be written and xfer2 is how many bytes
 * to be written as 0's upon return.
 */
static off_t
vn_skip_hole(struct vnode *outvp, off_t xfer2, off_t *outoffp, off_t *xferp,
    off_t *dataoffp, off_t *holeoffp, struct ucred *cred)
{
        int error;
        off_t delta;

        if (*holeoffp == 0 || *holeoffp <= *outoffp) {
                *dataoffp = *outoffp;
                error = VOP_IOCTL(outvp, FIOSEEKDATA, dataoffp, 0, cred,
                    curthread);
                if (error == 0) {
                        *holeoffp = *dataoffp;
                        error = VOP_IOCTL(outvp, FIOSEEKHOLE, holeoffp, 0, cred,
                            curthread);
                }
                if (error != 0 || *holeoffp == *dataoffp) {
                        /*
                         * Since outvp is unlocked, it may be possible for
                         * another thread to do a truncate(), lseek(), write()
                         * creating a hole at startoff between the above
                         * VOP_IOCTL() calls, if the other thread does not do
                         * rangelocking.
                         * If that happens, *holeoffp == *dataoffp and finding
                         * the hole has failed, so disable vn_skip_hole().
                         */
                        *holeoffp = -1; /* Disable use of vn_skip_hole(). */
                        return (xfer2);
                }
                KASSERT(*dataoffp >= *outoffp,
                    ("vn_skip_hole: dataoff=%jd < outoff=%jd",
                    (intmax_t)*dataoffp, (intmax_t)*outoffp));
                KASSERT(*holeoffp > *dataoffp,
                    ("vn_skip_hole: holeoff=%jd <= dataoff=%jd",
                    (intmax_t)*holeoffp, (intmax_t)*dataoffp));
        }

        /*
         * If there is a hole before the data starts, advance *outoffp and
         * *xferp past the hole.
         */
        if (*dataoffp > *outoffp) {
                delta = *dataoffp - *outoffp;
                if (delta >= *xferp) {
                        /* Entire *xferp is a hole. */
                        *outoffp += *xferp;
                        *xferp = 0;
                        return (0);
                }
                *xferp -= delta;
                *outoffp += delta;
                xfer2 = MIN(xfer2, *xferp);
        }

        /*
         * If a hole starts before the end of this xfer2, reduce this xfer2 so
         * that the write ends at the start of the hole.
         * *holeoffp should always be greater than *outoffp, but for the
         * non-INVARIANTS case, check this to make sure xfer2 remains a sane
         * value.
         */
        if (*holeoffp > *outoffp && *holeoffp < *outoffp + xfer2)
                xfer2 = *holeoffp - *outoffp;
        return (xfer2);
}

/*
 * Write an xfer sized chunk to outvp in blksize blocks from dat.
 * dat is a maximum of blksize in length and can be written repeatedly in
 * the chunk.
 * If growfile == true, just grow the file via vn_truncate_locked() instead
 * of doing actual writes.
 * If checkhole == true, a hole is being punched, so skip over any hole
 * already in the output file.
 */
static int
vn_write_outvp(struct vnode *outvp, char *dat, off_t outoff, off_t xfer,
    u_long blksize, bool growfile, bool checkhole, struct ucred *cred)
{
        struct mount *mp;
        off_t dataoff, holeoff, xfer2;
        int error, lckf;

        /*
         * Loop around doing writes of blksize until write has been completed.
         * Lock/unlock on each loop iteration so that a bwillwrite() can be
         * done for each iteration, since the xfer argument can be very
         * large if there is a large hole to punch in the output file.
         */
        error = 0;
        holeoff = 0;
        do {
                xfer2 = MIN(xfer, blksize);
                if (checkhole) {
                        /*
                         * Punching a hole.  Skip writing if there is
                         * already a hole in the output file.
                         */
                        xfer2 = vn_skip_hole(outvp, xfer2, &outoff, &xfer,
                            &dataoff, &holeoff, cred);
                        if (xfer == 0)
                                break;
                        if (holeoff < 0)
                                checkhole = false;
                        KASSERT(xfer2 > 0, ("vn_write_outvp: xfer2=%jd",
                            (intmax_t)xfer2));
                }
                bwillwrite();
                mp = NULL;
                error = vn_start_write(outvp, &mp, V_WAIT);
                if (error == 0) {
                        if (MNT_SHARED_WRITES(mp))
                                lckf = LK_SHARED;
                        else
                                lckf = LK_EXCLUSIVE;
                        error = vn_lock(outvp, lckf);
                }
                if (error == 0) {
                        if (growfile)
                                error = vn_truncate_locked(outvp, outoff + xfer,
                                    false, cred);
                        else {
                                error = vn_rdwr(UIO_WRITE, outvp, dat, xfer2,
                                    outoff, UIO_SYSSPACE, IO_NODELOCKED,
                                    curthread->td_ucred, cred, NULL, curthread);
                                outoff += xfer2;
                                xfer -= xfer2;
                        }
                        VOP_UNLOCK(outvp);
                }
                if (mp != NULL)
                        vn_finished_write(mp);
        } while (!growfile && xfer > 0 && error == 0);
        return (error);
}

/*
 * Copy a byte range of one file to another.  This function can handle the
 * case where invp and outvp are on different file systems.
 * It can also be called by a VOP_COPY_FILE_RANGE() to do the work, if there
 * is no better file system specific way to do it.
 */
int
vn_generic_copy_file_range(struct vnode *invp, off_t *inoffp,
    struct vnode *outvp, off_t *outoffp, size_t *lenp, unsigned int flags,
    struct ucred *incred, struct ucred *outcred, struct thread *fsize_td)
{
        struct vattr va;
        struct mount *mp;
        struct uio io;
        off_t startoff, endoff, xfer, xfer2;
        u_long blksize;
        int error;
        bool cantseek, readzeros, eof, lastblock;
        ssize_t aresid;
        size_t copylen, len, savlen;
        char *dat;
        long holein, holeout;

        holein = holeout = 0;
        savlen = len = *lenp;
        error = 0;
        dat = NULL;

        error = vn_lock(invp, LK_SHARED);
        if (error != 0)
                goto out;
        if (VOP_PATHCONF(invp, _PC_MIN_HOLE_SIZE, &holein) != 0)
                holein = 0;
        VOP_UNLOCK(invp);

        mp = NULL;
        error = vn_start_write(outvp, &mp, V_WAIT);
        if (error == 0)
                error = vn_lock(outvp, LK_EXCLUSIVE);
        if (error == 0) {
                /*
                 * If fsize_td != NULL, do a vn_rlimit_fsize() call,
                 * now that outvp is locked.
                 */
                if (fsize_td != NULL) {
                        io.uio_offset = *outoffp;
                        io.uio_resid = len;
                        error = vn_rlimit_fsize(outvp, &io, fsize_td);
                        if (error != 0)
                                error = EFBIG;
                }
                if (VOP_PATHCONF(outvp, _PC_MIN_HOLE_SIZE, &holeout) != 0)
                        holeout = 0;
                /*
                 * Holes that are past EOF do not need to be written as a block
                 * of zero bytes.  So, truncate the output file as far as
                 * possible and then use va.va_size to decide if writing 0
                 * bytes is necessary in the loop below.
                 */
                if (error == 0)
                        error = VOP_GETATTR(outvp, &va, outcred);
                if (error == 0 && va.va_size > *outoffp && va.va_size <=
                    *outoffp + len) {
#ifdef MAC
                        error = mac_vnode_check_write(curthread->td_ucred,
                            outcred, outvp);
                        if (error == 0)
#endif
                                error = vn_truncate_locked(outvp, *outoffp,
                                    false, outcred);
                        if (error == 0)
                                va.va_size = *outoffp;
                }
                VOP_UNLOCK(outvp);
        }
        if (mp != NULL)
                vn_finished_write(mp);
        if (error != 0)
                goto out;

        /*
         * Set the blksize to the larger of the hole sizes for invp and outvp.
         * If hole sizes aren't available, set the blksize to the larger 
         * f_iosize of invp and outvp.
         * This code expects the hole sizes and f_iosizes to be powers of 2.
         * This value is clipped at 4Kbytes and 1Mbyte.
         */
        blksize = MAX(holein, holeout);
        if (blksize == 0)
                blksize = MAX(invp->v_mount->mnt_stat.f_iosize,
                    outvp->v_mount->mnt_stat.f_iosize);
        if (blksize < 4096)
                blksize = 4096;
        else if (blksize > 1024 * 1024)
                blksize = 1024 * 1024;
        dat = malloc(blksize, M_TEMP, M_WAITOK);

        /*
         * If VOP_IOCTL(FIOSEEKHOLE) works for invp, use it and FIOSEEKDATA
         * to find holes.  Otherwise, just scan the read block for all 0s
         * in the inner loop where the data copying is done.
         * Note that some file systems such as NFSv3, NFSv4.0 and NFSv4.1 may
         * support holes on the server, but do not support FIOSEEKHOLE.
         */
        eof = false;
        while (len > 0 && error == 0 && !eof) {
                endoff = 0;                     /* To shut up compilers. */
                cantseek = true;
                startoff = *inoffp;
                copylen = len;

                /*
                 * Find the next data area.  If there is just a hole to EOF,
                 * FIOSEEKDATA should fail and then we drop down into the
                 * inner loop and create the hole on the outvp file.
                 * (I do not know if any file system will report a hole to
                 *  EOF via FIOSEEKHOLE, but I am pretty sure FIOSEEKDATA
                 *  will fail for those file systems.)
                 *
                 * For input files that don't support FIOSEEKDATA/FIOSEEKHOLE,
                 * the code just falls through to the inner copy loop.
                 */
                error = EINVAL;
                if (holein > 0)
                        error = VOP_IOCTL(invp, FIOSEEKDATA, &startoff, 0,
                            incred, curthread);
                if (error == 0) {
                        endoff = startoff;
                        error = VOP_IOCTL(invp, FIOSEEKHOLE, &endoff, 0,
                            incred, curthread);
                        /*
                         * Since invp is unlocked, it may be possible for
                         * another thread to do a truncate(), lseek(), write()
                         * creating a hole at startoff between the above
                         * VOP_IOCTL() calls, if the other thread does not do
                         * rangelocking.
                         * If that happens, startoff == endoff and finding
                         * the hole has failed, so set an error.
                         */
                        if (error == 0 && startoff == endoff)
                                error = EINVAL; /* Any error. Reset to 0. */
                }
                if (error == 0) {
                        if (startoff > *inoffp) {
                                /* Found hole before data block. */
                                xfer = MIN(startoff - *inoffp, len);
                                if (*outoffp < va.va_size) {
                                        /* Must write 0s to punch hole. */
                                        xfer2 = MIN(va.va_size - *outoffp,
                                            xfer);
                                        memset(dat, 0, MIN(xfer2, blksize));
                                        error = vn_write_outvp(outvp, dat,
                                            *outoffp, xfer2, blksize, false,
                                            holeout > 0, outcred);
                                }

                                if (error == 0 && *outoffp + xfer >
                                    va.va_size && xfer == len)
                                        /* Grow last block. */
                                        error = vn_write_outvp(outvp, dat,
                                            *outoffp, xfer, blksize, true,
                                            false, outcred);
                                if (error == 0) {
                                        *inoffp += xfer;
                                        *outoffp += xfer;
                                        len -= xfer;
                                }
                        }
                        copylen = MIN(len, endoff - startoff);
                        cantseek = false;
                } else {
                        cantseek = true;
                        startoff = *inoffp;
                        copylen = len;
                        error = 0;
                }

                xfer = blksize;
                if (cantseek) {
                        /*
                         * Set first xfer to end at a block boundary, so that
                         * holes are more likely detected in the loop below via
                         * the for all bytes 0 method.
                         */
                        xfer -= (*inoffp % blksize);
                }
                /* Loop copying the data block. */
                while (copylen > 0 && error == 0 && !eof) {
                        if (copylen < xfer)
                                xfer = copylen;
                        error = vn_lock(invp, LK_SHARED);
                        if (error != 0)
                                goto out;
                        error = vn_rdwr(UIO_READ, invp, dat, xfer,
                            startoff, UIO_SYSSPACE, IO_NODELOCKED,
                            curthread->td_ucred, incred, &aresid,
                            curthread);
                        VOP_UNLOCK(invp);
                        lastblock = false;
                        if (error == 0 && aresid > 0) {
                                /* Stop the copy at EOF on the input file. */
                                xfer -= aresid;
                                eof = true;
                                lastblock = true;
                        }
                        if (error == 0) {
                                /*
                                 * Skip the write for holes past the initial EOF
                                 * of the output file, unless this is the last
                                 * write of the output file at EOF.
                                 */
                                readzeros = cantseek ? mem_iszero(dat, xfer) :
                                    false;
                                if (xfer == len)
                                        lastblock = true;
                                if (!cantseek || *outoffp < va.va_size ||
                                    lastblock || !readzeros)
                                        error = vn_write_outvp(outvp, dat,
                                            *outoffp, xfer, blksize,
                                            readzeros && lastblock &&
                                            *outoffp >= va.va_size, false,
                                            outcred);
                                if (error == 0) {
                                        *inoffp += xfer;
                                        startoff += xfer;
                                        *outoffp += xfer;
                                        copylen -= xfer;
                                        len -= xfer;
                                }
                        }
                        xfer = blksize;
                }
        }
out:
        *lenp = savlen - len;
        free(dat, M_TEMP);
        return (error);
}

static int
vn_fallocate(struct file *fp, off_t offset, off_t len, struct thread *td)
{
        struct mount *mp;
        struct vnode *vp;
        off_t olen, ooffset;
        int error;
#ifdef AUDIT
        int audited_vnode1 = 0;
#endif

        vp = fp->f_vnode;
        if (vp->v_type != VREG)
                return (ENODEV);

        /* Allocating blocks may take a long time, so iterate. */
        for (;;) {
                olen = len;
                ooffset = offset;

                bwillwrite();
                mp = NULL;
                error = vn_start_write(vp, &mp, V_WAIT | PCATCH);
                if (error != 0)
                        break;
                error = vn_lock(vp, LK_EXCLUSIVE);
                if (error != 0) {
                        vn_finished_write(mp);
                        break;
                }
#ifdef AUDIT
                if (!audited_vnode1) {
                        AUDIT_ARG_VNODE1(vp);
                        audited_vnode1 = 1;
                }
#endif
#ifdef MAC
                error = mac_vnode_check_write(td->td_ucred, fp->f_cred, vp);
                if (error == 0)
#endif
                        error = VOP_ALLOCATE(vp, &offset, &len);
                VOP_UNLOCK(vp);
                vn_finished_write(mp);

                if (olen + ooffset != offset + len) {
                        panic("offset + len changed from %jx/%jx to %jx/%jx",
                            ooffset, olen, offset, len);
                }
                if (error != 0 || len == 0)
                        break;
                KASSERT(olen > len, ("Iteration did not make progress?"));
                maybe_yield();
        }

        return (error);
}