Merge branch 'releng/11.3' into releng-CDN/11.3

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

/*-
 * Copyright (c) 2013-2015 Gleb Smirnoff <glebius@FreeBSD.org>
 * Copyright (c) 1998, David Greenman. All rights reserved.
 *
 * 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.
 * 4. 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.
 */

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

#include "opt_compat.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/capsicum.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/sysproto.h>
#include <sys/malloc.h>
#include <sys/proc.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/rwlock.h>
#include <sys/sf_buf.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/syscallsubr.h>
#include <sys/sysctl.h>
#include <sys/vnode.h>

#include <net/vnet.h>

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

#include <vm/vm.h>
#include <vm/vm_object.h>
#include <vm/vm_pager.h>

/*
 * Structure describing a single sendfile(2) I/O, which may consist of
 * several underlying pager I/Os.
 *
 * The syscall context allocates the structure and initializes 'nios'
 * to 1.  As sendfile_swapin() runs through pages and starts asynchronous
 * paging operations, it increments 'nios'.
 *
 * Every I/O completion calls sendfile_iodone(), which decrements the 'nios',
 * and the syscall also calls sendfile_iodone() after allocating all mbufs,
 * linking them and sending to socket.  Whoever reaches zero 'nios' is
 * responsible to * call pru_ready on the socket, to notify it of readyness
 * of the data.
 */
struct sf_io {
        volatile u_int  nios;
        u_int           error;
        int             npages;
        struct file     *sock_fp;
        struct mbuf     *m;
        vm_page_t       pa[];
};

/*
 * Structure used to track requests with SF_SYNC flag.
 */
struct sendfile_sync {
        struct mtx      mtx;
        struct cv       cv;
        unsigned        count;
};

counter_u64_t sfstat[sizeof(struct sfstat) / sizeof(uint64_t)];

static void
sfstat_init(const void *unused)
{

        COUNTER_ARRAY_ALLOC(sfstat, sizeof(struct sfstat) / sizeof(uint64_t),
            M_WAITOK);
}
SYSINIT(sfstat, SI_SUB_MBUF, SI_ORDER_FIRST, sfstat_init, NULL);

static int
sfstat_sysctl(SYSCTL_HANDLER_ARGS)
{
        struct sfstat s;

        COUNTER_ARRAY_COPY(sfstat, &s, sizeof(s) / sizeof(uint64_t));
        if (req->newptr)
                COUNTER_ARRAY_ZERO(sfstat, sizeof(s) / sizeof(uint64_t));
        return (SYSCTL_OUT(req, &s, sizeof(s)));
}
SYSCTL_PROC(_kern_ipc, OID_AUTO, sfstat, CTLTYPE_OPAQUE | CTLFLAG_RW,
    NULL, 0, sfstat_sysctl, "I", "sendfile statistics");

/*
 * Detach mapped page and release resources back to the system.  Called
 * by mbuf(9) code when last reference to a page is freed.
 */
void
sf_ext_free(void *arg1, void *arg2)
{
        struct sf_buf *sf = arg1;
        struct sendfile_sync *sfs = arg2;
        vm_page_t pg = sf_buf_page(sf);

        sf_buf_free(sf);

        vm_page_lock(pg);
        /*
         * Check for the object going away on us. This can
         * happen since we don't hold a reference to it.
         * If so, we're responsible for freeing the page.
         */
        if (vm_page_unwire(pg, PQ_INACTIVE) && pg->object == NULL)
                vm_page_free(pg);
        vm_page_unlock(pg);

        if (sfs != NULL) {
                mtx_lock(&sfs->mtx);
                KASSERT(sfs->count > 0, ("Sendfile sync botchup count == 0"));
                if (--sfs->count == 0)
                        cv_signal(&sfs->cv);
                mtx_unlock(&sfs->mtx);
        }
}

/*
 * Same as above, but forces the page to be detached from the object
 * and go into free pool.
 */
void
sf_ext_free_nocache(void *arg1, void *arg2)
{
        struct sf_buf *sf = arg1;
        struct sendfile_sync *sfs = arg2;
        vm_page_t pg = sf_buf_page(sf);

        sf_buf_free(sf);

        vm_page_lock(pg);
        if (vm_page_unwire(pg, PQ_NONE)) {
                vm_object_t obj;

                /* Try to free the page, but only if it is cheap to. */
                if ((obj = pg->object) == NULL)
                        vm_page_free(pg);
                else if (!vm_page_xbusied(pg) && VM_OBJECT_TRYWLOCK(obj)) {
                        vm_page_free(pg);
                        VM_OBJECT_WUNLOCK(obj);
                } else
                        vm_page_deactivate(pg);
        }
        vm_page_unlock(pg);

        if (sfs != NULL) {
                mtx_lock(&sfs->mtx);
                KASSERT(sfs->count > 0, ("Sendfile sync botchup count == 0"));
                if (--sfs->count == 0)
                        cv_signal(&sfs->cv);
                mtx_unlock(&sfs->mtx);
        }
}

/*
 * Helper function to calculate how much data to put into page i of n.
 * Only first and last pages are special.
 */
static inline off_t
xfsize(int i, int n, off_t off, off_t len)
{

        if (i == 0)
                return (omin(PAGE_SIZE - (off & PAGE_MASK), len));

        if (i == n - 1 && ((off + len) & PAGE_MASK) > 0)
                return ((off + len) & PAGE_MASK);

        return (PAGE_SIZE);
}

/*
 * Helper function to get offset within object for i page.
 */
static inline vm_ooffset_t
vmoff(int i, off_t off)
{

        if (i == 0)
                return ((vm_ooffset_t)off);

        return (trunc_page(off + i * PAGE_SIZE));
}

/*
 * Helper function used when allocation of a page or sf_buf failed.
 * Pretend as if we don't have enough space, subtract xfsize() of
 * all pages that failed.
 */
static inline void
fixspace(int old, int new, off_t off, int *space)
{

        KASSERT(old > new, ("%s: old %d new %d", __func__, old, new));

        /* Subtract last one. */
        *space -= xfsize(old - 1, old, off, *space);
        old--;

        if (new == old)
                /* There was only one page. */
                return;

        /* Subtract first one. */
        if (new == 0) {
                *space -= xfsize(0, old, off, *space);
                new++;
        }

        /* Rest of pages are full sized. */
        *space -= (old - new) * PAGE_SIZE;

        KASSERT(*space >= 0, ("%s: space went backwards", __func__));
}

/*
 * I/O completion callback.
 */
static void
sendfile_iodone(void *arg, vm_page_t *pg, int count, int error)
{
        struct sf_io *sfio = arg;
        struct socket *so;

        for (int i = 0; i < count; i++)
                vm_page_xunbusy(pg[i]);

        if (error)
                sfio->error = error;

        if (!refcount_release(&sfio->nios))
                return;

        so = sfio->sock_fp->f_data;

        if (sfio->error) {
                struct mbuf *m;

                /*
                 * I/O operation failed.  The state of data in the socket
                 * is now inconsistent, and all what we can do is to tear
                 * it down. Protocol abort method would tear down protocol
                 * state, free all ready mbufs and detach not ready ones.
                 * We will free the mbufs corresponding to this I/O manually.
                 *
                 * The socket would be marked with EIO and made available
                 * for read, so that application receives EIO on next
                 * syscall and eventually closes the socket.
                 */
                so->so_proto->pr_usrreqs->pru_abort(so);
                so->so_error = EIO;

                m = sfio->m;
                for (int i = 0; i < sfio->npages; i++)
                        m = m_free(m);
        } else {
                CURVNET_SET(so->so_vnet);
                (void )(so->so_proto->pr_usrreqs->pru_ready)(so, sfio->m,
                    sfio->npages);
                CURVNET_RESTORE();
        }

        /* XXXGL: curthread */
        fdrop(sfio->sock_fp, curthread);
        free(sfio, M_TEMP);
}

/*
 * Iterate through pages vector and request paging for non-valid pages.
 */
static int
sendfile_swapin(vm_object_t obj, struct sf_io *sfio, off_t off, off_t len,
    int npages, int rhpages, int flags)
{
        vm_page_t *pa = sfio->pa;
        int grabbed, nios;

        nios = 0;
        flags = (flags & SF_NODISKIO) ? VM_ALLOC_NOWAIT : 0;

        /*
         * First grab all the pages and wire them.  Note that we grab
         * only required pages.  Readahead pages are dealt with later.
         */
        VM_OBJECT_WLOCK(obj);

        grabbed = vm_page_grab_pages(obj, OFF_TO_IDX(off),
            VM_ALLOC_NORMAL | VM_ALLOC_WIRED | flags, pa, npages);
        if (grabbed < npages) {
                for (int i = grabbed; i < npages; i++)
                        pa[i] = NULL;
                npages = grabbed;
                rhpages = 0;
        }

        for (int i = 0; i < npages;) {
                int j, a, count, rv;

                /* Skip valid pages. */
                if (vm_page_is_valid(pa[i], vmoff(i, off) & PAGE_MASK,
                    xfsize(i, npages, off, len))) {
                        vm_page_xunbusy(pa[i]);
                        SFSTAT_INC(sf_pages_valid);
                        i++;
                        continue;
                }

                /*
                 * Now 'i' points to first invalid page, iterate further
                 * to make 'j' point at first valid after a bunch of
                 * invalid ones.
                 */
                for (j = i + 1; j < npages; j++)
                        if (vm_page_is_valid(pa[j], vmoff(j, off) & PAGE_MASK,
                            xfsize(j, npages, off, len))) {
                                SFSTAT_INC(sf_pages_valid);
                                break;
                        }

                /*
                 * Now we got region of invalid pages between 'i' and 'j'.
                 * Check that they belong to pager.  They may not be there,
                 * which is a regular situation for shmem pager.  For vnode
                 * pager this happens only in case of sparse file.
                 *
                 * Important feature of vm_pager_has_page() is the hint
                 * stored in 'a', about how many pages we can pagein after
                 * this page in a single I/O.
                 */
                while (!vm_pager_has_page(obj, OFF_TO_IDX(vmoff(i, off)),
                    NULL, &a) && i < j) {
                        pmap_zero_page(pa[i]);
                        pa[i]->valid = VM_PAGE_BITS_ALL;
                        MPASS(pa[i]->dirty == 0);
                        vm_page_xunbusy(pa[i]);
                        i++;
                }
                if (i == j)
                        continue;

                /*
                 * We want to pagein as many pages as possible, limited only
                 * by the 'a' hint and actual request.
                 *
                 * We should not pagein into already valid page, thus if
                 * 'j' didn't reach last page, trim by that page.
                 *
                 * When the pagein fulfils the request, also specify readahead.
                 */
                if (j < npages)
                        a = min(a, j - i - 1);
                count = min(a + 1, npages - i);

                refcount_acquire(&sfio->nios);
                rv = vm_pager_get_pages_async(obj, pa + i, count, NULL,
                    i + count == npages ? &rhpages : NULL,
                    &sendfile_iodone, sfio);
                KASSERT(rv == VM_PAGER_OK, ("%s: pager fail obj %p page %p",
                    __func__, obj, pa[i]));

                SFSTAT_INC(sf_iocnt);
                SFSTAT_ADD(sf_pages_read, count);
                if (i + count == npages)
                        SFSTAT_ADD(sf_rhpages_read, rhpages);

#ifdef INVARIANTS
                for (j = i; j < i + count && j < npages; j++)
                        KASSERT(pa[j] == vm_page_lookup(obj,
                            OFF_TO_IDX(vmoff(j, off))),
                            ("pa[j] %p lookup %p\n", pa[j],
                            vm_page_lookup(obj, OFF_TO_IDX(vmoff(j, off)))));
#endif
                i += count;
                nios++;
        }

        VM_OBJECT_WUNLOCK(obj);

        if (nios == 0 && npages != 0)
                SFSTAT_INC(sf_noiocnt);

        return (nios);
}

static int
sendfile_getobj(struct thread *td, struct file *fp, vm_object_t *obj_res,
    struct vnode **vp_res, struct shmfd **shmfd_res, off_t *obj_size,
    int *bsize)
{
        struct vattr va;
        vm_object_t obj;
        struct vnode *vp;
        struct shmfd *shmfd;
        int error;

        vp = *vp_res = NULL;
        obj = NULL;
        shmfd = *shmfd_res = NULL;
        *bsize = 0;

        /*
         * The file descriptor must be a regular file and have a
         * backing VM object.
         */
        if (fp->f_type == DTYPE_VNODE) {
                vp = fp->f_vnode;
                vn_lock(vp, LK_SHARED | LK_RETRY);
                if (vp->v_type != VREG) {
                        error = EINVAL;
                        goto out;
                }
                *bsize = vp->v_mount->mnt_stat.f_iosize;
                error = VOP_GETATTR(vp, &va, td->td_ucred);
                if (error != 0)
                        goto out;
                *obj_size = va.va_size;
                obj = vp->v_object;
                if (obj == NULL) {
                        error = EINVAL;
                        goto out;
                }
        } else if (fp->f_type == DTYPE_SHM) {
                error = 0;
                shmfd = fp->f_data;
                obj = shmfd->shm_object;
                *obj_size = shmfd->shm_size;
        } else {
                error = EINVAL;
                goto out;
        }

        VM_OBJECT_WLOCK(obj);
        if ((obj->flags & OBJ_DEAD) != 0) {
                VM_OBJECT_WUNLOCK(obj);
                error = EBADF;
                goto out;
        }

        /*
         * Temporarily increase the backing VM object's reference
         * count so that a forced reclamation of its vnode does not
         * immediately destroy it.
         */
        vm_object_reference_locked(obj);
        VM_OBJECT_WUNLOCK(obj);
        *obj_res = obj;
        *vp_res = vp;
        *shmfd_res = shmfd;

out:
        if (vp != NULL)
                VOP_UNLOCK(vp, 0);
        return (error);
}

static int
sendfile_getsock(struct thread *td, int s, struct file **sock_fp,
    struct socket **so)
{
        cap_rights_t rights;
        int error;

        *sock_fp = NULL;
        *so = NULL;

        /*
         * The socket must be a stream socket and connected.
         */
        error = getsock_cap(td, s, cap_rights_init(&rights, CAP_SEND),
            sock_fp, NULL, NULL);
        if (error != 0)
                return (error);
        *so = (*sock_fp)->f_data;
        if ((*so)->so_type != SOCK_STREAM)
                return (EINVAL);
        if (((*so)->so_state & SS_ISCONNECTED) == 0)
                return (ENOTCONN);
        return (0);
}

int
vn_sendfile(struct file *fp, int sockfd, struct uio *hdr_uio,
    struct uio *trl_uio, off_t offset, size_t nbytes, off_t *sent, int flags,
    struct thread *td)
{
        struct file *sock_fp;
        struct vnode *vp;
        struct vm_object *obj;
        struct socket *so;
        struct mbuf *m, *mh, *mhtail;
        struct sf_buf *sf;
        struct shmfd *shmfd;
        struct sendfile_sync *sfs;
        struct vattr va;
        off_t off, sbytes, rem, obj_size;
        int error, softerr, bsize, hdrlen;

        obj = NULL;
        so = NULL;
        m = mh = NULL;
        sfs = NULL;
        hdrlen = sbytes = 0;
        softerr = 0;

        error = sendfile_getobj(td, fp, &obj, &vp, &shmfd, &obj_size, &bsize);
        if (error != 0)
                return (error);

        error = sendfile_getsock(td, sockfd, &sock_fp, &so);
        if (error != 0)
                goto out;

#ifdef MAC
        error = mac_socket_check_send(td->td_ucred, so);
        if (error != 0)
                goto out;
#endif

        SFSTAT_INC(sf_syscalls);
        SFSTAT_ADD(sf_rhpages_requested, SF_READAHEAD(flags));

        if (flags & SF_SYNC) {
                sfs = malloc(sizeof *sfs, M_TEMP, M_WAITOK | M_ZERO);
                mtx_init(&sfs->mtx, "sendfile", NULL, MTX_DEF);
                cv_init(&sfs->cv, "sendfile");
        }

        rem = nbytes ? omin(nbytes, obj_size - offset) : obj_size - offset;

        /*
         * Protect against multiple writers to the socket.
         *
         * XXXRW: Historically this has assumed non-interruptibility, so now
         * we implement that, but possibly shouldn't.
         */
        (void)sblock(&so->so_snd, SBL_WAIT | SBL_NOINTR);

        /*
         * Loop through the pages of the file, starting with the requested
         * offset. Get a file page (do I/O if necessary), map the file page
         * into an sf_buf, attach an mbuf header to the sf_buf, and queue
         * it on the socket.
         * This is done in two loops.  The inner loop turns as many pages
         * as it can, up to available socket buffer space, without blocking
         * into mbufs to have it bulk delivered into the socket send buffer.
         * The outer loop checks the state and available space of the socket
         * and takes care of the overall progress.
         */
        for (off = offset; rem > 0; ) {
                struct sf_io *sfio;
                vm_page_t *pa;
                struct mbuf *mtail;
                int nios, space, npages, rhpages;

                mtail = NULL;
                /*
                 * Check the socket state for ongoing connection,
                 * no errors and space in socket buffer.
                 * If space is low allow for the remainder of the
                 * file to be processed if it fits the socket buffer.
                 * Otherwise block in waiting for sufficient space
                 * to proceed, or if the socket is nonblocking, return
                 * to userland with EAGAIN while reporting how far
                 * we've come.
                 * We wait until the socket buffer has significant free
                 * space to do bulk sends.  This makes good use of file
                 * system read ahead and allows packet segmentation
                 * offloading hardware to take over lots of work.  If
                 * we were not careful here we would send off only one
                 * sfbuf at a time.
                 */
                SOCKBUF_LOCK(&so->so_snd);
                if (so->so_snd.sb_lowat < so->so_snd.sb_hiwat / 2)
                        so->so_snd.sb_lowat = so->so_snd.sb_hiwat / 2;
retry_space:
                if (so->so_snd.sb_state & SBS_CANTSENDMORE) {
                        error = EPIPE;
                        SOCKBUF_UNLOCK(&so->so_snd);
                        goto done;
                } else if (so->so_error) {
                        error = so->so_error;
                        so->so_error = 0;
                        SOCKBUF_UNLOCK(&so->so_snd);
                        goto done;
                }
                space = sbspace(&so->so_snd);
                if (space < rem &&
                    (space <= 0 ||
                     space < so->so_snd.sb_lowat)) {
                        if (so->so_state & SS_NBIO) {
                                SOCKBUF_UNLOCK(&so->so_snd);
                                error = EAGAIN;
                                goto done;
                        }
                        /*
                         * sbwait drops the lock while sleeping.
                         * When we loop back to retry_space the
                         * state may have changed and we retest
                         * for it.
                         */
                        error = sbwait(&so->so_snd);
                        /*
                         * An error from sbwait usually indicates that we've
                         * been interrupted by a signal. If we've sent anything
                         * then return bytes sent, otherwise return the error.
                         */
                        if (error != 0) {
                                SOCKBUF_UNLOCK(&so->so_snd);
                                goto done;
                        }
                        goto retry_space;
                }
                SOCKBUF_UNLOCK(&so->so_snd);

                /*
                 * At the beginning of the first loop check if any headers
                 * are specified and copy them into mbufs.  Reduce space in
                 * the socket buffer by the size of the header mbuf chain.
                 * Clear hdr_uio here and hdrlen at the end of the first loop.
                 */
                if (hdr_uio != NULL && hdr_uio->uio_resid > 0) {
                        hdr_uio->uio_td = td;
                        hdr_uio->uio_rw = UIO_WRITE;
                        mh = m_uiotombuf(hdr_uio, M_WAITOK, space, 0, 0);
                        hdrlen = m_length(mh, &mhtail);
                        space -= hdrlen;
                        /*
                         * If header consumed all the socket buffer space,
                         * don't waste CPU cycles and jump to the end.
                         */
                        if (space == 0) {
                                sfio = NULL;
                                nios = 0;
                                goto prepend_header;
                        }
                        hdr_uio = NULL;
                }

                if (vp != NULL) {
                        error = vn_lock(vp, LK_SHARED);
                        if (error != 0)
                                goto done;
                        error = VOP_GETATTR(vp, &va, td->td_ucred);
                        if (error != 0 || off >= va.va_size) {
                                VOP_UNLOCK(vp, 0);
                                goto done;
                        }
                        if (va.va_size != obj_size) {
                                obj_size = va.va_size;
                                rem = nbytes ?
                                    omin(nbytes + offset, obj_size) : obj_size;
                                rem -= off;
                        }
                }

                if (space > rem)
                        space = rem;

                npages = howmany(space + (off & PAGE_MASK), PAGE_SIZE);

                /*
                 * Calculate maximum allowed number of pages for readahead
                 * at this iteration.  First, we allow readahead up to "rem".
                 * If application wants more, let it be, but there is no
                 * reason to go above MAXPHYS.  Also check against "obj_size",
                 * since vm_pager_has_page() can hint beyond EOF.
                 */
                rhpages = howmany(rem + (off & PAGE_MASK), PAGE_SIZE) - npages;
                rhpages += SF_READAHEAD(flags);
                rhpages = min(howmany(MAXPHYS, PAGE_SIZE), rhpages);
                rhpages = min(howmany(obj_size - trunc_page(off), PAGE_SIZE) -
                    npages, rhpages);

                sfio = malloc(sizeof(struct sf_io) +
                    npages * sizeof(vm_page_t), M_TEMP, M_WAITOK);
                refcount_init(&sfio->nios, 1);
                sfio->error = 0;

                nios = sendfile_swapin(obj, sfio, off, space, npages, rhpages,
                    flags);

                /*
                 * Loop and construct maximum sized mbuf chain to be bulk
                 * dumped into socket buffer.
                 */
                pa = sfio->pa;
                for (int i = 0; i < npages; i++) {
                        struct mbuf *m0;

                        /*
                         * If a page wasn't grabbed successfully, then
                         * trim the array. Can happen only with SF_NODISKIO.
                         */
                        if (pa[i] == NULL) {
                                SFSTAT_INC(sf_busy);
                                fixspace(npages, i, off, &space);
                                npages = i;
                                softerr = EBUSY;
                                break;
                        }

                        /*
                         * Get a sendfile buf.  When allocating the
                         * first buffer for mbuf chain, we usually
                         * wait as long as necessary, but this wait
                         * can be interrupted.  For consequent
                         * buffers, do not sleep, since several
                         * threads might exhaust the buffers and then
                         * deadlock.
                         */
                        sf = sf_buf_alloc(pa[i],
                            m != NULL ? SFB_NOWAIT : SFB_CATCH);
                        if (sf == NULL) {
                                SFSTAT_INC(sf_allocfail);
                                for (int j = i; j < npages; j++) {
                                        vm_page_lock(pa[j]);
                                        vm_page_unwire(pa[j], PQ_INACTIVE);
                                        vm_page_unlock(pa[j]);
                                }
                                if (m == NULL)
                                        softerr = ENOBUFS;
                                fixspace(npages, i, off, &space);
                                npages = i;
                                break;
                        }

                        m0 = m_get(M_WAITOK, MT_DATA);
                        m0->m_ext.ext_buf = (char *)sf_buf_kva(sf);
                        m0->m_ext.ext_size = PAGE_SIZE;
                        m0->m_ext.ext_arg1 = sf;
                        m0->m_ext.ext_arg2 = sfs;
                        /*
                         * SF_NOCACHE sets the page as being freed upon send.
                         * However, we ignore it for the last page in 'space',
                         * if the page is truncated, and we got more data to
                         * send (rem > space), or if we have readahead
                         * configured (rhpages > 0).
                         */
                        if ((flags & SF_NOCACHE) == 0 ||
                            (i == npages - 1 &&
                            ((off + space) & PAGE_MASK) &&
                            (rem > space || rhpages > 0)))
                                m0->m_ext.ext_type = EXT_SFBUF;
                        else
                                m0->m_ext.ext_type = EXT_SFBUF_NOCACHE;
                        m0->m_ext.ext_flags = EXT_FLAG_EMBREF;
                        m0->m_ext.ext_count = 1;
                        m0->m_flags |= (M_EXT | M_RDONLY);
                        if (nios)
                                m0->m_flags |= M_NOTREADY;
                        m0->m_data = (char *)sf_buf_kva(sf) +
                            (vmoff(i, off) & PAGE_MASK);
                        m0->m_len = xfsize(i, npages, off, space);

                        if (i == 0)
                                sfio->m = m0;

                        /* Append to mbuf chain. */
                        if (mtail != NULL)
                                mtail->m_next = m0;
                        else
                                m = m0;
                        mtail = m0;

                        if (sfs != NULL) {
                                mtx_lock(&sfs->mtx);
                                sfs->count++;
                                mtx_unlock(&sfs->mtx);
                        }
                }

                if (vp != NULL)
                        VOP_UNLOCK(vp, 0);

                /* Keep track of bytes processed. */
                off += space;
                rem -= space;

                /* Prepend header, if any. */
                if (hdrlen) {
prepend_header:
                        mhtail->m_next = m;
                        m = mh;
                        mh = NULL;
                }

                if (m == NULL) {
                        KASSERT(softerr, ("%s: m NULL, no error", __func__));
                        error = softerr;
                        free(sfio, M_TEMP);
                        goto done;
                }

                /* Add the buffer chain to the socket buffer. */
                KASSERT(m_length(m, NULL) == space + hdrlen,
                    ("%s: mlen %u space %d hdrlen %d",
                    __func__, m_length(m, NULL), space, hdrlen));

                CURVNET_SET(so->so_vnet);
                if (nios == 0) {
                        /*
                         * If sendfile_swapin() didn't initiate any I/Os,
                         * which happens if all data is cached in VM, then
                         * we can send data right now without the
                         * PRUS_NOTREADY flag.
                         */
                        free(sfio, M_TEMP);
                        error = (*so->so_proto->pr_usrreqs->pru_send)
                            (so, 0, m, NULL, NULL, td);
                } else {
                        sfio->sock_fp = sock_fp;
                        sfio->npages = npages;
                        fhold(sock_fp);
                        error = (*so->so_proto->pr_usrreqs->pru_send)
                            (so, PRUS_NOTREADY, m, NULL, NULL, td);
                        sendfile_iodone(sfio, NULL, 0, 0);
                }
                CURVNET_RESTORE();

                m = NULL;       /* pru_send always consumes */
                if (error)
                        goto done;
                sbytes += space + hdrlen;
                if (hdrlen)
                        hdrlen = 0;
                if (softerr) {
                        error = softerr;
                        goto done;
                }
        }

        /*
         * Send trailers. Wimp out and use writev(2).
         */
        if (trl_uio != NULL) {
                sbunlock(&so->so_snd);
                error = kern_writev(td, sockfd, trl_uio);
                if (error == 0)
                        sbytes += td->td_retval[0];
                goto out;
        }

done:
        sbunlock(&so->so_snd);
out:
        /*
         * If there was no error we have to clear td->td_retval[0]
         * because it may have been set by writev.
         */
        if (error == 0) {
                td->td_retval[0] = 0;
        }
        if (sent != NULL) {
                (*sent) = sbytes;
        }
        if (obj != NULL)
                vm_object_deallocate(obj);
        if (so)
                fdrop(sock_fp, td);
        if (m)
                m_freem(m);
        if (mh)
                m_freem(mh);

        if (sfs != NULL) {
                mtx_lock(&sfs->mtx);
                if (sfs->count != 0)
                        cv_wait(&sfs->cv, &sfs->mtx);
                KASSERT(sfs->count == 0, ("sendfile sync still busy"));
                cv_destroy(&sfs->cv);
                mtx_destroy(&sfs->mtx);
                free(sfs, M_TEMP);
        }

        if (error == ERESTART)
                error = EINTR;

        return (error);
}

static int
sendfile(struct thread *td, struct sendfile_args *uap, int compat)
{
        struct sf_hdtr hdtr;
        struct uio *hdr_uio, *trl_uio;
        struct file *fp;
        cap_rights_t rights;
        off_t sbytes;
        int error;

        /*
         * File offset must be positive.  If it goes beyond EOF
         * we send only the header/trailer and no payload data.
         */
        if (uap->offset < 0)
                return (EINVAL);

        sbytes = 0;
        hdr_uio = trl_uio = NULL;

        if (uap->hdtr != NULL) {
                error = copyin(uap->hdtr, &hdtr, sizeof(hdtr));
                if (error != 0)
                        goto out;
                if (hdtr.headers != NULL) {
                        error = copyinuio(hdtr.headers, hdtr.hdr_cnt,
                            &hdr_uio);
                        if (error != 0)
                                goto out;
#ifdef COMPAT_FREEBSD4
                        /*
                         * In FreeBSD < 5.0 the nbytes to send also included
                         * the header.  If compat is specified subtract the
                         * header size from nbytes.
                         */
                        if (compat) {
                                if (uap->nbytes > hdr_uio->uio_resid)
                                        uap->nbytes -= hdr_uio->uio_resid;
                                else
                                        uap->nbytes = 0;
                        }
#endif
                }
                if (hdtr.trailers != NULL) {
                        error = copyinuio(hdtr.trailers, hdtr.trl_cnt,
                            &trl_uio);
                        if (error != 0)
                                goto out;
                }
        }

        AUDIT_ARG_FD(uap->fd);

        /*
         * sendfile(2) can start at any offset within a file so we require
         * CAP_READ+CAP_SEEK = CAP_PREAD.
         */
        if ((error = fget_read(td, uap->fd,
            cap_rights_init(&rights, CAP_PREAD), &fp)) != 0) {
                goto out;
        }

        error = fo_sendfile(fp, uap->s, hdr_uio, trl_uio, uap->offset,
            uap->nbytes, &sbytes, uap->flags, td);
        fdrop(fp, td);

        if (uap->sbytes != NULL)
                copyout(&sbytes, uap->sbytes, sizeof(off_t));

out:
        free(hdr_uio, M_IOV);
        free(trl_uio, M_IOV);
        return (error);
}

/*
 * sendfile(2)
 * 
 * int sendfile(int fd, int s, off_t offset, size_t nbytes,
 *       struct sf_hdtr *hdtr, off_t *sbytes, int flags)
 * 
 * Send a file specified by 'fd' and starting at 'offset' to a socket
 * specified by 's'. Send only 'nbytes' of the file or until EOF if nbytes ==
 * 0.  Optionally add a header and/or trailer to the socket output.  If
 * specified, write the total number of bytes sent into *sbytes.
 */
int
sys_sendfile(struct thread *td, struct sendfile_args *uap)
{
 
        return (sendfile(td, uap, 0));
}

#ifdef COMPAT_FREEBSD4
int
freebsd4_sendfile(struct thread *td, struct freebsd4_sendfile_args *uap)
{
        struct sendfile_args args;

        args.fd = uap->fd;
        args.s = uap->s;
        args.offset = uap->offset;
        args.nbytes = uap->nbytes;
        args.hdtr = uap->hdtr;
        args.sbytes = uap->sbytes;
        args.flags = uap->flags;

        return (sendfile(td, &args, 1));
}
#endif /* COMPAT_FREEBSD4 */