2 * Copyright (c) 1989, 1993
3 * The Regents of the University of California.
4 * Copyright (c) 2005 Robert N. M. Watson
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 4. Neither the name of the University nor the names of its contributors
16 * may be used to endorse or promote products derived from this software
17 * without specific prior written permission.
19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * @(#)kern_ktrace.c 8.2 (Berkeley) 9/23/93
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
37 #include "opt_ktrace.h"
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/fcntl.h>
43 #include <sys/kernel.h>
44 #include <sys/kthread.h>
46 #include <sys/mutex.h>
48 #include <sys/malloc.h>
49 #include <sys/mount.h>
50 #include <sys/namei.h>
52 #include <sys/unistd.h>
53 #include <sys/vnode.h>
54 #include <sys/ktrace.h>
56 #include <sys/sysctl.h>
57 #include <sys/syslog.h>
58 #include <sys/sysproto.h>
61 * The ktrace facility allows the tracing of certain key events in user space
62 * processes, such as system calls, signal delivery, context switches, and
63 * user generated events using utrace(2). It works by streaming event
64 * records and data to a vnode associated with the process using the
65 * ktrace(2) system call. In general, records can be written directly from
66 * the context that generates the event. One important exception to this is
67 * during a context switch, where sleeping is not permitted. To handle this
68 * case, trace events are generated using in-kernel ktr_request records, and
69 * then delivered to disk at a convenient moment -- either immediately, the
70 * next traceable event, at system call return, or at process exit.
72 * When dealing with multiple threads or processes writing to the same event
73 * log, ordering guarantees are weak: specifically, if an event has multiple
74 * records (i.e., system call enter and return), they may be interlaced with
75 * records from another event. Process and thread ID information is provided
76 * in the record, and user applications can de-interlace events if required.
79 static MALLOC_DEFINE(M_KTRACE, "KTRACE", "KTRACE");
83 #ifndef KTRACE_REQUEST_POOL
84 #define KTRACE_REQUEST_POOL 100
88 struct ktr_header ktr_header;
91 struct ktr_syscall ktr_syscall;
92 struct ktr_sysret ktr_sysret;
93 struct ktr_genio ktr_genio;
94 struct ktr_psig ktr_psig;
95 struct ktr_csw ktr_csw;
97 STAILQ_ENTRY(ktr_request) ktr_list;
100 static int data_lengths[] = {
102 offsetof(struct ktr_syscall, ktr_args), /* KTR_SYSCALL */
103 sizeof(struct ktr_sysret), /* KTR_SYSRET */
105 sizeof(struct ktr_genio), /* KTR_GENIO */
106 sizeof(struct ktr_psig), /* KTR_PSIG */
107 sizeof(struct ktr_csw), /* KTR_CSW */
111 static STAILQ_HEAD(, ktr_request) ktr_free;
113 static SYSCTL_NODE(_kern, OID_AUTO, ktrace, CTLFLAG_RD, 0, "KTRACE options");
115 static u_int ktr_requestpool = KTRACE_REQUEST_POOL;
116 TUNABLE_INT("kern.ktrace.request_pool", &ktr_requestpool);
118 static u_int ktr_geniosize = PAGE_SIZE;
119 TUNABLE_INT("kern.ktrace.genio_size", &ktr_geniosize);
120 SYSCTL_UINT(_kern_ktrace, OID_AUTO, genio_size, CTLFLAG_RW, &ktr_geniosize,
121 0, "Maximum size of genio event payload");
123 static int print_message = 1;
124 struct mtx ktrace_mtx;
125 static struct cv ktrace_cv;
126 static struct sx ktrace_sx;
128 static void ktrace_init(void *dummy);
129 static int sysctl_kern_ktrace_request_pool(SYSCTL_HANDLER_ARGS);
130 static u_int ktrace_resize_pool(u_int newsize);
131 static struct ktr_request *ktr_getrequest(int type);
132 static void ktr_submitrequest(struct thread *td, struct ktr_request *req);
133 static void ktr_freerequest(struct ktr_request *req);
134 static void ktr_writerequest(struct thread *td, struct ktr_request *req);
135 static int ktrcanset(struct thread *,struct proc *);
136 static int ktrsetchildren(struct thread *,struct proc *,int,int,struct vnode *);
137 static int ktrops(struct thread *,struct proc *,int,int,struct vnode *);
140 * ktrace itself generates events, such as context switches, which we do not
141 * wish to trace. Maintain a flag, TDP_INKTRACE, on each thread to determine
142 * whether or not it is in a region where tracing of events should be
146 ktrace_enter(struct thread *td)
149 KASSERT(!(td->td_pflags & TDP_INKTRACE), ("ktrace_enter: flag set"));
150 td->td_pflags |= TDP_INKTRACE;
154 ktrace_exit(struct thread *td)
157 KASSERT(td->td_pflags & TDP_INKTRACE, ("ktrace_exit: flag not set"));
158 td->td_pflags &= ~TDP_INKTRACE;
162 ktrace_assert(struct thread *td)
165 KASSERT(td->td_pflags & TDP_INKTRACE, ("ktrace_assert: flag not set"));
169 ktrace_init(void *dummy)
171 struct ktr_request *req;
174 mtx_init(&ktrace_mtx, "ktrace", NULL, MTX_DEF | MTX_QUIET);
175 sx_init(&ktrace_sx, "ktrace_sx");
176 cv_init(&ktrace_cv, "ktrace");
177 STAILQ_INIT(&ktr_free);
178 for (i = 0; i < ktr_requestpool; i++) {
179 req = malloc(sizeof(struct ktr_request), M_KTRACE, M_WAITOK);
180 STAILQ_INSERT_HEAD(&ktr_free, req, ktr_list);
183 SYSINIT(ktrace_init, SI_SUB_KTRACE, SI_ORDER_ANY, ktrace_init, NULL);
186 sysctl_kern_ktrace_request_pool(SYSCTL_HANDLER_ARGS)
189 u_int newsize, oldsize, wantsize;
192 /* Handle easy read-only case first to avoid warnings from GCC. */
194 mtx_lock(&ktrace_mtx);
195 oldsize = ktr_requestpool;
196 mtx_unlock(&ktrace_mtx);
197 return (SYSCTL_OUT(req, &oldsize, sizeof(u_int)));
200 error = SYSCTL_IN(req, &wantsize, sizeof(u_int));
205 mtx_lock(&ktrace_mtx);
206 oldsize = ktr_requestpool;
207 newsize = ktrace_resize_pool(wantsize);
208 mtx_unlock(&ktrace_mtx);
210 error = SYSCTL_OUT(req, &oldsize, sizeof(u_int));
213 if (wantsize > oldsize && newsize < wantsize)
217 SYSCTL_PROC(_kern_ktrace, OID_AUTO, request_pool, CTLTYPE_UINT|CTLFLAG_RW,
218 &ktr_requestpool, 0, sysctl_kern_ktrace_request_pool, "IU", "");
221 ktrace_resize_pool(u_int newsize)
223 struct ktr_request *req;
226 mtx_assert(&ktrace_mtx, MA_OWNED);
228 bound = newsize - ktr_requestpool;
230 return (ktr_requestpool);
232 /* Shrink pool down to newsize if possible. */
233 while (bound++ < 0) {
234 req = STAILQ_FIRST(&ktr_free);
236 return (ktr_requestpool);
237 STAILQ_REMOVE_HEAD(&ktr_free, ktr_list);
239 mtx_unlock(&ktrace_mtx);
241 mtx_lock(&ktrace_mtx);
244 /* Grow pool up to newsize. */
245 while (bound-- > 0) {
246 mtx_unlock(&ktrace_mtx);
247 req = malloc(sizeof(struct ktr_request), M_KTRACE,
249 mtx_lock(&ktrace_mtx);
250 STAILQ_INSERT_HEAD(&ktr_free, req, ktr_list);
253 return (ktr_requestpool);
256 static struct ktr_request *
257 ktr_getrequest(int type)
259 struct ktr_request *req;
260 struct thread *td = curthread;
261 struct proc *p = td->td_proc;
264 ktrace_enter(td); /* XXX: In caller instead? */
265 mtx_lock(&ktrace_mtx);
266 if (!KTRCHECK(td, type)) {
267 mtx_unlock(&ktrace_mtx);
271 req = STAILQ_FIRST(&ktr_free);
273 STAILQ_REMOVE_HEAD(&ktr_free, ktr_list);
274 req->ktr_header.ktr_type = type;
275 if (p->p_traceflag & KTRFAC_DROP) {
276 req->ktr_header.ktr_type |= KTR_DROP;
277 p->p_traceflag &= ~KTRFAC_DROP;
279 mtx_unlock(&ktrace_mtx);
280 microtime(&req->ktr_header.ktr_time);
281 req->ktr_header.ktr_pid = p->p_pid;
282 req->ktr_header.ktr_tid = td->td_tid;
283 bcopy(p->p_comm, req->ktr_header.ktr_comm, MAXCOMLEN + 1);
284 req->ktr_buffer = NULL;
285 req->ktr_header.ktr_len = 0;
287 p->p_traceflag |= KTRFAC_DROP;
290 mtx_unlock(&ktrace_mtx);
292 printf("Out of ktrace request objects.\n");
299 * Some trace generation environments don't permit direct access to VFS,
300 * such as during a context switch where sleeping is not allowed. Under these
301 * circumstances, queue a request to the thread to be written asynchronously
305 ktr_enqueuerequest(struct thread *td, struct ktr_request *req)
308 mtx_lock(&ktrace_mtx);
309 STAILQ_INSERT_TAIL(&td->td_proc->p_ktr, req, ktr_list);
310 mtx_unlock(&ktrace_mtx);
315 * Drain any pending ktrace records from the per-thread queue to disk. This
316 * is used both internally before committing other records, and also on
317 * system call return. We drain all the ones we can find at the time when
318 * drain is requested, but don't keep draining after that as those events
319 * may me approximately "after" the current event.
322 ktr_drain(struct thread *td)
324 struct ktr_request *queued_req;
325 STAILQ_HEAD(, ktr_request) local_queue;
328 sx_assert(&ktrace_sx, SX_XLOCKED);
330 STAILQ_INIT(&local_queue); /* XXXRW: needed? */
332 if (!STAILQ_EMPTY(&td->td_proc->p_ktr)) {
333 mtx_lock(&ktrace_mtx);
334 STAILQ_CONCAT(&local_queue, &td->td_proc->p_ktr);
335 mtx_unlock(&ktrace_mtx);
337 while ((queued_req = STAILQ_FIRST(&local_queue))) {
338 STAILQ_REMOVE_HEAD(&local_queue, ktr_list);
339 ktr_writerequest(td, queued_req);
340 ktr_freerequest(queued_req);
346 * Submit a trace record for immediate commit to disk -- to be used only
347 * where entering VFS is OK. First drain any pending records that may have
348 * been cached in the thread.
351 ktr_submitrequest(struct thread *td, struct ktr_request *req)
356 sx_xlock(&ktrace_sx);
358 ktr_writerequest(td, req);
359 ktr_freerequest(req);
360 sx_xunlock(&ktrace_sx);
366 ktr_freerequest(struct ktr_request *req)
369 if (req->ktr_buffer != NULL)
370 free(req->ktr_buffer, M_KTRACE);
371 mtx_lock(&ktrace_mtx);
372 STAILQ_INSERT_HEAD(&ktr_free, req, ktr_list);
373 mtx_unlock(&ktrace_mtx);
380 ktrsyscall(code, narg, args)
384 struct ktr_request *req;
385 struct ktr_syscall *ktp;
389 buflen = sizeof(register_t) * narg;
391 buf = malloc(buflen, M_KTRACE, M_WAITOK);
392 bcopy(args, buf, buflen);
394 req = ktr_getrequest(KTR_SYSCALL);
400 ktp = &req->ktr_data.ktr_syscall;
401 ktp->ktr_code = code;
402 ktp->ktr_narg = narg;
404 req->ktr_header.ktr_len = buflen;
405 req->ktr_buffer = buf;
407 ktr_submitrequest(curthread, req);
414 ktrsysret(code, error, retval)
418 struct ktr_request *req;
419 struct ktr_sysret *ktp;
421 req = ktr_getrequest(KTR_SYSRET);
424 ktp = &req->ktr_data.ktr_sysret;
425 ktp->ktr_code = code;
426 ktp->ktr_error = error;
427 ktp->ktr_retval = retval; /* what about val2 ? */
428 ktr_submitrequest(curthread, req);
432 * When a process exits, drain per-process asynchronous trace records.
435 ktrprocexit(struct thread *td)
439 sx_xlock(&ktrace_sx);
441 sx_xunlock(&ktrace_sx);
446 * When a thread returns, drain any asynchronous records generated by the
450 ktruserret(struct thread *td)
454 sx_xlock(&ktrace_sx);
456 sx_xunlock(&ktrace_sx);
464 struct ktr_request *req;
468 namelen = strlen(path);
470 buf = malloc(namelen, M_KTRACE, M_WAITOK);
471 bcopy(path, buf, namelen);
473 req = ktr_getrequest(KTR_NAMEI);
480 req->ktr_header.ktr_len = namelen;
481 req->ktr_buffer = buf;
483 ktr_submitrequest(curthread, req);
487 * Since the uio may not stay valid, we can not hand off this request to
488 * the thread and need to process it synchronously. However, we wish to
489 * keep the relative order of records in a trace file correct, so we
490 * do put this request on the queue (if it isn't empty) and then block.
491 * The ktrace thread waks us back up when it is time for this event to
492 * be posted and blocks until we have completed writing out the event
493 * and woken it back up.
496 ktrgenio(fd, rw, uio, error)
502 struct ktr_request *req;
503 struct ktr_genio *ktg;
512 uio->uio_rw = UIO_WRITE;
513 datalen = imin(uio->uio_resid, ktr_geniosize);
514 buf = malloc(datalen, M_KTRACE, M_WAITOK);
515 error = uiomove(buf, datalen, uio);
521 req = ktr_getrequest(KTR_GENIO);
526 ktg = &req->ktr_data.ktr_genio;
529 req->ktr_header.ktr_len = datalen;
530 req->ktr_buffer = buf;
531 ktr_submitrequest(curthread, req);
535 ktrpsig(sig, action, mask, code)
541 struct ktr_request *req;
544 req = ktr_getrequest(KTR_PSIG);
547 kp = &req->ktr_data.ktr_psig;
548 kp->signo = (char)sig;
552 ktr_enqueuerequest(curthread, req);
559 struct ktr_request *req;
562 req = ktr_getrequest(KTR_CSW);
565 kc = &req->ktr_data.ktr_csw;
568 ktr_enqueuerequest(curthread, req);
572 /* Interface and common routines */
579 #ifndef _SYS_SYSPROTO_H_
591 register struct ktrace_args *uap;
594 register struct vnode *vp = NULL;
595 register struct proc *p;
597 int facs = uap->facs & ~KTRFAC_ROOT;
598 int ops = KTROP(uap->ops);
599 int descend = uap->ops & KTRFLAG_DESCEND;
601 int flags, error = 0;
606 * Need something to (un)trace.
608 if (ops != KTROP_CLEARFILE && facs == 0)
612 if (ops != KTROP_CLEAR) {
614 * an operation which requires a file argument.
616 NDINIT(&nd, LOOKUP, NOFOLLOW, UIO_USERSPACE, uap->fname, td);
617 flags = FREAD | FWRITE | O_NOFOLLOW;
619 error = vn_open(&nd, &flags, 0, -1);
625 NDFREE(&nd, NDF_ONLY_PNBUF);
627 VOP_UNLOCK(vp, 0, td);
628 if (vp->v_type != VREG) {
629 (void) vn_close(vp, FREAD|FWRITE, td->td_ucred, td);
637 * Clear all uses of the tracefile.
639 if (ops == KTROP_CLEARFILE) {
640 sx_slock(&allproc_lock);
641 LIST_FOREACH(p, &allproc, p_list) {
643 if (p->p_tracevp == vp) {
644 if (ktrcanset(td, p)) {
645 mtx_lock(&ktrace_mtx);
646 cred = p->p_tracecred;
647 p->p_tracecred = NULL;
650 mtx_unlock(&ktrace_mtx);
653 (void) vn_close(vp, FREAD|FWRITE,
664 sx_sunlock(&allproc_lock);
670 sx_slock(&proctree_lock);
675 pg = pgfind(-uap->pid);
677 sx_sunlock(&proctree_lock);
682 * ktrops() may call vrele(). Lock pg_members
683 * by the proctree_lock rather than pg_mtx.
687 LIST_FOREACH(p, &pg->pg_members, p_pglist) {
689 if (p_cansee(td, p) != 0) {
696 ret |= ktrsetchildren(td, p, ops, facs, vp);
698 ret |= ktrops(td, p, ops, facs, vp);
701 sx_sunlock(&proctree_lock);
711 sx_sunlock(&proctree_lock);
715 error = p_cansee(td, p);
717 * The slock of the proctree lock will keep this process
718 * from going away, so unlocking the proc here is ok.
722 sx_sunlock(&proctree_lock);
726 ret |= ktrsetchildren(td, p, ops, facs, vp);
728 ret |= ktrops(td, p, ops, facs, vp);
730 sx_sunlock(&proctree_lock);
736 (void) vn_close(vp, FWRITE, td->td_ucred, td);
755 register struct utrace_args *uap;
759 struct ktr_request *req;
763 if (!KTRPOINT(td, KTR_USER))
765 if (uap->len > KTR_USER_MAXLEN)
767 cp = malloc(uap->len, M_KTRACE, M_WAITOK);
768 error = copyin(uap->addr, cp, uap->len);
773 req = ktr_getrequest(KTR_USER);
778 req->ktr_buffer = cp;
779 req->ktr_header.ktr_len = uap->len;
780 ktr_submitrequest(td, req);
789 ktrops(td, p, ops, facs, vp)
795 struct vnode *tracevp = NULL;
796 struct ucred *tracecred = NULL;
799 if (!ktrcanset(td, p)) {
803 mtx_lock(&ktrace_mtx);
804 if (ops == KTROP_SET) {
805 if (p->p_tracevp != vp) {
807 * if trace file already in use, relinquish below
809 tracevp = p->p_tracevp;
813 if (p->p_tracecred != td->td_ucred) {
814 tracecred = p->p_tracecred;
815 p->p_tracecred = crhold(td->td_ucred);
817 p->p_traceflag |= facs;
818 if (td->td_ucred->cr_uid == 0)
819 p->p_traceflag |= KTRFAC_ROOT;
822 if (((p->p_traceflag &= ~facs) & KTRFAC_MASK) == 0) {
823 /* no more tracing */
825 tracevp = p->p_tracevp;
827 tracecred = p->p_tracecred;
828 p->p_tracecred = NULL;
831 mtx_unlock(&ktrace_mtx);
833 if (tracevp != NULL) {
836 vfslocked = VFS_LOCK_GIANT(tracevp->v_mount);
838 VFS_UNLOCK_GIANT(vfslocked);
840 if (tracecred != NULL)
847 ktrsetchildren(td, top, ops, facs, vp)
853 register struct proc *p;
854 register int ret = 0;
857 sx_assert(&proctree_lock, SX_LOCKED);
859 ret |= ktrops(td, p, ops, facs, vp);
861 * If this process has children, descend to them next,
862 * otherwise do any siblings, and if done with this level,
863 * follow back up the tree (but not past top).
865 if (!LIST_EMPTY(&p->p_children))
866 p = LIST_FIRST(&p->p_children);
870 if (LIST_NEXT(p, p_sibling)) {
871 p = LIST_NEXT(p, p_sibling);
881 ktr_writerequest(struct thread *td, struct ktr_request *req)
883 struct ktr_header *kth;
888 struct iovec aiov[3];
890 int datalen, buflen, vrele_count;
894 * We hold the vnode and credential for use in I/O in case ktrace is
895 * disabled on the process as we write out the request.
897 * XXXRW: This is not ideal: we could end up performing a write after
898 * the vnode has been closed.
900 mtx_lock(&ktrace_mtx);
901 vp = td->td_proc->p_tracevp;
904 cred = td->td_proc->p_tracecred;
907 mtx_unlock(&ktrace_mtx);
910 * If vp is NULL, the vp has been cleared out from under this
911 * request, so just drop it. Make sure the credential and vnode are
912 * in sync: we should have both or neither.
915 KASSERT(cred == NULL, ("ktr_writerequest: cred != NULL"));
918 KASSERT(cred != NULL, ("ktr_writerequest: cred == NULL"));
920 kth = &req->ktr_header;
921 datalen = data_lengths[(u_short)kth->ktr_type & ~KTR_DROP];
922 buflen = kth->ktr_len;
923 auio.uio_iov = &aiov[0];
925 auio.uio_segflg = UIO_SYSSPACE;
926 auio.uio_rw = UIO_WRITE;
927 aiov[0].iov_base = (caddr_t)kth;
928 aiov[0].iov_len = sizeof(struct ktr_header);
929 auio.uio_resid = sizeof(struct ktr_header);
933 aiov[1].iov_base = (caddr_t)&req->ktr_data;
934 aiov[1].iov_len = datalen;
935 auio.uio_resid += datalen;
937 kth->ktr_len += datalen;
940 KASSERT(req->ktr_buffer != NULL, ("ktrace: nothing to write"));
941 aiov[auio.uio_iovcnt].iov_base = req->ktr_buffer;
942 aiov[auio.uio_iovcnt].iov_len = buflen;
943 auio.uio_resid += buflen;
948 vn_start_write(vp, &mp, V_WAIT);
949 vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, td);
950 (void)VOP_LEASE(vp, td, cred, LEASE_WRITE);
952 error = mac_check_vnode_write(cred, NOCRED, vp);
955 error = VOP_WRITE(vp, &auio, IO_UNIT | IO_APPEND, cred);
956 VOP_UNLOCK(vp, 0, td);
957 vn_finished_write(mp);
963 * If error encountered, give up tracing on this vnode. We defer
964 * all the vrele()'s on the vnode until after we are finished walking
965 * the various lists to avoid needlessly holding locks.
967 log(LOG_NOTICE, "ktrace write failed, errno %d, tracing stopped\n",
971 * First, clear this vnode from being used by any processes in the
973 * XXX - If one process gets an EPERM writing to the vnode, should
974 * we really do this? Other processes might have suitable
975 * credentials for the operation.
978 sx_slock(&allproc_lock);
979 LIST_FOREACH(p, &allproc, p_list) {
981 if (p->p_tracevp == vp) {
982 mtx_lock(&ktrace_mtx);
985 cred = p->p_tracecred;
986 p->p_tracecred = NULL;
987 mtx_unlock(&ktrace_mtx);
996 sx_sunlock(&allproc_lock);
999 * We can't clear any pending requests in threads that have cached
1000 * them but not yet committed them, as those are per-thread. The
1001 * thread will have to clear it itself on system call return.
1004 while (vrele_count-- > 0)
1010 * Return true if caller has permission to set the ktracing state
1011 * of target. Essentially, the target can't possess any
1012 * more permissions than the caller. KTRFAC_ROOT signifies that
1013 * root previously set the tracing status on the target process, and
1014 * so, only root may further change it.
1017 ktrcanset(td, targetp)
1019 struct proc *targetp;
1022 PROC_LOCK_ASSERT(targetp, MA_OWNED);
1023 if (targetp->p_traceflag & KTRFAC_ROOT &&
1024 suser_cred(td->td_ucred, SUSER_ALLOWJAIL))
1027 if (p_candebug(td, targetp) != 0)