xref: /freebsd/sys/fs/fuse/fuse_vfsops.c (revision 105fd928b0b5b35ab529e5f6914788dc49582901)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
3  *
4  * Copyright (c) 2007-2009 Google Inc. and Amit Singh
5  * All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions are
9  * met:
10  *
11  * * Redistributions of source code must retain the above copyright
12  *   notice, this list of conditions and the following disclaimer.
13  * * Redistributions in binary form must reproduce the above
14  *   copyright notice, this list of conditions and the following disclaimer
15  *   in the documentation and/or other materials provided with the
16  *   distribution.
17  * * Neither the name of Google Inc. nor the names of its
18  *   contributors may be used to endorse or promote products derived from
19  *   this software without specific prior written permission.
20  *
21  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
23  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
24  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
25  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
26  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
27  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
28  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
29  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
30  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
31  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
32  *
33  * Copyright (C) 2005 Csaba Henk.
34  * All rights reserved.
35  *
36  * Copyright (c) 2019 The FreeBSD Foundation
37  *
38  * Portions of this software were developed by BFF Storage Systems, LLC under
39  * sponsorship from the FreeBSD Foundation.
40  *
41  * Redistribution and use in source and binary forms, with or without
42  * modification, are permitted provided that the following conditions
43  * are met:
44  * 1. Redistributions of source code must retain the above copyright
45  *    notice, this list of conditions and the following disclaimer.
46  * 2. Redistributions in binary form must reproduce the above copyright
47  *    notice, this list of conditions and the following disclaimer in the
48  *    documentation and/or other materials provided with the distribution.
49  *
50  * THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
51  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
52  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
53  * ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
54  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
55  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
56  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
57  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
58  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
59  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
60  * SUCH DAMAGE.
61  */
62 
63 #include <sys/cdefs.h>
64 __FBSDID("$FreeBSD$");
65 
66 #include <sys/param.h>
67 #include <sys/buf.h>
68 #include <sys/module.h>
69 #include <sys/systm.h>
70 #include <sys/errno.h>
71 #include <sys/kernel.h>
72 #include <sys/capsicum.h>
73 #include <sys/conf.h>
74 #include <sys/filedesc.h>
75 #include <sys/uio.h>
76 #include <sys/malloc.h>
77 #include <sys/queue.h>
78 #include <sys/lock.h>
79 #include <sys/sx.h>
80 #include <sys/mutex.h>
81 #include <sys/proc.h>
82 #include <sys/vnode.h>
83 #include <sys/namei.h>
84 #include <sys/mount.h>
85 #include <sys/sysctl.h>
86 #include <sys/fcntl.h>
87 
88 #include "fuse.h"
89 #include "fuse_node.h"
90 #include "fuse_ipc.h"
91 #include "fuse_internal.h"
92 
93 #include <sys/priv.h>
94 #include <security/mac/mac_framework.h>
95 
96 SDT_PROVIDER_DECLARE(fusefs);
97 /*
98  * Fuse trace probe:
99  * arg0: verbosity.  Higher numbers give more verbose messages
100  * arg1: Textual message
101  */
102 SDT_PROBE_DEFINE2(fusefs, , vfsops, trace, "int", "char*");
103 
104 /* This will do for privilege types for now */
105 #ifndef PRIV_VFS_FUSE_ALLOWOTHER
106 #define PRIV_VFS_FUSE_ALLOWOTHER PRIV_VFS_MOUNT_NONUSER
107 #endif
108 #ifndef PRIV_VFS_FUSE_MOUNT_NONUSER
109 #define PRIV_VFS_FUSE_MOUNT_NONUSER PRIV_VFS_MOUNT_NONUSER
110 #endif
111 #ifndef PRIV_VFS_FUSE_SYNC_UNMOUNT
112 #define PRIV_VFS_FUSE_SYNC_UNMOUNT PRIV_VFS_MOUNT_NONUSER
113 #endif
114 
115 static vfs_fhtovp_t fuse_vfsop_fhtovp;
116 static vfs_mount_t fuse_vfsop_mount;
117 static vfs_unmount_t fuse_vfsop_unmount;
118 static vfs_root_t fuse_vfsop_root;
119 static vfs_statfs_t fuse_vfsop_statfs;
120 static vfs_vget_t fuse_vfsop_vget;
121 
122 struct vfsops fuse_vfsops = {
123 	.vfs_fhtovp = fuse_vfsop_fhtovp,
124 	.vfs_mount = fuse_vfsop_mount,
125 	.vfs_unmount = fuse_vfsop_unmount,
126 	.vfs_root = fuse_vfsop_root,
127 	.vfs_statfs = fuse_vfsop_statfs,
128 	.vfs_vget = fuse_vfsop_vget,
129 };
130 
131 static int fuse_enforce_dev_perms = 0;
132 
133 SYSCTL_INT(_vfs_fusefs, OID_AUTO, enforce_dev_perms, CTLFLAG_RW,
134     &fuse_enforce_dev_perms, 0,
135     "enforce fuse device permissions for secondary mounts");
136 
137 MALLOC_DEFINE(M_FUSEVFS, "fuse_filesystem", "buffer for fuse vfs layer");
138 
139 static int
140 fuse_getdevice(const char *fspec, struct thread *td, struct cdev **fdevp)
141 {
142 	struct nameidata nd, *ndp = &nd;
143 	struct vnode *devvp;
144 	struct cdev *fdev;
145 	int err;
146 
147 	/*
148 	 * Not an update, or updating the name: look up the name
149 	 * and verify that it refers to a sensible disk device.
150 	 */
151 
152 	NDINIT(ndp, LOOKUP, FOLLOW, UIO_SYSSPACE, fspec, td);
153 	if ((err = namei(ndp)) != 0)
154 		return err;
155 	NDFREE(ndp, NDF_ONLY_PNBUF);
156 	devvp = ndp->ni_vp;
157 
158 	if (devvp->v_type != VCHR) {
159 		vrele(devvp);
160 		return ENXIO;
161 	}
162 	fdev = devvp->v_rdev;
163 	dev_ref(fdev);
164 
165 	if (fuse_enforce_dev_perms) {
166 		/*
167 	         * Check if mounter can open the fuse device.
168 	         *
169 	         * This has significance only if we are doing a secondary mount
170 	         * which doesn't involve actually opening fuse devices, but we
171 	         * still want to enforce the permissions of the device (in
172 	         * order to keep control over the circle of fuse users).
173 	         *
174 	         * (In case of primary mounts, we are either the superuser so
175 	         * we can do anything anyway, or we can mount only if the
176 	         * device is already opened by us, ie. we are permitted to open
177 	         * the device.)
178 	         */
179 #if 0
180 #ifdef MAC
181 		err = mac_check_vnode_open(td->td_ucred, devvp, VREAD | VWRITE);
182 		if (!err)
183 #endif
184 #endif /* 0 */
185 			err = VOP_ACCESS(devvp, VREAD | VWRITE, td->td_ucred, td);
186 		if (err) {
187 			vrele(devvp);
188 			dev_rel(fdev);
189 			return err;
190 		}
191 	}
192 	/*
193 	 * according to coda code, no extra lock is needed --
194 	 * although in sys/vnode.h this field is marked "v"
195 	 */
196 	vrele(devvp);
197 
198 	if (!fdev->si_devsw ||
199 	    strcmp("fuse", fdev->si_devsw->d_name)) {
200 		dev_rel(fdev);
201 		return ENXIO;
202 	}
203 	*fdevp = fdev;
204 
205 	return 0;
206 }
207 
208 #define FUSE_FLAGOPT(fnam, fval) do {				\
209 	vfs_flagopt(opts, #fnam, &mntopts, fval);		\
210 	vfs_flagopt(opts, "__" #fnam, &__mntopts, fval);	\
211 } while (0)
212 
213 SDT_PROBE_DEFINE1(fusefs, , vfsops, mntopts, "uint64_t");
214 SDT_PROBE_DEFINE4(fusefs, , vfsops, mount_err, "char*", "struct fuse_data*",
215 	"struct mount*", "int");
216 
217 static int
218 fuse_vfs_remount(struct mount *mp, struct thread *td, uint64_t mntopts,
219 	uint32_t max_read, int daemon_timeout)
220 {
221 	int err = 0;
222 	struct fuse_data *data = fuse_get_mpdata(mp);
223 	/* Don't allow these options to be changed */
224 	const static unsigned long long cant_update_opts =
225 		MNT_USER;	/* Mount owner must be the user running the daemon */
226 
227 	FUSE_LOCK();
228 
229 	if ((mp->mnt_flag ^ data->mnt_flag) & cant_update_opts) {
230 		err = EOPNOTSUPP;
231 		SDT_PROBE4(fusefs, , vfsops, mount_err,
232 			"Can't change these mount options during remount",
233 			data, mp, err);
234 		goto out;
235 	}
236 	if (((data->dataflags ^ mntopts) & FSESS_MNTOPTS_MASK) ||
237 	     (data->max_read != max_read) ||
238 	     (data->daemon_timeout != daemon_timeout)) {
239 		// TODO: allow changing options where it makes sense
240 		err = EOPNOTSUPP;
241 		SDT_PROBE4(fusefs, , vfsops, mount_err,
242 			"Can't change fuse mount options during remount",
243 			data, mp, err);
244 		goto out;
245 	}
246 
247 	if (fdata_get_dead(data)) {
248 		err = ENOTCONN;
249 		SDT_PROBE4(fusefs, , vfsops, mount_err,
250 			"device is dead during mount", data, mp, err);
251 		goto out;
252 	}
253 
254 	/* Sanity + permission checks */
255 	if (!data->daemoncred)
256 		panic("fuse daemon found, but identity unknown");
257 	if (mntopts & FSESS_DAEMON_CAN_SPY)
258 		err = priv_check(td, PRIV_VFS_FUSE_ALLOWOTHER);
259 	if (err == 0 && td->td_ucred->cr_uid != data->daemoncred->cr_uid)
260 		/* are we allowed to do the first mount? */
261 		err = priv_check(td, PRIV_VFS_FUSE_MOUNT_NONUSER);
262 
263 out:
264 	FUSE_UNLOCK();
265 	return err;
266 }
267 
268 static int
269 fuse_vfsop_fhtovp(struct mount *mp, struct fid *fhp, int flags,
270 	struct vnode **vpp)
271 {
272 	struct fuse_fid *ffhp = (struct fuse_fid *)fhp;
273 	struct fuse_vnode_data *fvdat;
274 	struct vnode *nvp;
275 	int error;
276 
277 	if (!(fuse_get_mpdata(mp)->dataflags & FSESS_EXPORT_SUPPORT))
278 		return EOPNOTSUPP;
279 
280 	error = VFS_VGET(mp, ffhp->nid, LK_EXCLUSIVE, &nvp);
281 	if (error) {
282 		*vpp = NULLVP;
283 		return (error);
284 	}
285 	fvdat = VTOFUD(nvp);
286 	if (fvdat->generation != ffhp->gen ) {
287 		vput(nvp);
288 		*vpp = NULLVP;
289 		return (ESTALE);
290 	}
291 	*vpp = nvp;
292 	vnode_create_vobject(*vpp, 0, curthread);
293 	return (0);
294 }
295 
296 static int
297 fuse_vfsop_mount(struct mount *mp)
298 {
299 	int err;
300 
301 	uint64_t mntopts, __mntopts;
302 	uint32_t max_read;
303 	int linux_errnos;
304 	int daemon_timeout;
305 	int fd;
306 
307 	struct cdev *fdev;
308 	struct fuse_data *data = NULL;
309 	struct thread *td;
310 	struct file *fp, *fptmp;
311 	char *fspec, *subtype;
312 	struct vfsoptlist *opts;
313 
314 	subtype = NULL;
315 	max_read = ~0;
316 	linux_errnos = 0;
317 	err = 0;
318 	mntopts = 0;
319 	__mntopts = 0;
320 	td = curthread;
321 
322 	/* Get the new options passed to mount */
323 	opts = mp->mnt_optnew;
324 
325 	if (!opts)
326 		return EINVAL;
327 
328 	/* `fspath' contains the mount point (eg. /mnt/fuse/sshfs); REQUIRED */
329 	if (!vfs_getopts(opts, "fspath", &err))
330 		return err;
331 
332 	/*
333 	 * With the help of underscored options the mount program
334 	 * can inform us from the flags it sets by default
335 	 */
336 	FUSE_FLAGOPT(allow_other, FSESS_DAEMON_CAN_SPY);
337 	FUSE_FLAGOPT(push_symlinks_in, FSESS_PUSH_SYMLINKS_IN);
338 	FUSE_FLAGOPT(default_permissions, FSESS_DEFAULT_PERMISSIONS);
339 	FUSE_FLAGOPT(intr, FSESS_INTR);
340 
341 	(void)vfs_scanopt(opts, "max_read=", "%u", &max_read);
342 	(void)vfs_scanopt(opts, "linux_errnos", "%d", &linux_errnos);
343 	if (vfs_scanopt(opts, "timeout=", "%u", &daemon_timeout) == 1) {
344 		if (daemon_timeout < FUSE_MIN_DAEMON_TIMEOUT)
345 			daemon_timeout = FUSE_MIN_DAEMON_TIMEOUT;
346 		else if (daemon_timeout > FUSE_MAX_DAEMON_TIMEOUT)
347 			daemon_timeout = FUSE_MAX_DAEMON_TIMEOUT;
348 	} else {
349 		daemon_timeout = FUSE_DEFAULT_DAEMON_TIMEOUT;
350 	}
351 	subtype = vfs_getopts(opts, "subtype=", &err);
352 
353 	SDT_PROBE1(fusefs, , vfsops, mntopts, mntopts);
354 
355 	if (mp->mnt_flag & MNT_UPDATE) {
356 		return fuse_vfs_remount(mp, td, mntopts, max_read,
357 			daemon_timeout);
358 	}
359 
360 	/* `from' contains the device name (eg. /dev/fuse0); REQUIRED */
361 	fspec = vfs_getopts(opts, "from", &err);
362 	if (!fspec)
363 		return err;
364 
365 	/* `fd' contains the filedescriptor for this session; REQUIRED */
366 	if (vfs_scanopt(opts, "fd", "%d", &fd) != 1)
367 		return EINVAL;
368 
369 	err = fuse_getdevice(fspec, td, &fdev);
370 	if (err != 0)
371 		return err;
372 
373 	err = fget(td, fd, &cap_read_rights, &fp);
374 	if (err != 0) {
375 		SDT_PROBE2(fusefs, , vfsops, trace, 1,
376 			"invalid or not opened device");
377 		goto out;
378 	}
379 	fptmp = td->td_fpop;
380 	td->td_fpop = fp;
381 	err = devfs_get_cdevpriv((void **)&data);
382 	td->td_fpop = fptmp;
383 	fdrop(fp, td);
384 	FUSE_LOCK();
385 
386 	if (err != 0 || data == NULL) {
387 		err = ENXIO;
388 		SDT_PROBE4(fusefs, , vfsops, mount_err,
389 			"invalid or not opened device", data, mp, err);
390 		FUSE_UNLOCK();
391 		goto out;
392 	}
393 	if (fdata_get_dead(data)) {
394 		err = ENOTCONN;
395 		SDT_PROBE4(fusefs, , vfsops, mount_err,
396 			"device is dead during mount", data, mp, err);
397 		FUSE_UNLOCK();
398 		goto out;
399 	}
400 	/* Sanity + permission checks */
401 	if (!data->daemoncred)
402 		panic("fuse daemon found, but identity unknown");
403 	if (mntopts & FSESS_DAEMON_CAN_SPY)
404 		err = priv_check(td, PRIV_VFS_FUSE_ALLOWOTHER);
405 	if (err == 0 && td->td_ucred->cr_uid != data->daemoncred->cr_uid)
406 		/* are we allowed to do the first mount? */
407 		err = priv_check(td, PRIV_VFS_FUSE_MOUNT_NONUSER);
408 	if (err) {
409 		FUSE_UNLOCK();
410 		goto out;
411 	}
412 	data->ref++;
413 	data->mp = mp;
414 	data->dataflags |= mntopts;
415 	data->max_read = max_read;
416 	data->daemon_timeout = daemon_timeout;
417 	data->linux_errnos = linux_errnos;
418 	data->mnt_flag = mp->mnt_flag & MNT_UPDATEMASK;
419 	FUSE_UNLOCK();
420 
421 	vfs_getnewfsid(mp);
422 	MNT_ILOCK(mp);
423 	mp->mnt_data = data;
424 	/*
425 	 * FUSE file systems can be either local or remote, but the kernel
426 	 * can't tell the difference.
427 	 */
428 	mp->mnt_flag &= ~MNT_LOCAL;
429 	mp->mnt_kern_flag |= MNTK_USES_BCACHE;
430 	/*
431 	 * Disable nullfs cacheing because it can consume too many resources in
432 	 * the FUSE server.
433 	 */
434 	mp->mnt_kern_flag |= MNTK_NULL_NOCACHE;
435 	MNT_IUNLOCK(mp);
436 	/* We need this here as this slot is used by getnewvnode() */
437 	mp->mnt_stat.f_iosize = maxbcachebuf;
438 	if (subtype) {
439 		strlcat(mp->mnt_stat.f_fstypename, ".", MFSNAMELEN);
440 		strlcat(mp->mnt_stat.f_fstypename, subtype, MFSNAMELEN);
441 	}
442 	memset(mp->mnt_stat.f_mntfromname, 0, MNAMELEN);
443 	strlcpy(mp->mnt_stat.f_mntfromname, fspec, MNAMELEN);
444 	mp->mnt_iosize_max = maxphys;
445 
446 	/* Now handshaking with daemon */
447 	fuse_internal_send_init(data, td);
448 
449 out:
450 	if (err) {
451 		FUSE_LOCK();
452 		if (data != NULL && data->mp == mp) {
453 			/*
454 			 * Destroy device only if we acquired reference to
455 			 * it
456 			 */
457 			SDT_PROBE4(fusefs, , vfsops, mount_err,
458 				"mount failed, destroy device", data, mp, err);
459 			data->mp = NULL;
460 			mp->mnt_data = NULL;
461 			fdata_trydestroy(data);
462 		}
463 		FUSE_UNLOCK();
464 		dev_rel(fdev);
465 	}
466 	return err;
467 }
468 
469 static int
470 fuse_vfsop_unmount(struct mount *mp, int mntflags)
471 {
472 	int err = 0;
473 	int flags = 0;
474 
475 	struct cdev *fdev;
476 	struct fuse_data *data;
477 	struct fuse_dispatcher fdi;
478 	struct thread *td = curthread;
479 
480 	if (mntflags & MNT_FORCE) {
481 		flags |= FORCECLOSE;
482 	}
483 	data = fuse_get_mpdata(mp);
484 	if (!data) {
485 		panic("no private data for mount point?");
486 	}
487 	/* There is 1 extra root vnode reference (mp->mnt_data). */
488 	FUSE_LOCK();
489 	if (data->vroot != NULL) {
490 		struct vnode *vroot = data->vroot;
491 
492 		data->vroot = NULL;
493 		FUSE_UNLOCK();
494 		vrele(vroot);
495 	} else
496 		FUSE_UNLOCK();
497 	err = vflush(mp, 0, flags, td);
498 	if (err) {
499 		return err;
500 	}
501 	if (fdata_get_dead(data)) {
502 		goto alreadydead;
503 	}
504 	if (fsess_maybe_impl(mp, FUSE_DESTROY)) {
505 		fdisp_init(&fdi, 0);
506 		fdisp_make(&fdi, FUSE_DESTROY, mp, 0, td, NULL);
507 
508 		(void)fdisp_wait_answ(&fdi);
509 		fdisp_destroy(&fdi);
510 	}
511 
512 	fdata_set_dead(data);
513 
514 alreadydead:
515 	FUSE_LOCK();
516 	data->mp = NULL;
517 	fdev = data->fdev;
518 	fdata_trydestroy(data);
519 	FUSE_UNLOCK();
520 
521 	MNT_ILOCK(mp);
522 	mp->mnt_data = NULL;
523 	MNT_IUNLOCK(mp);
524 
525 	dev_rel(fdev);
526 
527 	return 0;
528 }
529 
530 SDT_PROBE_DEFINE1(fusefs, , vfsops, invalidate_without_export,
531 	"struct mount*");
532 static int
533 fuse_vfsop_vget(struct mount *mp, ino_t ino, int flags, struct vnode **vpp)
534 {
535 	struct fuse_data *data = fuse_get_mpdata(mp);
536 	uint64_t nodeid = ino;
537 	struct thread *td = curthread;
538 	struct fuse_dispatcher fdi;
539 	struct fuse_entry_out *feo;
540 	struct fuse_vnode_data *fvdat;
541 	const char dot[] = ".";
542 	off_t filesize;
543 	enum vtype vtyp;
544 	int error;
545 
546 	if (!(data->dataflags & FSESS_EXPORT_SUPPORT)) {
547 		/*
548 		 * Unreachable unless you do something stupid, like export a
549 		 * nullfs mount of a fusefs file system.
550 		 */
551 		SDT_PROBE1(fusefs, , vfsops, invalidate_without_export, mp);
552 		return (EOPNOTSUPP);
553 	}
554 
555 	error = fuse_internal_get_cached_vnode(mp, ino, flags, vpp);
556 	if (error || *vpp != NULL)
557 		return error;
558 
559 	/* Do a LOOKUP, using nodeid as the parent and "." as filename */
560 	fdisp_init(&fdi, sizeof(dot));
561 	fdisp_make(&fdi, FUSE_LOOKUP, mp, nodeid, td, td->td_ucred);
562 	memcpy(fdi.indata, dot, sizeof(dot));
563 	error = fdisp_wait_answ(&fdi);
564 
565 	if (error)
566 		return error;
567 
568 	feo = (struct fuse_entry_out *)fdi.answ;
569 	if (feo->nodeid == 0) {
570 		/* zero nodeid means ENOENT and cache it */
571 		error = ENOENT;
572 		goto out;
573 	}
574 
575 	vtyp = IFTOVT(feo->attr.mode);
576 	error = fuse_vnode_get(mp, feo, nodeid, NULL, vpp, NULL, vtyp);
577 	if (error)
578 		goto out;
579 	filesize = feo->attr.size;
580 
581 	/*
582 	 * In the case where we are looking up a FUSE node represented by an
583 	 * existing cached vnode, and the true size reported by FUSE_LOOKUP
584 	 * doesn't match the vnode's cached size, then any cached writes beyond
585 	 * the file's current size are lost.
586 	 *
587 	 * We can get here:
588 	 * * following attribute cache expiration, or
589 	 * * due a bug in the daemon, or
590 	 */
591 	fvdat = VTOFUD(*vpp);
592 	if (vnode_isreg(*vpp) &&
593 	    filesize != fvdat->cached_attrs.va_size &&
594 	    fvdat->flag & FN_SIZECHANGE) {
595 		if (data->cache_mode == fuse_data_cache_mode) {
596 			const char *msg;
597 
598 			if (fuse_libabi_geq(data, 7, 23)) {
599 				msg = "writeback cache incoherent!."
600 				    "To prevent data corruption, disable "
601 				    "the writeback cache according to your "
602 				    "FUSE server's documentation.";
603 			} else {
604 				msg = "writeback cache incoherent!."
605 				    "To prevent data corruption, disable "
606 				    "the writeback cache by setting "
607 				    "vfs.fusefs.data_cache_mode to 0 or 1.";
608 			}
609 			fuse_warn(data, FSESS_WARN_WB_CACHE_INCOHERENT, msg);
610 		} else {
611 			/* If we get here, it's likely a fusefs kernel bug */
612 			printf("%s: WB cache incoherent on %s!\n", __func__,
613 			    vnode_mount(*vpp)->mnt_stat.f_mntonname);
614 		}
615 		fvdat->flag &= ~FN_SIZECHANGE;
616 	}
617 
618 	fuse_internal_cache_attrs(*vpp, &feo->attr, feo->attr_valid,
619 		feo->attr_valid_nsec, NULL);
620 	fuse_validity_2_bintime(feo->entry_valid, feo->entry_valid_nsec,
621 		&fvdat->entry_cache_timeout);
622 out:
623 	fdisp_destroy(&fdi);
624 	return error;
625 }
626 
627 static int
628 fuse_vfsop_root(struct mount *mp, int lkflags, struct vnode **vpp)
629 {
630 	struct fuse_data *data = fuse_get_mpdata(mp);
631 	int err = 0;
632 
633 	if (data->vroot != NULL) {
634 		err = vget(data->vroot, lkflags);
635 		if (err == 0)
636 			*vpp = data->vroot;
637 	} else {
638 		err = fuse_vnode_get(mp, NULL, FUSE_ROOT_ID, NULL, vpp, NULL,
639 		    VDIR);
640 		if (err == 0) {
641 			FUSE_LOCK();
642 			MPASS(data->vroot == NULL || data->vroot == *vpp);
643 			if (data->vroot == NULL) {
644 				SDT_PROBE2(fusefs, , vfsops, trace, 1,
645 					"new root vnode");
646 				data->vroot = *vpp;
647 				FUSE_UNLOCK();
648 				vref(*vpp);
649 			} else if (data->vroot != *vpp) {
650 				SDT_PROBE2(fusefs, , vfsops, trace, 1,
651 					"root vnode race");
652 				FUSE_UNLOCK();
653 				VOP_UNLOCK(*vpp);
654 				vrele(*vpp);
655 				vrecycle(*vpp);
656 				*vpp = data->vroot;
657 			} else
658 				FUSE_UNLOCK();
659 		}
660 	}
661 	return err;
662 }
663 
664 static int
665 fuse_vfsop_statfs(struct mount *mp, struct statfs *sbp)
666 {
667 	struct fuse_dispatcher fdi;
668 	int err = 0;
669 
670 	struct fuse_statfs_out *fsfo;
671 	struct fuse_data *data;
672 
673 	data = fuse_get_mpdata(mp);
674 
675 	if (!(data->dataflags & FSESS_INITED))
676 		goto fake;
677 
678 	fdisp_init(&fdi, 0);
679 	fdisp_make(&fdi, FUSE_STATFS, mp, FUSE_ROOT_ID, NULL, NULL);
680 	err = fdisp_wait_answ(&fdi);
681 	if (err) {
682 		fdisp_destroy(&fdi);
683 		if (err == ENOTCONN) {
684 			/*
685 	                 * We want to seem a legitimate fs even if the daemon
686 	                 * is stiff dead... (so that, eg., we can still do path
687 	                 * based unmounting after the daemon dies).
688 	                 */
689 			goto fake;
690 		}
691 		return err;
692 	}
693 	fsfo = fdi.answ;
694 
695 	sbp->f_blocks = fsfo->st.blocks;
696 	sbp->f_bfree = fsfo->st.bfree;
697 	sbp->f_bavail = fsfo->st.bavail;
698 	sbp->f_files = fsfo->st.files;
699 	sbp->f_ffree = fsfo->st.ffree;	/* cast from uint64_t to int64_t */
700 	sbp->f_namemax = fsfo->st.namelen;
701 	sbp->f_bsize = fsfo->st.frsize;	/* cast from uint32_t to uint64_t */
702 
703 	fdisp_destroy(&fdi);
704 	return 0;
705 
706 fake:
707 	sbp->f_blocks = 0;
708 	sbp->f_bfree = 0;
709 	sbp->f_bavail = 0;
710 	sbp->f_files = 0;
711 	sbp->f_ffree = 0;
712 	sbp->f_namemax = 0;
713 	sbp->f_bsize = S_BLKSIZE;
714 
715 	return 0;
716 }
717