1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2020 Netflix, Inc.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 *
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 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
23 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
24 * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
25 * USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28 #include <sys/param.h>
29 #include <sys/conf.h>
30 #include <sys/mount.h>
31 #include <sys/vnode.h>
32
33 /*
34 * The "mntfs" VCHR vnodes implemented here provide a safe way for file systems
35 * to access their disk devices. Using the normal devfs vnode has the problem
36 * that if the device disappears, the devfs vnode is vgone'd as part of
37 * removing it from the application-visible namespace, and some file systems
38 * (notably FFS with softdep) get very unhappy if their dirty buffers are
39 * invalidated out from under them. By using a separate, private vnode,
40 * file systems are able to clean up their buffer state in a controlled fashion
41 * when the underlying device disappears.
42 */
43
44 static int
mntfs_reclaim(struct vop_reclaim_args * ap)45 mntfs_reclaim(struct vop_reclaim_args *ap)
46 {
47 struct vnode *vp = ap->a_vp;
48
49 dev_rel(vp->v_rdev);
50 return (0);
51 }
52
53 struct vop_vector mntfs_vnodeops = {
54 .vop_default = &default_vnodeops,
55
56 .vop_fsync = vop_stdfsync,
57 .vop_strategy = VOP_PANIC,
58 .vop_reclaim = mntfs_reclaim,
59 };
60 VFS_VOP_VECTOR_REGISTER(mntfs_vnodeops);
61
62 /*
63 * Allocate a private VCHR vnode for use by a mounted fs.
64 * The underlying device will be the same as for the given vnode.
65 * This mntfs vnode must be freed with mntfs_freevp() rather than just
66 * releasing the reference.
67 */
68 struct vnode *
mntfs_allocvp(struct mount * mp,struct vnode * ovp)69 mntfs_allocvp(struct mount *mp, struct vnode *ovp)
70 {
71 struct vnode *vp;
72 struct cdev *dev;
73
74 ASSERT_VOP_ELOCKED(ovp, __func__);
75
76 dev = ovp->v_rdev;
77
78 getnewvnode("mntfs", mp, &mntfs_vnodeops, &vp);
79 vp->v_type = VCHR;
80 vp->v_data = NULL;
81 dev_ref(dev);
82 vp->v_rdev = dev;
83
84 VOP_UNLOCK(ovp);
85 vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
86 vn_set_state(vp, VSTATE_CONSTRUCTED);
87 return (vp);
88 }
89
90 void
mntfs_freevp(struct vnode * vp)91 mntfs_freevp(struct vnode *vp)
92 {
93 ASSERT_VOP_ELOCKED(vp, "mntfs_freevp");
94 vgone(vp);
95 vput(vp);
96 }
97