1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1992, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * This code is derived from software donated to Berkeley by
8 * Jan-Simon Pendry.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of the University nor the names of its contributors
19 * may be used to endorse or promote products derived from this software
20 * without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 *
34 * @(#)null_subr.c 8.7 (Berkeley) 5/14/95
35 *
36 * $FreeBSD$
37 */
38
39 #include <sys/param.h>
40 #include <sys/systm.h>
41 #include <sys/kernel.h>
42 #include <sys/lock.h>
43 #include <sys/rwlock.h>
44 #include <sys/malloc.h>
45 #include <sys/mount.h>
46 #include <sys/proc.h>
47 #include <sys/vnode.h>
48
49 #include <fs/nullfs/null.h>
50
51 /*
52 * Null layer cache:
53 * Each cache entry holds a reference to the lower vnode
54 * along with a pointer to the alias vnode. When an
55 * entry is added the lower vnode is VREF'd. When the
56 * alias is removed the lower vnode is vrele'd.
57 */
58
59 #define NULL_NHASH(vp) (&null_node_hashtbl[vfs_hash_index(vp) & null_hash_mask])
60
61 static LIST_HEAD(null_node_hashhead, null_node) *null_node_hashtbl;
62 static struct rwlock null_hash_lock;
63 static u_long null_hash_mask;
64
65 static MALLOC_DEFINE(M_NULLFSHASH, "nullfs_hash", "NULLFS hash table");
66 MALLOC_DEFINE(M_NULLFSNODE, "nullfs_node", "NULLFS vnode private part");
67
68 static struct vnode * null_hashins(struct mount *, struct null_node *);
69
70 /*
71 * Initialise cache headers
72 */
73 int
74 nullfs_init(vfsp)
75 struct vfsconf *vfsp;
76 {
77
78 null_node_hashtbl = hashinit(desiredvnodes, M_NULLFSHASH,
79 &null_hash_mask);
80 rw_init(&null_hash_lock, "nullhs");
81 return (0);
82 }
83
84 int
85 nullfs_uninit(vfsp)
86 struct vfsconf *vfsp;
87 {
88
89 rw_destroy(&null_hash_lock);
90 hashdestroy(null_node_hashtbl, M_NULLFSHASH, null_hash_mask);
91 return (0);
92 }
93
94 /*
95 * Return a VREF'ed alias for lower vnode if already exists, else 0.
96 * Lower vnode should be locked on entry and will be left locked on exit.
97 */
98 struct vnode *
99 null_hashget(mp, lowervp)
100 struct mount *mp;
101 struct vnode *lowervp;
102 {
103 struct null_node_hashhead *hd;
104 struct null_node *a;
105 struct vnode *vp;
106
107 ASSERT_VOP_LOCKED(lowervp, "null_hashget");
108
109 /*
110 * Find hash base, and then search the (two-way) linked
111 * list looking for a null_node structure which is referencing
112 * the lower vnode. If found, the increment the null_node
113 * reference count (but NOT the lower vnode's VREF counter).
114 */
115 hd = NULL_NHASH(lowervp);
116 rw_rlock(&null_hash_lock);
117 LIST_FOREACH(a, hd, null_hash) {
118 if (a->null_lowervp == lowervp && NULLTOV(a)->v_mount == mp) {
119 /*
120 * Since we have the lower node locked the nullfs
121 * node can not be in the process of recycling. If
122 * it had been recycled before we grabed the lower
123 * lock it would not have been found on the hash.
124 */
125 vp = NULLTOV(a);
126 vref(vp);
127 rw_runlock(&null_hash_lock);
128 return (vp);
129 }
130 }
131 rw_runlock(&null_hash_lock);
132 return (NULLVP);
133 }
134
135 /*
136 * Act like null_hashget, but add passed null_node to hash if no existing
137 * node found.
138 */
139 static struct vnode *
140 null_hashins(mp, xp)
141 struct mount *mp;
142 struct null_node *xp;
143 {
144 struct null_node_hashhead *hd;
145 struct null_node *oxp;
146 struct vnode *ovp;
147
148 hd = NULL_NHASH(xp->null_lowervp);
149 rw_wlock(&null_hash_lock);
150 LIST_FOREACH(oxp, hd, null_hash) {
151 if (oxp->null_lowervp == xp->null_lowervp &&
152 NULLTOV(oxp)->v_mount == mp) {
153 /*
154 * See null_hashget for a description of this
155 * operation.
156 */
157 ovp = NULLTOV(oxp);
158 vref(ovp);
159 rw_wunlock(&null_hash_lock);
160 return (ovp);
161 }
162 }
163 LIST_INSERT_HEAD(hd, xp, null_hash);
164 rw_wunlock(&null_hash_lock);
165 return (NULLVP);
166 }
167
168 static void
169 null_destroy_proto(struct vnode *vp, void *xp)
170 {
171
172 lockmgr(&vp->v_lock, LK_EXCLUSIVE, NULL);
173 VI_LOCK(vp);
174 vp->v_data = NULL;
175 vp->v_vnlock = &vp->v_lock;
176 vp->v_op = &dead_vnodeops;
177 VI_UNLOCK(vp);
178 vgone(vp);
179 vput(vp);
180 free(xp, M_NULLFSNODE);
181 }
182
183 static void
184 null_insmntque_dtr(struct vnode *vp, void *xp)
185 {
186
187 vput(((struct null_node *)xp)->null_lowervp);
188 null_destroy_proto(vp, xp);
189 }
190
191 /*
192 * Make a new or get existing nullfs node.
193 * Vp is the alias vnode, lowervp is the lower vnode.
194 *
195 * The lowervp assumed to be locked and having "spare" reference. This routine
196 * vrele lowervp if nullfs node was taken from hash. Otherwise it "transfers"
197 * the caller's "spare" reference to created nullfs vnode.
198 */
199 int
200 null_nodeget(mp, lowervp, vpp)
201 struct mount *mp;
202 struct vnode *lowervp;
203 struct vnode **vpp;
204 {
205 struct null_node *xp;
206 struct vnode *vp;
207 int error;
208
209 ASSERT_VOP_LOCKED(lowervp, "lowervp");
210 KASSERT(lowervp->v_usecount >= 1, ("Unreferenced vnode %p", lowervp));
211
212 /* Lookup the hash firstly. */
213 *vpp = null_hashget(mp, lowervp);
214 if (*vpp != NULL) {
215 vrele(lowervp);
216 return (0);
217 }
218
219 /*
220 * The insmntque1() call below requires the exclusive lock on
221 * the nullfs vnode. Upgrade the lock now if hash failed to
222 * provide ready to use vnode.
223 */
224 if (VOP_ISLOCKED(lowervp) != LK_EXCLUSIVE) {
225 KASSERT((MOUNTTONULLMOUNT(mp)->nullm_flags & NULLM_CACHE) != 0,
226 ("lowervp %p is not excl locked and cache is disabled",
227 lowervp));
228 vn_lock(lowervp, LK_UPGRADE | LK_RETRY);
229 if ((lowervp->v_iflag & VI_DOOMED) != 0) {
230 vput(lowervp);
231 return (ENOENT);
232 }
233 }
234
235 /*
236 * We do not serialize vnode creation, instead we will check for
237 * duplicates later, when adding new vnode to hash.
238 * Note that duplicate can only appear in hash if the lowervp is
239 * locked LK_SHARED.
240 */
241 xp = malloc(sizeof(struct null_node), M_NULLFSNODE, M_WAITOK);
242
243 error = getnewvnode("nullfs", mp, &null_vnodeops, &vp);
244 if (error) {
245 vput(lowervp);
246 free(xp, M_NULLFSNODE);
247 return (error);
248 }
249
250 xp->null_vnode = vp;
251 xp->null_lowervp = lowervp;
252 xp->null_flags = 0;
253 vp->v_type = lowervp->v_type;
254 vp->v_data = xp;
255 vp->v_vnlock = lowervp->v_vnlock;
256 error = insmntque1(vp, mp, null_insmntque_dtr, xp);
257 if (error != 0)
258 return (error);
259 if (lowervp == MOUNTTONULLMOUNT(mp)->nullm_lowerrootvp)
260 vp->v_vflag |= VV_ROOT;
261
262 /*
263 * Atomically insert our new node into the hash or vget existing
264 * if someone else has beaten us to it.
265 */
266 *vpp = null_hashins(mp, xp);
267 if (*vpp != NULL) {
268 vrele(lowervp);
269 null_destroy_proto(vp, xp);
270 return (0);
271 }
272 *vpp = vp;
273
274 return (0);
275 }
276
277 /*
278 * Remove node from hash.
279 */
280 void
281 null_hashrem(xp)
282 struct null_node *xp;
283 {
284
285 rw_wlock(&null_hash_lock);
286 LIST_REMOVE(xp, null_hash);
287 rw_wunlock(&null_hash_lock);
288 }
289
290 #ifdef DIAGNOSTIC
291
292 struct vnode *
293 null_checkvp(vp, fil, lno)
294 struct vnode *vp;
295 char *fil;
296 int lno;
297 {
298 struct null_node *a = VTONULL(vp);
299
300 #ifdef notyet
301 /*
302 * Can't do this check because vop_reclaim runs
303 * with a funny vop vector.
304 */
305 if (vp->v_op != null_vnodeop_p) {
306 printf ("null_checkvp: on non-null-node\n");
307 panic("null_checkvp");
308 }
309 #endif
310 if (a->null_lowervp == NULLVP) {
311 /* Should never happen */
312 panic("null_checkvp %p", vp);
313 }
314 VI_LOCK_FLAGS(a->null_lowervp, MTX_DUPOK);
315 if (a->null_lowervp->v_usecount < 1)
316 panic ("null with unref'ed lowervp, vp %p lvp %p",
317 vp, a->null_lowervp);
318 VI_UNLOCK(a->null_lowervp);
319 #ifdef notyet
320 printf("null %x/%d -> %x/%d [%s, %d]\n",
321 NULLTOV(a), vrefcnt(NULLTOV(a)),
322 a->null_lowervp, vrefcnt(a->null_lowervp),
323 fil, lno);
324 #endif
325 return (a->null_lowervp);
326 }
327 #endif
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