xref: /freebsd/sys/fs/nullfs/null_subr.c (revision bb15ca603fa442c72dde3f3cb8b46db6970e3950)
1 /*-
2  * Copyright (c) 1992, 1993
3  *	The Regents of the University of California.  All rights reserved.
4  *
5  * This code is derived from software donated to Berkeley by
6  * Jan-Simon Pendry.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  *    notice, this list of conditions and the following disclaimer.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  *    notice, this list of conditions and the following disclaimer in the
15  *    documentation and/or other materials provided with the distribution.
16  * 4. Neither the name of the University nor the names of its contributors
17  *    may be used to endorse or promote products derived from this software
18  *    without specific prior written permission.
19  *
20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30  * SUCH DAMAGE.
31  *
32  *	@(#)null_subr.c	8.7 (Berkeley) 5/14/95
33  *
34  * $FreeBSD$
35  */
36 
37 #include <sys/param.h>
38 #include <sys/systm.h>
39 #include <sys/kernel.h>
40 #include <sys/lock.h>
41 #include <sys/mutex.h>
42 #include <sys/malloc.h>
43 #include <sys/mount.h>
44 #include <sys/proc.h>
45 #include <sys/vnode.h>
46 
47 #include <fs/nullfs/null.h>
48 
49 #define LOG2_SIZEVNODE 8		/* log2(sizeof struct vnode) */
50 #define	NNULLNODECACHE 16
51 
52 /*
53  * Null layer cache:
54  * Each cache entry holds a reference to the lower vnode
55  * along with a pointer to the alias vnode.  When an
56  * entry is added the lower vnode is VREF'd.  When the
57  * alias is removed the lower vnode is vrele'd.
58  */
59 
60 #define	NULL_NHASH(vp) \
61 	(&null_node_hashtbl[(((uintptr_t)vp)>>LOG2_SIZEVNODE) & null_node_hash])
62 
63 static LIST_HEAD(null_node_hashhead, null_node) *null_node_hashtbl;
64 static u_long null_node_hash;
65 struct mtx null_hashmtx;
66 
67 static MALLOC_DEFINE(M_NULLFSHASH, "nullfs_hash", "NULLFS hash table");
68 MALLOC_DEFINE(M_NULLFSNODE, "nullfs_node", "NULLFS vnode private part");
69 
70 static struct vnode * null_hashget(struct mount *, struct vnode *);
71 static struct vnode * null_hashins(struct mount *, struct null_node *);
72 
73 /*
74  * Initialise cache headers
75  */
76 int
77 nullfs_init(vfsp)
78 	struct vfsconf *vfsp;
79 {
80 
81 	NULLFSDEBUG("nullfs_init\n");		/* printed during system boot */
82 	null_node_hashtbl = hashinit(NNULLNODECACHE, M_NULLFSHASH, &null_node_hash);
83 	mtx_init(&null_hashmtx, "nullhs", NULL, MTX_DEF);
84 	return (0);
85 }
86 
87 int
88 nullfs_uninit(vfsp)
89 	struct vfsconf *vfsp;
90 {
91 
92 	mtx_destroy(&null_hashmtx);
93 	free(null_node_hashtbl, M_NULLFSHASH);
94 	return (0);
95 }
96 
97 /*
98  * Return a VREF'ed alias for lower vnode if already exists, else 0.
99  * Lower vnode should be locked on entry and will be left locked on exit.
100  */
101 static struct vnode *
102 null_hashget(mp, lowervp)
103 	struct mount *mp;
104 	struct vnode *lowervp;
105 {
106 	struct null_node_hashhead *hd;
107 	struct null_node *a;
108 	struct vnode *vp;
109 
110 	ASSERT_VOP_LOCKED(lowervp, "null_hashget");
111 
112 	/*
113 	 * Find hash base, and then search the (two-way) linked
114 	 * list looking for a null_node structure which is referencing
115 	 * the lower vnode.  If found, the increment the null_node
116 	 * reference count (but NOT the lower vnode's VREF counter).
117 	 */
118 	hd = NULL_NHASH(lowervp);
119 	mtx_lock(&null_hashmtx);
120 	LIST_FOREACH(a, hd, null_hash) {
121 		if (a->null_lowervp == lowervp && NULLTOV(a)->v_mount == mp) {
122 			/*
123 			 * Since we have the lower node locked the nullfs
124 			 * node can not be in the process of recycling.  If
125 			 * it had been recycled before we grabed the lower
126 			 * lock it would not have been found on the hash.
127 			 */
128 			vp = NULLTOV(a);
129 			vref(vp);
130 			mtx_unlock(&null_hashmtx);
131 			return (vp);
132 		}
133 	}
134 	mtx_unlock(&null_hashmtx);
135 	return (NULLVP);
136 }
137 
138 /*
139  * Act like null_hashget, but add passed null_node to hash if no existing
140  * node found.
141  */
142 static struct vnode *
143 null_hashins(mp, xp)
144 	struct mount *mp;
145 	struct null_node *xp;
146 {
147 	struct null_node_hashhead *hd;
148 	struct null_node *oxp;
149 	struct vnode *ovp;
150 
151 	hd = NULL_NHASH(xp->null_lowervp);
152 	mtx_lock(&null_hashmtx);
153 	LIST_FOREACH(oxp, hd, null_hash) {
154 		if (oxp->null_lowervp == xp->null_lowervp &&
155 		    NULLTOV(oxp)->v_mount == mp) {
156 			/*
157 			 * See null_hashget for a description of this
158 			 * operation.
159 			 */
160 			ovp = NULLTOV(oxp);
161 			vref(ovp);
162 			mtx_unlock(&null_hashmtx);
163 			return (ovp);
164 		}
165 	}
166 	LIST_INSERT_HEAD(hd, xp, null_hash);
167 	mtx_unlock(&null_hashmtx);
168 	return (NULLVP);
169 }
170 
171 static void
172 null_insmntque_dtr(struct vnode *vp, void *xp)
173 {
174 	vp->v_data = NULL;
175 	vp->v_vnlock = &vp->v_lock;
176 	free(xp, M_NULLFSNODE);
177 	vp->v_op = &dead_vnodeops;
178 	(void) vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
179 	vgone(vp);
180 	vput(vp);
181 }
182 
183 /*
184  * Make a new or get existing nullfs node.
185  * Vp is the alias vnode, lowervp is the lower vnode.
186  *
187  * The lowervp assumed to be locked and having "spare" reference. This routine
188  * vrele lowervp if nullfs node was taken from hash. Otherwise it "transfers"
189  * the caller's "spare" reference to created nullfs vnode.
190  */
191 int
192 null_nodeget(mp, lowervp, vpp)
193 	struct mount *mp;
194 	struct vnode *lowervp;
195 	struct vnode **vpp;
196 {
197 	struct null_node *xp;
198 	struct vnode *vp;
199 	int error;
200 
201 	/* Lookup the hash firstly */
202 	*vpp = null_hashget(mp, lowervp);
203 	if (*vpp != NULL) {
204 		vrele(lowervp);
205 		return (0);
206 	}
207 
208 	/*
209 	 * We do not serialize vnode creation, instead we will check for
210 	 * duplicates later, when adding new vnode to hash.
211 	 *
212 	 * Note that duplicate can only appear in hash if the lowervp is
213 	 * locked LK_SHARED.
214 	 */
215 
216 	/*
217 	 * Do the MALLOC before the getnewvnode since doing so afterward
218 	 * might cause a bogus v_data pointer to get dereferenced
219 	 * elsewhere if MALLOC should block.
220 	 */
221 	xp = malloc(sizeof(struct null_node),
222 	    M_NULLFSNODE, M_WAITOK);
223 
224 	error = getnewvnode("null", mp, &null_vnodeops, &vp);
225 	if (error) {
226 		free(xp, M_NULLFSNODE);
227 		return (error);
228 	}
229 
230 	xp->null_vnode = vp;
231 	xp->null_lowervp = lowervp;
232 	vp->v_type = lowervp->v_type;
233 	vp->v_data = xp;
234 	vp->v_vnlock = lowervp->v_vnlock;
235 	if (vp->v_vnlock == NULL)
236 		panic("null_nodeget: Passed a NULL vnlock.\n");
237 	error = insmntque1(vp, mp, null_insmntque_dtr, xp);
238 	if (error != 0)
239 		return (error);
240 	/*
241 	 * Atomically insert our new node into the hash or vget existing
242 	 * if someone else has beaten us to it.
243 	 */
244 	*vpp = null_hashins(mp, xp);
245 	if (*vpp != NULL) {
246 		vrele(lowervp);
247 		vp->v_vnlock = &vp->v_lock;
248 		xp->null_lowervp = NULL;
249 		vrele(vp);
250 		return (0);
251 	}
252 	*vpp = vp;
253 
254 	return (0);
255 }
256 
257 /*
258  * Remove node from hash.
259  */
260 void
261 null_hashrem(xp)
262 	struct null_node *xp;
263 {
264 
265 	mtx_lock(&null_hashmtx);
266 	LIST_REMOVE(xp, null_hash);
267 	mtx_unlock(&null_hashmtx);
268 }
269 
270 #ifdef DIAGNOSTIC
271 
272 struct vnode *
273 null_checkvp(vp, fil, lno)
274 	struct vnode *vp;
275 	char *fil;
276 	int lno;
277 {
278 	struct null_node *a = VTONULL(vp);
279 
280 #ifdef notyet
281 	/*
282 	 * Can't do this check because vop_reclaim runs
283 	 * with a funny vop vector.
284 	 */
285 	if (vp->v_op != null_vnodeop_p) {
286 		printf ("null_checkvp: on non-null-node\n");
287 		panic("null_checkvp");
288 	}
289 #endif
290 	if (a->null_lowervp == NULLVP) {
291 		/* Should never happen */
292 		panic("null_checkvp %p", vp);
293 	}
294 	VI_LOCK_FLAGS(a->null_lowervp, MTX_DUPOK);
295 	if (a->null_lowervp->v_usecount < 1)
296 		panic ("null with unref'ed lowervp, vp %p lvp %p",
297 		    vp, a->null_lowervp);
298 	VI_UNLOCK(a->null_lowervp);
299 #ifdef notyet
300 	printf("null %x/%d -> %x/%d [%s, %d]\n",
301 	        NULLTOV(a), vrefcnt(NULLTOV(a)),
302 		a->null_lowervp, vrefcnt(a->null_lowervp),
303 		fil, lno);
304 #endif
305 	return (a->null_lowervp);
306 }
307 #endif
308