vfs_hash.c

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/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2005 Poul-Henning Kamp
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 */
 
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
 
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/rwlock.h>
#include <sys/vnode.h>
 
static MALLOC_DEFINE(M_VFS_HASH, "vfs_hash", "VFS hash table");
 
static LIST_HEAD(vfs_hash_head, vnode)  *vfs_hash_tbl;
static LIST_HEAD(,vnode)                vfs_hash_side;
static u_long                           vfs_hash_mask;
static struct rwlock __exclusive_cache_line vfs_hash_lock;
 
static void
vfs_hashinit(void *dummy __unused)
{
 
        vfs_hash_tbl = hashinit(desiredvnodes, M_VFS_HASH, &vfs_hash_mask);
        rw_init(&vfs_hash_lock, "vfs hash");
        LIST_INIT(&vfs_hash_side);
}
 
/* Must be SI_ORDER_SECOND so desiredvnodes is available */
SYSINIT(vfs_hash, SI_SUB_VFS, SI_ORDER_SECOND, vfs_hashinit, NULL);
 
u_int
vfs_hash_index(struct vnode *vp)
{
 
        return (vp->v_hash + vp->v_mount->mnt_hashseed);
}
 
static struct vfs_hash_head *
vfs_hash_bucket(const struct mount *mp, u_int hash)
{
 
        return (&vfs_hash_tbl[(hash + mp->mnt_hashseed) & vfs_hash_mask]);
}
 
int
vfs_hash_get(const struct mount *mp, u_int hash, int flags, struct thread *td,
    struct vnode **vpp, vfs_hash_cmp_t *fn, void *arg)
{
        struct vnode *vp;
        enum vgetstate vs;
        int error;
 
        while (1) {
                rw_rlock(&vfs_hash_lock);
                LIST_FOREACH(vp, vfs_hash_bucket(mp, hash), v_hashlist) {
                        if (vp->v_hash != hash)
                                continue;
                        if (vp->v_mount != mp)
                                continue;
                        if (fn != NULL && fn(vp, arg))
                                continue;
                        vs = vget_prep(vp);
                        rw_runlock(&vfs_hash_lock);
                        error = vget_finish(vp, flags, vs);
                        if (error == ENOENT && (flags & LK_NOWAIT) == 0)
                                break;
                        if (error != 0)
                                return (error);
                        if (vp->v_hash != hash ||
                            (fn != NULL && fn(vp, arg))) {
                                vput(vp);
                                /* Restart the bucket walk. */
                                break;
                        }
                        *vpp = vp;
                        return (0);
                }
                if (vp == NULL) {
                        rw_runlock(&vfs_hash_lock);
                        *vpp = NULL;
                        return (0);
                }
        }
}
 
void
vfs_hash_ref(const struct mount *mp, u_int hash, struct thread *td,
    struct vnode **vpp, vfs_hash_cmp_t *fn, void *arg)
{
        struct vnode *vp;
 
        while (1) {
                rw_rlock(&vfs_hash_lock);
                LIST_FOREACH(vp, vfs_hash_bucket(mp, hash), v_hashlist) {
                        if (vp->v_hash != hash)
                                continue;
                        if (vp->v_mount != mp)
                                continue;
                        if (fn != NULL && fn(vp, arg))
                                continue;
                        vhold(vp);
                        rw_runlock(&vfs_hash_lock);
                        vref(vp);
                        vdrop(vp);
                        *vpp = vp;
                        return;
                }
                if (vp == NULL) {
                        rw_runlock(&vfs_hash_lock);
                        *vpp = NULL;
                        return;
                }
        }
}
 
void
vfs_hash_remove(struct vnode *vp)
{
 
        rw_wlock(&vfs_hash_lock);
        LIST_REMOVE(vp, v_hashlist);
        rw_wunlock(&vfs_hash_lock);
}
 
int
vfs_hash_insert(struct vnode *vp, u_int hash, int flags, struct thread *td,
    struct vnode **vpp, vfs_hash_cmp_t *fn, void *arg)
{
        struct vnode *vp2;
        enum vgetstate vs;
        int error;
 
        *vpp = NULL;
        while (1) {
                rw_wlock(&vfs_hash_lock);
                LIST_FOREACH(vp2,
                    vfs_hash_bucket(vp->v_mount, hash), v_hashlist) {
                        if (vp2->v_hash != hash)
                                continue;
                        if (vp2->v_mount != vp->v_mount)
                                continue;
                        if (fn != NULL && fn(vp2, arg))
                                continue;
                        vs = vget_prep(vp2);
                        rw_wunlock(&vfs_hash_lock);
                        error = vget_finish(vp2, flags, vs);
                        if (error == ENOENT && (flags & LK_NOWAIT) == 0)
                                break;
                        rw_wlock(&vfs_hash_lock);
                        LIST_INSERT_HEAD(&vfs_hash_side, vp, v_hashlist);
                        rw_wunlock(&vfs_hash_lock);
                        vgone(vp);
                        vput(vp);
                        if (!error)
                                *vpp = vp2;
                        return (error);
                }
                if (vp2 == NULL)
                        break;
        }
        vp->v_hash = hash;
        LIST_INSERT_HEAD(vfs_hash_bucket(vp->v_mount, hash), vp, v_hashlist);
        rw_wunlock(&vfs_hash_lock);
        return (0);
}
 
void
vfs_hash_rehash(struct vnode *vp, u_int hash)
{
        ASSERT_VOP_ELOCKED(vp, "rehash requires excl lock");
 
        rw_wlock(&vfs_hash_lock);
        LIST_REMOVE(vp, v_hashlist);
        LIST_INSERT_HEAD(vfs_hash_bucket(vp->v_mount, hash), vp, v_hashlist);
        vp->v_hash = hash;
        rw_wunlock(&vfs_hash_lock);
}
 
void
vfs_hash_changesize(u_long newmaxvnodes)
{
        struct vfs_hash_head *vfs_hash_newtbl, *vfs_hash_oldtbl;
        u_long vfs_hash_newmask, vfs_hash_oldmask;
        struct vnode *vp;
        int i;
 
        vfs_hash_newtbl = hashinit(newmaxvnodes, M_VFS_HASH,
                &vfs_hash_newmask);
        /* If same hash table size, nothing to do */
        if (vfs_hash_mask == vfs_hash_newmask) {
                free(vfs_hash_newtbl, M_VFS_HASH);
                return;
        }
        /*
         * Move everything from the old hash table to the new table.
         * None of the vnodes in the table can be recycled because to
         * do so, they have to be removed from the hash table.
         */
        rw_wlock(&vfs_hash_lock);
        vfs_hash_oldtbl = vfs_hash_tbl;
        vfs_hash_oldmask = vfs_hash_mask;
        vfs_hash_tbl = vfs_hash_newtbl;
        vfs_hash_mask = vfs_hash_newmask;
        for (i = 0; i <= vfs_hash_oldmask; i++) {
                while ((vp = LIST_FIRST(&vfs_hash_oldtbl[i])) != NULL) {
                        LIST_REMOVE(vp, v_hashlist);
                        LIST_INSERT_HEAD(
                            vfs_hash_bucket(vp->v_mount, vp->v_hash),
                            vp, v_hashlist);
                }
        }
        rw_wunlock(&vfs_hash_lock);
        free(vfs_hash_oldtbl, M_VFS_HASH);
}