DEVFS - rollup, namecache invalidation

* Add convenient way to clean out negative namecache entries by simply
  incrementing a generation number in the mount structure.  Used by DEVFS.

diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c
index ef5c836..7af6f24 100644 (file)
--- a/sys/kern/vfs_cache.c
+++ b/sys/kern/vfs_cache.c
@@ -594,7 +594,7 @@ cache_put(struct nchandle *nch)
  */
 static
 void
-_cache_setvp(struct namecache *ncp, struct vnode *vp)
+_cache_setvp(struct mount *mp, struct namecache *ncp, struct vnode *vp)
 {
        KKASSERT(ncp->nc_flag & NCF_UNRESOLVED);
        ncp->nc_vp = vp;
@@ -626,9 +626,18 @@ _cache_setvp(struct namecache *ncp, struct vnode *vp)
                ++numcache;
                ncp->nc_error = 0;
        } else {
+               /*
+                * When creating a negative cache hit we set the
+                * namecache_gen.  A later resolve will clean out the
+                * negative cache hit if the mount point's namecache_gen
+                * has changed.  Used by devfs, could also be used by
+                * other remote FSs.
+                */
                TAILQ_INSERT_TAIL(&ncneglist, ncp, nc_vnode);
                ++numneg;
                ncp->nc_error = ENOENT;
+               if (mp)
+                       ncp->nc_namecache_gen = mp->mnt_namecache_gen;
        }
        ncp->nc_flag &= ~NCF_UNRESOLVED;
 }
@@ -636,7 +645,7 @@ _cache_setvp(struct namecache *ncp, struct vnode *vp)
 void
 cache_setvp(struct nchandle *nch, struct vnode *vp)
 {
-       _cache_setvp(nch->ncp, vp);
+       _cache_setvp(nch->mount, nch->ncp, vp);
 }
 
 void
@@ -702,6 +711,44 @@ _cache_setunresolved(struct namecache *ncp)
        }
 }
 
+/*
+ * The cache_nresolve() code calls this function to automatically
+ * set a resolved cache element to unresolved if it has timed out
+ * or if it is a negative cache hit and the mount point namecache_gen
+ * has changed.
+ */
+static __inline void
+_cache_auto_unresolve(struct mount *mp, struct namecache *ncp)
+{
+       /*
+        * Already in an unresolved state, nothing to do.
+        */
+       if (ncp->nc_flag & NCF_UNRESOLVED)
+               return;
+
+       /*
+        * Try to zap entries that have timed out.  We have
+        * to be careful here because locked leafs may depend
+        * on the vnode remaining intact in a parent, so only
+        * do this under very specific conditions.
+        */
+       if (ncp->nc_timeout && (int)(ncp->nc_timeout - ticks) < 0 &&
+           TAILQ_EMPTY(&ncp->nc_list)) {
+               _cache_setunresolved(ncp);
+               return;
+       }
+
+       /*
+        * If a resolved negative cache hit is invalid due to
+        * the mount's namecache generation being bumped, zap it.
+        */
+       if (ncp->nc_vp == NULL &&
+           ncp->nc_namecache_gen != mp->mnt_namecache_gen) {
+               _cache_setunresolved(ncp);
+               return;
+       }
+}
+
 void
 cache_setunresolved(struct nchandle *nch)
 {
@@ -1627,7 +1674,7 @@ done:
        vrele(pvp);
        if (rncp.ncp) {
                if (rncp.ncp->nc_flag & NCF_UNRESOLVED) {
-                       _cache_setvp(rncp.ncp, dvp);
+                       _cache_setvp(rncp.mount, rncp.ncp, dvp);
                        if (ncvp_debug >= 2) {
                                kprintf("cache_inefficient_scan: setvp %s/%s = %p\n",
                                        nch->ncp->nc_name, rncp.ncp->nc_name, dvp);
@@ -1812,11 +1859,13 @@ cache_nlookup(struct nchandle *par_nch, struct nlcomponent *nlc)
        struct namecache *ncp;
        struct namecache *new_ncp;
        struct nchashhead *nchpp;
+       struct mount *mp;
        u_int32_t hash;
        globaldata_t gd;
 
        numcalls++;
        gd = mycpu;
+       mp = par_nch->mount;
 
        /*
         * Try to locate an existing entry
@@ -1829,22 +1878,6 @@ restart:
                numchecks++;
 
                /*
-                * Try to zap entries that have timed out.  We have
-                * to be careful here because locked leafs may depend
-                * on the vnode remaining intact in a parent, so only
-                * do this under very specific conditions.
-                */
-               if (ncp->nc_timeout && 
-                   (int)(ncp->nc_timeout - ticks) < 0 &&
-                   (ncp->nc_flag & NCF_UNRESOLVED) == 0 &&
-                   ncp->nc_exlocks == 0 &&
-                   TAILQ_EMPTY(&ncp->nc_list)
-               ) {
-                       cache_zap(_cache_get(ncp));
-                       goto restart;
-               }
-
-               /*
                 * Break out if we find a matching entry.  Note that
                 * UNRESOLVED entries may match, but DESTROYED entries
                 * do not.
@@ -1855,6 +1888,7 @@ restart:
                    (ncp->nc_flag & NCF_DESTROYED) == 0
                ) {
                        if (_cache_get_nonblock(ncp) == 0) {
+                               _cache_auto_unresolve(mp, ncp);
                                if (new_ncp)
                                        _cache_free(new_ncp);
                                goto found;
@@ -1903,7 +1937,7 @@ found:
        else
                ++gd->gd_nchstats->ncs_neghits;
        cache_hysteresis();
-       nch.mount = par_nch->mount;
+       nch.mount = mp;
        nch.ncp = ncp;
        ++nch.mount->mnt_refs;
        return(nch);
@@ -2155,13 +2189,13 @@ cache_resolve_mp(struct mount *mp)
                if (ncp->nc_flag & NCF_UNRESOLVED) {
                        ncp->nc_error = error;
                        if (error == 0) {
-                               _cache_setvp(ncp, vp);
+                               _cache_setvp(mp, ncp, vp);
                                vput(vp);
                        } else {
                                kprintf("[diagnostic] cache_resolve_mp: failed"
                                        " to resolve mount %p err=%d ncp=%p\n",
                                        mp, error, ncp);
-                               _cache_setvp(ncp, NULL);
+                               _cache_setvp(mp, ncp, NULL);
                        }
                } else if (error == 0) {
                        vput(vp);
@@ -2256,7 +2290,7 @@ cache_allocroot(struct nchandle *nch, struct mount *mp, struct vnode *vp)
        nch->mount = mp;
        ++mp->mnt_refs;
        if (vp)
-               _cache_setvp(nch->ncp, vp);
+               _cache_setvp(nch->mount, nch->ncp, vp);
 }
 
 /*

diff --git a/sys/sys/mount.h b/sys/sys/mount.h
index 208b25d..4fc785f 100644 (file)
--- a/sys/sys/mount.h
+++ b/sys/sys/mount.h
@@ -159,7 +159,7 @@ struct mount {
        TAILQ_ENTRY(mount) mnt_list;            /* mount list */
        struct vfsops   *mnt_op;                /* operations on fs */
        struct vfsconf  *mnt_vfc;               /* configuration info */
-       void            *mnt_unused01;
+       long            mnt_namecache_gen;      /* ++ to clear negative hits */
        struct vnode    *mnt_syncer;            /* syncer vnode */
        struct vnodelst mnt_nvnodelist;         /* list of vnodes this mount */
        struct lock     mnt_lock;               /* mount structure lock */

diff --git a/sys/sys/namecache.h b/sys/sys/namecache.h
index 0cf7ef1..1b3124b 100644 (file)
--- a/sys/sys/namecache.h
+++ b/sys/sys/namecache.h
@@ -122,6 +122,7 @@ struct namecache {
     int                nc_exlocks;             /* namespace locking */
     struct thread *nc_locktd;          /* namespace locking */
     int64_t    nc_fsmid;               /* filesystem modified id */
+    long       nc_namecache_gen;       /* cmp against mnt_namecache_gen */
 };
 
 /*