[stat_cache] FAM: improve monitoring, cache 16 sec

improve FAM monitoring to use reference counting in internal cache

revalidate entries upon use after 16 sec to recover from missed events

(see comments in commit for more details about limitations)

src/stat_cache.c

@@ -25,48 +25,18 @@
 #endif
 
 #ifndef HAVE_LSTAT
-# define lstat stat
+#define lstat stat
+#ifndef S_ISLNK
+#define S_ISLNK(mode) (0)
+#endif
 #endif
 
 /*
  * stat-cache
  *
- * we cache the stat() calls in our own storage
- * the directories are cached in FAM
- *
- * if we get a change-event from FAM, we increment the version in the FAM->dir mapping
- *
- * if the stat()-cache is queried we check if the version id for the directory is the
- * same and return immediatly.
- *
- *
- * What we need:
- *
- * - for each stat-cache entry we need a fast indirect lookup on the directory name
- * - for each FAMRequest we have to find the version in the directory cache (index as userdata)
- *
- * stat <<-> directory <-> FAMRequest
- *
- * if file is deleted, directory is dirty, file is rechecked ...
- * if directory is deleted, directory mapping is removed
- *
- * */
-
-/* the directory name is too long to always compare on it
- * - we need a hash
- * - the hash-key is used as sorting criteria for a tree
  * - a splay-tree is used as we can use the caching effect of it
  */
 
-/* we want to cleanup the FAM stat-cache every few seconds, let's say 10
- *
- * - (NOT CURRENTLY DONE)
- * - remove entries which are outdated since 30s
- * - remove entries which are fresh but havn't been used since 60s
- * - if we don't have a stat-cache entry for a directory, release it from the monitor
- */
-
-
 enum {
   STAT_CACHE_ENGINE_UNSET,
   STAT_CACHE_ENGINE_NONE,
@@ -74,15 +44,11 @@ enum {
   STAT_CACHE_ENGINE_FAM
 };
 
-#ifdef HAVE_FAM_H
-struct stat_cache_fam;
-#endif
+struct stat_cache_fam;  /* declaration */
 
 typedef struct stat_cache {
-	splay_tree *files; /* the nodes of the tree are stat_cache_entry's */
-      #ifdef HAVE_FAM_H
+	splay_tree *files; /* nodes of tree are (stat_cache_entry *) */
 	struct stat_cache_fam *scf;
-      #endif
 } stat_cache;
 
 
@@ -115,56 +81,107 @@ static void * stat_cache_sptree_find(splay_tree ** const sptree,
 
 #ifdef HAVE_FAM_H
 
+/* monitor changes in directories using FAM
+ *
+ * This implementation employing FAM monitors directories as they are used,
+ * and maintains a reference count for cache use within stat_cache.c.
+ * A periodic job runs in lighttpd every 32 seconds, expiring entires unused
+ * in last 64 seconds out of the cache and cancelling FAM monitoring.  Items
+ * within the cache are checked against the filesystem upon use if last stat()
+ * was greater than or equal to 16 seconds ago.
+ *
+ * This implementation does not monitor every directory in a tree, and therefore
+ * the cache may get out-of-sync with the filesystem.  Delays in receiving and
+ * processing events from FAM might also lead to stale cache entries.
+ *
+ * For many websites, a large number of files are seldom, if ever, modified,
+ * and a common practice with images is to create a new file with a new name
+ * when a new version is needed, in order for client browsers and CDNs to better
+ * cache the content.  Given this, most use will see little difference in
+ * performance between server.stat-cache-engine = "fam" and "simple" (default).
+ * The default server.stat-cache-engine = "simple" calls stat() on a target once
+ * per second, and reuses that information until the next second.  For use where
+ * changes must be immediately visible, server.stat-cache-engine = "disable"
+ * should be used.
+ *
+ * When considering use of server.stat-cache-engine = "fam", there are a few
+ * additional limitations for this cache implementation using FAM.
+ * - symlinks to files located outside of the current directory do not result
+ *   in changes to that file being monitored (unless that file is in a directory
+ *   which is monitored as a result of a different request).  symlinks can be
+ *   chained and can be circular.  This implementation *does not* readlink() or
+ *   realpath() to resolve the chains to find and monitor the ultimate target
+ *   directory.  While symlinks to files located outside the current directory
+ *   are not monitored, symlinks to directories *are* monitored, though chains
+ *   of symlinks to directories do not result in monitoring of the directories
+ *   containing intermediate symlinks to the target directory.
+ * - directory rename of a directory which is not currently being monitored will
+ *   result in stale information in the cache if there is a subdirectory that is
+ *   being monitored.
+ * Even though lighttpd will not receive FAM events in the above cases, lighttpd
+ * does re-validate the information in the cache upon use if the cache entry has
+ * not been checked in 16 seconds, so that is the upper limit for use of stale
+ * data.
+ *
+ * Use of server.stat-cache-engine = "fam" is discouraged for extremely volatile
+ * directories such as temporary directories (e.g. /tmp and maybe /var/tmp) due
+ * to the overhead of processing the additional noise generated from changes.
+ * Related, server.stat-cache-engine = "fam" is not recommended on trees of
+ * untrusted files where a malicious user could generate an excess of change
+ * events.
+ *
+ * Internal note: lighttpd walks the caches to prune trees in stat_cache when an
+ * event is received for a directory (or symlink to a directory) which has been
+ * deleted or renamed.  The splaytree data structure is suboptimal for frequent
+ * changes of large directories trees where there have been a large number of
+ * different files recently accessed and part of the stat_cache.
+ */
+
 #include <fam.h>
 
-typedef struct {
+typedef struct fam_dir_entry {
 	buffer *name;
-	int version;
+	int refcnt;
 	FAMRequest req;
+	time_t stat_ts;
+	dev_t st_dev;
+	ino_t st_ino;
+	struct fam_dir_entry *fam_parent;
 } fam_dir_entry;
 
 typedef struct stat_cache_fam {
 	splay_tree *dirs; /* the nodes of the tree are fam_dir_entry */
-
 	FAMConnection fam;
-
-	int dir_ndx;
-	fam_dir_entry *fam_dir;
-	size_t dirlen; /* for building the dirname from the filename */
 	fdnode *fdn;
 	int fd;
 } stat_cache_fam;
 
-static fam_dir_entry * fam_dir_entry_init(void) {
-	fam_dir_entry *fam_dir = NULL;
-
-	fam_dir = calloc(1, sizeof(*fam_dir));
-	force_assert(NULL != fam_dir);
+static fam_dir_entry * fam_dir_entry_init(const char *name, size_t len)
+{
+    fam_dir_entry * const fam_dir = calloc(1, sizeof(*fam_dir));
+    force_assert(NULL != fam_dir);
 
-	fam_dir->name = buffer_init();
+    fam_dir->name = buffer_init();
+    buffer_copy_string_len(fam_dir->name, name, len);
+    fam_dir->refcnt = 0;
 
-	return fam_dir;
+    return fam_dir;
 }
 
-static void fam_dir_entry_free(FAMConnection *fc, void *data) {
-	fam_dir_entry *fam_dir = data;
-
-	if (!fam_dir) return;
-
-	FAMCancelMonitor(fc, &fam_dir->req);
-
-	buffer_free(fam_dir->name);
-	free(fam_dir);
+static void fam_dir_entry_free(fam_dir_entry *fam_dir)
+{
+    if (!fam_dir) return;
+    /*(fam_dir->parent might be invalid pointer here; ignore)*/
+    buffer_free(fam_dir->name);
+    free(fam_dir);
 }
 
-static void fam_dir_node_delete(stat_cache_fam *scf, const char *name, size_t len)
+static void fam_dir_invalidate_node(fam_dir_entry *fam_dir)
 {
-    splay_tree **sptree = &scf->dirs;
-    fam_dir_entry *fam_dir =
-      stat_cache_sptree_find(sptree, name, len);
-    if (fam_dir && buffer_is_equal_string(fam_dir->name, name, len)) {
-        fam_dir_entry_free(&scf->fam, fam_dir);
-        *sptree = splaytree_delete(*sptree, (*sptree)->key);
+    fam_dir->stat_ts = 0;
+    if (fam_dir->fam_parent) {
+        --fam_dir->fam_parent->refcnt;
+        fam_dir->fam_parent = NULL;
     }
 }
 
@@ -173,43 +190,58 @@ static void fam_dir_node_delete(stat_cache_fam *scf, const char *name, size_t le
  * remove tagged entries in a second loop
  */
 
-static void fam_dir_tag_tree(splay_tree *t, const char *name, size_t len,
-                             int *keys, int *ndx)
+static void fam_dir_tag_refcnt(splay_tree *t, int *keys, int *ndx)
 {
     if (*ndx == 8192) return; /*(must match num array entries in keys[])*/
-    if (t->left)  fam_dir_tag_tree(t->left,  name, len, keys, ndx);
-    if (t->right) fam_dir_tag_tree(t->right, name, len, keys, ndx);
+    if (t->left)  fam_dir_tag_refcnt(t->left,  keys, ndx);
+    if (t->right) fam_dir_tag_refcnt(t->right, keys, ndx);
     if (*ndx == 8192) return; /*(must match num array entries in keys[])*/
 
-    buffer *b = ((fam_dir_entry *)t->data)->name;
-    size_t blen = buffer_string_length(b);
-    if (blen > len && b->ptr[len] == '/' && 0 == memcmp(b->ptr, name, len))
+    fam_dir_entry * const fam_dir = t->data;
+    if (0 == fam_dir->refcnt) {
+        fam_dir_invalidate_node(fam_dir);
         keys[(*ndx)++] = t->key;
+    }
 }
 
-static void fam_dir_prune_tree(stat_cache_fam * const scf,
-                               const char *name, size_t len)
-{
+static void fam_dir_periodic_cleanup(server *srv) {
     int max_ndx, i;
     int keys[8192]; /* 32k size on stack */
+    stat_cache_fam * const scf = srv->stat_cache->scf;
     do {
         if (!scf->dirs) return;
         max_ndx = 0;
-        fam_dir_tag_tree(scf->dirs, name, len, keys, &max_ndx);
+        fam_dir_tag_refcnt(scf->dirs, keys, &max_ndx);
         for (i = 0; i < max_ndx; ++i) {
             const int ndx = keys[i];
             splay_tree *node = scf->dirs = splaytree_splay(scf->dirs, ndx);
             if (node && node->key == ndx) {
-                fam_dir_entry_free(&scf->fam, node->data);
+                fam_dir_entry *fam_dir = node->data;
                 scf->dirs = splaytree_delete(scf->dirs, ndx);
+                FAMCancelMonitor(&scf->fam, &fam_dir->req);
+                fam_dir_entry_free(fam_dir);
             }
         }
     } while (max_ndx == sizeof(keys)/sizeof(int));
 }
 
+static void fam_dir_invalidate_tree(splay_tree *t, const char *name, size_t len)
+{
+    /*force_assert(t);*/
+    if (t->left)  fam_dir_invalidate_tree(t->left,  name, len);
+    if (t->right) fam_dir_invalidate_tree(t->right, name, len);
+
+    fam_dir_entry * const fam_dir = t->data;
+    buffer *b = fam_dir->name;
+    size_t blen = buffer_string_length(b);
+    if (blen > len && b->ptr[len] == '/' && 0 == memcmp(b->ptr, name, len))
+        fam_dir_invalidate_node(fam_dir);
+}
+
 /* declarations */
 static void stat_cache_delete_tree(server *srv, const char *name, size_t len);
 static void stat_cache_invalidate_entry(server *srv, const char *name, size_t len);
+static void stat_cache_invalidate_dir_tree(server *srv, const char *name, size_t len);
 
 static handler_t stat_cache_handle_fdevent(server *srv, void *_fce, int revent) {
 	stat_cache_fam *scf = srv->stat_cache->scf;
@@ -234,47 +266,65 @@ static handler_t stat_cache_handle_fdevent(server *srv, void *_fce, int revent)
 			}
 
 			if (fe.filename[0] != '/') {
+				buffer * const n = fam_dir->name;
+				fam_dir_entry *fam_link;
 				size_t len;
 				switch(fe.code) {
 				case FAMCreated:
-					/* file created in monitored dir modifies dir */
-					++fam_dir->version;
-					break;
+					/* file created in monitored dir modifies dir and
+					 * we should get a separate FAMChanged event for dir.
+					 * Therefore, ignore file FAMCreated event here.
+					 * Also, if FAMNoExists() is used, might get spurious
+					 * FAMCreated events as changes are made e.g. in monitored
+					 * sub-sub-sub dirs and the library discovers new (already
+					 * existing) dir entries */
+					continue;
 				case FAMChanged:
 					/* file changed in monitored dir does not modify dir */
-					++fam_dir->version; /* however, current impl here needs this */
 				case FAMDeleted:
 				case FAMMoved:
 					/* file deleted or moved in monitored dir modifies dir,
 					 * but FAM provides separate notification for that */
-					++fam_dir->version;
+
 					/* temporarily append filename to dir in fam_dir->name to
 					 * construct path, then delete stat_cache entry (if any)*/
-					len = buffer_string_length(fam_dir->name);
-					buffer_append_string_len(fam_dir->name, CONST_STR_LEN("/"));
-					buffer_append_string_len(fam_dir->name, fe.filename, strlen(fe.filename));
+					len = buffer_string_length(n);
+					buffer_append_string_len(n, CONST_STR_LEN("/"));
+					buffer_append_string_len(n,fe.filename,strlen(fe.filename));
 					/* (alternatively, could chose to stat() and update)*/
-					stat_cache_invalidate_entry(srv, CONST_BUF_LEN(fam_dir->name));
-					buffer_string_set_length(fam_dir->name, len);
-					break;
+					stat_cache_invalidate_entry(srv, CONST_BUF_LEN(n));
+
+					fam_link = /*(check if might be symlink to monitored dir)*/
+					  stat_cache_sptree_find(&scf->dirs, CONST_BUF_LEN(n));
+					if (fam_link && !buffer_is_equal(fam_link->name, n))
+						fam_link = NULL;
+
+					buffer_string_set_length(n, len);
+
+					if (fam_link) {
+						/* replaced symlink changes containing dir */
+						stat_cache_invalidate_entry(srv, CONST_BUF_LEN(n));
+						/* handle symlink to dir as deleted dir below */
+						fe.code = FAMDeleted;
+						fam_dir = fam_link;
+						break;
+					}
+					continue;
 				default:
-					break;
+					continue;
 				}
-				continue;
 			}
 
-			/*expect: buffer_is_equal_string(fam_dir->name, fe.filename, strlen(fe.filename))*/
 			switch(fe.code) {
 			case FAMChanged:
-				++fam_dir->version;
 				stat_cache_invalidate_entry(srv, CONST_BUF_LEN(fam_dir->name));
 				break;
 			case FAMDeleted:
 			case FAMMoved:
-				scf->dirs = splaytree_delete(scf->dirs, ndx);
-				fam_dir_prune_tree(scf, CONST_BUF_LEN(fam_dir->name));
 				stat_cache_delete_tree(srv, CONST_BUF_LEN(fam_dir->name));
-				fam_dir_entry_free(&scf->fam, fam_dir);
+				fam_dir_invalidate_node(fam_dir);
+				fam_dir_invalidate_tree(scf->dirs, CONST_BUF_LEN(fam_dir->name));
+				fam_dir_periodic_cleanup(srv);
 				break;
 			default:
 				break;
@@ -297,6 +347,7 @@ static handler_t stat_cache_handle_fdevent(server *srv, void *_fce, int revent)
 
 static stat_cache_fam * stat_cache_init_fam(server *srv) {
 	stat_cache_fam *scf = calloc(1, sizeof(*scf));
+	force_assert(scf);
 	scf->fd = -1;
 
 	/* setup FAM */
@@ -321,8 +372,9 @@ static void stat_cache_free_fam(stat_cache_fam *scf) {
 	if (NULL == scf) return;
 
 	while (scf->dirs) {
+		/*(skip entry invalidation and FAMCancelMonitor())*/
 		splay_tree *node = scf->dirs;
-		fam_dir_entry_free(&scf->fam, node->data);
+		fam_dir_entry_free((fam_dir_entry *)node->data);
 		scf->dirs = splaytree_delete(scf->dirs, node->key);
 	}
 
@@ -335,77 +387,123 @@ static void stat_cache_free_fam(stat_cache_fam *scf) {
 	free(scf);
 }
 
-static handler_t stat_cache_fam_dir_check(server *srv, stat_cache_fam *scf, stat_cache_entry *sce, const buffer *name) {
-	char *slash = !buffer_string_is_empty(name)
-          ? strrchr(name->ptr, '/')
-          : NULL;
-	if (NULL == slash) {
-		log_error_write(srv, __FILE__, __LINE__, "sb",
-				"no '/' found in filename:", name);
-		return HANDLER_ERROR;
-	}
-	scf->dirlen = (size_t)(slash - name->ptr);
-	if (0 == scf->dirlen) scf->dirlen = 1; /* root dir ("/") */
-
-	scf->dir_ndx = hashme(name->ptr, scf->dirlen);
-
-	scf->dirs = splaytree_splay(scf->dirs, scf->dir_ndx);
-
-	if ((NULL != scf->dirs) && (scf->dirs->key == scf->dir_ndx)) {
-		scf->fam_dir = scf->dirs->data;
-
-		/* check whether we got a collision */
-		if (buffer_is_equal_string(scf->fam_dir->name, name->ptr, scf->dirlen)) {
-			/* test whether a found file cache entry is still ok */
-			if ((NULL != sce) && (scf->fam_dir->version == sce->dir_version)) {
-				/* the stat()-cache entry is still ok */
-				return HANDLER_FINISHED;
-			}
-		} else {
-			/* hash collision, forget about the entry */
-			scf->fam_dir = NULL;
-		}
-	} else {
-		scf->fam_dir = NULL;
-	}
-
-	return HANDLER_GO_ON;
-}
+static fam_dir_entry * fam_dir_monitor(server *srv, stat_cache_fam *scf, char *fn, size_t dirlen, struct stat *st)
+{
+    const int fn_is_dir = S_ISDIR(st->st_mode);
+    /*force_assert(0 != dirlen);*/
+    /*force_assert(fn[0] == '/');*/
+    /* consistency: ensure fn does not end in '/' unless root "/"
+     * FAM events will not end in '/', so easier to match this way */
+    if (fn[dirlen-1] == '/') --dirlen;
+    if (0 == dirlen) dirlen = 1; /* root dir ("/") */
+    /* Note: paths are expected to be normalized before calling stat_cache,
+     * e.g. without repeated '/' */
+    if (!fn_is_dir) {
+        while (fn[--dirlen] != '/') ;
+        if (0 == dirlen) dirlen = 1; /*(should not happen for file)*/
+    }
+    int dir_ndx = hashme(fn, dirlen);
+    fam_dir_entry *fam_dir = NULL;
+
+    scf->dirs = splaytree_splay(scf->dirs, dir_ndx);
+    if (NULL != scf->dirs && scf->dirs->key == dir_ndx) {
+        fam_dir = scf->dirs->data;
+        if (!buffer_is_equal_string(fam_dir->name, fn, dirlen)) {
+            /* hash collision; preserve existing
+             * do not monitor new to avoid cache thrashing */
+            return NULL;
+        }
+        /* directory already registered */
+    }
 
-static void stat_cache_fam_dir_monitor(server *srv, stat_cache_fam *scf, stat_cache_entry *sce, const buffer *name) {
-	/* is this directory already registered ? */
-	fam_dir_entry *fam_dir = scf->fam_dir;
-	if (NULL == fam_dir) {
-		/* already splayed scf->dir_ndx */
-		if (NULL != scf->dirs && scf->dirs->key == scf->dir_ndx) {
-			/* hash collision; preserve existing
-			 * do not monitor new to avoid cache thrashing */
-			return;
-		} else {
-			fam_dir = fam_dir_entry_init();
-			scf->dirs = splaytree_insert(scf->dirs, scf->dir_ndx, fam_dir);
-		}
+    struct stat lst;
+    int ck_dir = fn_is_dir;
+    if (!fn_is_dir && (NULL==fam_dir || srv->cur_ts - fam_dir->stat_ts >= 16)) {
+        ck_dir = 1;
+        /*(temporarily modify fn)*/
+        fn[dirlen] = '\0';
+        if (0 != lstat(fn, &lst)) {
+            fn[dirlen] = '/';
+            return NULL;
+        }
+        if (!S_ISLNK(lst.st_mode)) {
+            st = &lst;
+        }
+        else if (0 != stat(fn, st)) { /*st passed in now is stat() of dir*/
+            fn[dirlen] = '/';
+            return NULL;
+        }
+        fn[dirlen] = '/';
+    }
 
-		buffer_copy_string_len(fam_dir->name, name->ptr, scf->dirlen);
-		fam_dir->version = 1;
+    int ck_lnk = (NULL == fam_dir);
+    if (ck_dir && NULL != fam_dir) {
+        /* check stat() matches device and inode, just in case an external event
+         * not being monitored occurs (e.g. rename of unmonitored parent dir)*/
+        if (st->st_dev != fam_dir->st_dev || st->st_ino != fam_dir->st_ino) {
+            ck_lnk = 1;
+            /*(modifies scf->dirs but no need to re-splay for dir_ndx since
+             * fam_dir is not NULL and so splaytree_insert not called below)*/
+            if (scf->dirs) fam_dir_invalidate_tree(scf->dirs, fn, dirlen);
+            if (!fn_is_dir) /*(if dir, caller is updating stat_cache_entry)*/
+                stat_cache_update_entry(srv, fn, dirlen, st, NULL);
+            /*(must not delete tree since caller is holding a valid node)*/
+            stat_cache_invalidate_dir_tree(srv, fn, dirlen);
+            if (0 != FAMCancelMonitor(&scf->fam, &fam_dir->req)
+                || 0 != FAMMonitorDirectory(&scf->fam, fam_dir->name->ptr,
+                                            &fam_dir->req,
+                                            (void *)(intptr_t)dir_ndx)) {
+                fam_dir->stat_ts = 0; /* invalidate */
+                return NULL;
+            }
+            fam_dir->st_dev = st->st_dev;
+            fam_dir->st_ino = st->st_ino;
+        }
+        fam_dir->stat_ts = srv->cur_ts;
+    }
 
-		if (0 != FAMMonitorDirectory(&scf->fam, fam_dir->name->ptr,
-					     &fam_dir->req, (void *)(intptr_t)scf->dir_ndx)) {
+    if (NULL == fam_dir) {
+        fam_dir = fam_dir_entry_init(fn, dirlen);
+
+        if (0 != FAMMonitorDirectory(&scf->fam,fam_dir->name->ptr,&fam_dir->req,
+                                     (void *)(intptr_t)dir_ndx)) {
+            log_error_write(srv, __FILE__, __LINE__, "sbsss",
+                    "monitoring dir failed:",
+                    fam_dir->name,
+                    "file:", fn,
+                    FamErrlist[FAMErrno]);
+            fam_dir_entry_free(fam_dir);
+            return NULL;
+        }
 
-			log_error_write(srv, __FILE__, __LINE__, "sbsbs",
-					"monitoring dir failed:",
-					fam_dir->name,
-					"file:", name,
-					FamErrlist[FAMErrno]);
+        scf->dirs = splaytree_insert(scf->dirs, dir_ndx, fam_dir);
+        fam_dir->stat_ts= srv->cur_ts;
+        fam_dir->st_dev = st->st_dev;
+        fam_dir->st_ino = st->st_ino;
+    }
 
-			scf->dirs = splaytree_delete(scf->dirs, scf->dir_ndx);
-			fam_dir_entry_free(&scf->fam, fam_dir);
-			return;
-		}
-	}
+    if (ck_lnk) {
+        if (fn_is_dir) {
+            /*(temporarily modify fn)*/
+            char e = fn[dirlen];
+            fn[dirlen] = '\0';
+            if (0 != lstat(fn, &lst)) {
+                fn[dirlen] = e;
+                return NULL;
+            }
+            fn[dirlen] = e;
+        }
+        if (fam_dir->fam_parent) {
+            --fam_dir->fam_parent->refcnt;
+            fam_dir->fam_parent = NULL;
+        }
+        if (S_ISLNK(lst.st_mode)) {
+            fam_dir->fam_parent = fam_dir_monitor(srv, scf, fn, dirlen, &lst);
+        }
+    }
 
-	/* bind the fam_fc to the stat() cache entry */
-	sce->dir_version = fam_dir->version;
+    ++fam_dir->refcnt;
+    return fam_dir;
 }
 
 #endif
@@ -448,6 +546,12 @@ static void stat_cache_entry_free(void *data) {
 	stat_cache_entry *sce = data;
 	if (!sce) return;
 
+      #ifdef HAVE_FAM_H
+	/*(decrement refcnt only;
+	 * defer cancelling FAM monitor on dir even if refcnt reaches zero)*/
+	if (sce->fam_dir) --((fam_dir_entry *)sce->fam_dir)->refcnt;
+      #endif
+
 	buffer_free(sce->etag);
 	buffer_free(sce->name);
 	buffer_free(sce->content_type);
@@ -619,8 +723,11 @@ void stat_cache_update_entry(server *srv, const char *name, size_t len,
       stat_cache_sptree_find(sptree, name, len);
     if (sce && buffer_is_equal_string(sce->name, name, len)) {
         sce->stat_ts = srv->cur_ts;
-        sce->st = *st;
-        buffer_copy_buffer(sce->etag, etagb);
+        sce->st = *st; /* etagb might be NULL to clear etag (invalidate) */
+        buffer_copy_string_len(sce->etag, CONST_BUF_LEN(etagb));
+      #if defined(HAVE_XATTR) || defined(HAVE_EXTATTR)
+        buffer_clear(sce->content_type);
+      #endif
     }
 }
 
@@ -637,15 +744,52 @@ void stat_cache_delete_entry(server *srv, const char *name, size_t len)
     }
 }
 
+#if HAVE_FAM_H
+
 static void stat_cache_invalidate_entry(server *srv, const char *name, size_t len)
 {
     splay_tree **sptree = &srv->stat_cache->files;
     stat_cache_entry *sce = stat_cache_sptree_find(sptree, name, len);
     if (sce && buffer_is_equal_string(sce->name, name, len)) {
         sce->stat_ts = 0;
+      #ifdef HAVE_FAM_H
+        if (sce->fam_dir != NULL) {
+            --((fam_dir_entry *)sce->fam_dir)->refcnt;
+            sce->fam_dir = NULL;
+        }
+      #endif
     }
 }
 
+static void stat_cache_invalidate_dir_tree_walk(splay_tree *t,
+                                                const char *name, size_t len)
+{
+    if (t->left)  stat_cache_invalidate_dir_tree_walk(t->left,  name, len);
+    if (t->right) stat_cache_invalidate_dir_tree_walk(t->right, name, len);
+
+    buffer *b = ((stat_cache_entry *)t->data)->name;
+    size_t blen = buffer_string_length(b);
+    if (blen > len && b->ptr[len] == '/' && 0 == memcmp(b->ptr, name, len)) {
+        stat_cache_entry *sce = t->data;
+        sce->stat_ts = 0;
+      #ifdef HAVE_FAM_H
+        if (sce->fam_dir != NULL) {
+            --((fam_dir_entry *)sce->fam_dir)->refcnt;
+            sce->fam_dir = NULL;
+        }
+      #endif
+    }
+}
+
+static void stat_cache_invalidate_dir_tree(server *srv,
+                                           const char *name, size_t len)
+{
+    splay_tree *sptree = srv->stat_cache->files;
+    if (sptree) stat_cache_invalidate_dir_tree_walk(sptree, name, len);
+}
+
+#endif
+
 /*
  * walk though splay_tree and collect contents of dir tree.
  * remove tagged entries in a second loop
@@ -695,13 +839,17 @@ void stat_cache_delete_dir(server *srv, const char *name, size_t len)
 {
     force_assert(0 != len);
     if (name[len-1] == '/') { if (0 == --len) len = 1; }
+    stat_cache_delete_tree(srv, name, len);
   #ifdef HAVE_FAM_H
     if (srv->srvconf.stat_cache_engine == STAT_CACHE_ENGINE_FAM) {
-        fam_dir_node_delete(srv->stat_cache->scf, name, len);
-        fam_dir_prune_tree(srv->stat_cache->scf, name, len);
+        fam_dir_entry *fam_dir =
+          stat_cache_sptree_find(&srv->stat_cache->scf->dirs, name, len);
+        if (fam_dir && buffer_is_equal_string(fam_dir->name, name, len))
+            fam_dir_invalidate_node(fam_dir);
+        fam_dir_invalidate_tree(srv->stat_cache->scf->dirs, name, len);
+        fam_dir_periodic_cleanup(srv);
     }
   #endif
-    stat_cache_delete_tree(srv, name, len);
 }
 
 /***
@@ -761,32 +909,28 @@ handler_t stat_cache_get_entry(server *srv, connection *con, buffer *name, stat_
 					return HANDLER_GO_ON;
 				}
 			}
+		      #ifdef HAVE_FAM_H
+			else if (srv->srvconf.stat_cache_engine == STAT_CACHE_ENGINE_FAM
+				 && sce->fam_dir) { /* entry is in monitored dir */
+				/* re-stat() periodically, even if monitoring for changes
+				 * (due to limitations in stat_cache.c use of FAM)
+				 * (gaps due to not continually monitoring an entire tree) */
+				if (srv->cur_ts - sce->stat_ts < 16) {
+					if (final_slash && !S_ISDIR(sce->st.st_mode)) {
+						errno = ENOTDIR;
+						return HANDLER_ERROR;
+					}
+					*ret_sce = sce;
+					return HANDLER_GO_ON;
+				}
+			}
+		      #endif
 		} else {
 			/* collision, forget about the entry */
 			sce = NULL;
 		}
 	}
 
-#ifdef HAVE_FAM_H
-	/* dir-check */
-	if (srv->srvconf.stat_cache_engine == STAT_CACHE_ENGINE_FAM) {
-		switch (stat_cache_fam_dir_check(srv, sc->scf, sce, name)) {
-		case HANDLER_GO_ON:
-			break;
-		case HANDLER_FINISHED:
-			if (final_slash && !S_ISDIR(sce->st.st_mode)) {
-				errno = ENOTDIR;
-				return HANDLER_ERROR;
-			}
-			*ret_sce = sce;
-			return HANDLER_GO_ON;
-		case HANDLER_ERROR:
-		default:
-			return HANDLER_ERROR;
-		}
-	}
-#endif
-
 	if (-1 == stat(name->ptr, &st)) {
 		return HANDLER_ERROR;
 	}
@@ -822,15 +966,23 @@ handler_t stat_cache_get_entry(server *srv, connection *con, buffer *name, stat_
 
 	}
 
-	sce->st = st;
-	sce->stat_ts = srv->cur_ts;
+	sce->st = st; /*(copy prior to calling fam_dir_monitor())*/
 
 #ifdef HAVE_FAM_H
 	if (srv->srvconf.stat_cache_engine == STAT_CACHE_ENGINE_FAM) {
-		stat_cache_fam_dir_monitor(srv, sc->scf, sce, name);
+		if (sce->fam_dir) --((fam_dir_entry *)sce->fam_dir)->refcnt;
+		sce->fam_dir =
+		  fam_dir_monitor(srv, sc->scf, CONST_BUF_LEN(name), &st);
+	      #if 0 /*(performed below)*/
+		if (NULL != sce->fam_dir) {
+			/*(may have been invalidated by dir change)*/
+			sce->stat_ts = srv->cur_ts;
+		}
+	      #endif
 	}
 #endif
 
+	sce->stat_ts = srv->cur_ts;
 	*ret_sce = sce;
 
 	return HANDLER_GO_ON;
@@ -958,6 +1110,19 @@ static int stat_cache_periodic_cleanup(server *srv, time_t max_age) {
 int stat_cache_trigger_cleanup(server *srv) {
 	time_t max_age = 2;
 
+      #ifdef HAVE_FAM_H
+	if (srv->srvconf.stat_cache_engine == STAT_CACHE_ENGINE_FAM) {
+		if (srv->cur_ts & 0x1F) return 0;
+		/* once every 32 seconds (0x1F == 31) */
+		max_age = 32;
+		fam_dir_periodic_cleanup(srv);
+		/* By doing this before stat_cache_periodic_cleanup(),
+		 * entries used within the next max_age secs will remain
+		 * monitored, instead of effectively flushing and
+		 * rebuilding the FAM monitoring every max_age seconds */
+	}
+      #endif
+
 	stat_cache_periodic_cleanup(srv, max_age);
 
 	return 0;

src/stat_cache.h

@@ -21,7 +21,7 @@ typedef struct {
 	time_t stat_ts;
 
 #ifdef HAVE_FAM_H
-	int    dir_version;
+	void *fam_dir;
 #endif
 
 	buffer *content_type;