libglusterfs,mount/fuse: implement gidcache mechanism in fuse-bridge

This change genericizes the cache mechanism implemented in commit
8efd2845 into libglusterfs/src/gidcache.[ch] and adds fuse-bridge as
a client. The cache mechanism is fundamentally equivalent, with some
minor changes:

  - Change cache key from uid_t to uint64_t.
  - Modify the cache add logic to locate and use an entry with a
    matching ID, should it already exist. This addresses a bug in
    the existing mechanism where an expired entry supercedes a newly
    added entry in lookup, causing repeated adds and flushing of a
    cache bucket.

The fuse group cache is disabled by default. It can be enabled via
the 'gid-timeout' fuse-bridge translator option and accompanying
mount option (i.e., '-o gid-timeout=1' for a 1s entry timeout).

BUG: 800892
Change-Id: I0b34a2263ca48dbb154790a4a44fc70b733e9114
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-on: http://review.gluster.com/3676
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Reviewed-by: Anand Avati <avati@redhat.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/libglusterfs/src/gidcache.h b/libglusterfs/src/gidcache.h
new file mode 100644
index 000000000..f904f26eb
--- /dev/null
+++ b/libglusterfs/src/gidcache.h
@@ -0,0 +1,52 @@
+/*
+  Copyright (c) 2008-2012 Red Hat, Inc. <http://www.redhat.com>
+  This file is part of GlusterFS.
+
+  This file is licensed to you under your choice of the GNU Lesser
+  General Public License, version 3 or any later version (LGPLv3 or
+  later), or the GNU General Public License, version 2 (GPLv2), in all
+  cases as published by the Free Software Foundation.
+*/
+
+#ifndef __GIDCACHE_H__
+#define __GIDCACHE_H__
+
+#include "glusterfs.h"
+#include "locking.h"
+
+/*
+ * TBD: make the cache size tunable
+ *
+ * The current size represents a pretty trivial amount of memory, and should
+ * provide good hit rates even for quite busy systems.  If we ever want to
+ * support really large cache sizes, we'll need to do dynamic allocation
+ * instead of just defining an array within a private structure. It doesn't make
+ * a whole lot of sense to change the associativity, because it won't improve
+ * hit rates all that much and will increase the maintenance cost as we have
+ * to scan more entries with every lookup/update.
+ */
+
+#define AUX_GID_CACHE_ASSOC     4
+#define AUX_GID_CACHE_BUCKETS   256
+#define AUX_GID_CACHE_SIZE      (AUX_GID_CACHE_ASSOC * AUX_GID_CACHE_BUCKETS)
+
+typedef struct {
+	uint64_t	gl_id;
+	int		gl_count;
+	gid_t		*gl_list;
+	time_t		gl_deadline;
+} gid_list_t;
+
+typedef struct {
+	gf_lock_t	gc_lock;
+	uint32_t	gc_max_age;
+	unsigned int	gc_nbuckets;
+	gid_list_t	gc_cache[AUX_GID_CACHE_SIZE];
+} gid_cache_t;
+
+int gid_cache_init(gid_cache_t *, uint32_t);
+const gid_list_t *gid_cache_lookup(gid_cache_t *, uint64_t);
+void gid_cache_release(gid_cache_t *, const gid_list_t *);
+int gid_cache_add(gid_cache_t *, gid_list_t *);
+
+#endif /* __GIDCACHE_H__ */