FS-Cache: Add netfs registration

Add functions to register and unregister a network filesystem or other client
of the FS-Cache service.  This allocates and releases the cookie representing
the top-level index for a netfs, and makes it available to the netfs.

If the FS-Cache facility is disabled, then the calls are optimised away at
compile time.

Note that whilst this patch may appear to work with FS-Cache enabled and a
netfs attempting to use it, it will leak the cookie it allocates for the netfs
as fscache_relinquish_cookie() is implemented in a later patch.  This will
cause the slab code to emit a warning when the module is removed.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Steve Dickson <steved@redhat.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Daire Byrne <Daire.Byrne@framestore.com>

3 files changed, 113 insertions, 2 deletions

diff --git a/fs/fscache/Makefile b/fs/fscache/Makefile
index f88ac1764ce3..ecf6946eaeb3 100644
--- a/fs/fscache/Makefile
+++ b/fs/fscache/Makefile
@@ -6,7 +6,8 @@ fscache-y := \
         cache.o \
         cookie.o \
         fsdef.o \
-        main.o
+        main.o \
+        netfs.o
 
 fscache-$(CONFIG_PROC_FS) += proc.o
 fscache-$(CONFIG_FSCACHE_STATS) += stats.o
diff --git a/fs/fscache/netfs.c b/fs/fscache/netfs.c
new file mode 100644
index 000000000000..e028b8eb1c40
--- /dev/null
+++ b/fs/fscache/netfs.c
@@ -0,0 +1,103 @@
+/* FS-Cache netfs (client) registration
+ *
+ * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#define FSCACHE_DEBUG_LEVEL COOKIE
+#include <linux/module.h>
+#include <linux/slab.h>
+#include "internal.h"
+
+static LIST_HEAD(fscache_netfs_list);
+
+/*
+ * register a network filesystem for caching
+ */
+int __fscache_register_netfs(struct fscache_netfs *netfs)
+{
+        struct fscache_netfs *ptr;
+        int ret;
+
+        _enter("{%s}", netfs->name);
+
+        INIT_LIST_HEAD(&netfs->link);
+
+        /* allocate a cookie for the primary index */
+        netfs->primary_index =
+                kmem_cache_zalloc(fscache_cookie_jar, GFP_KERNEL);
+
+        if (!netfs->primary_index) {
+                _leave(" = -ENOMEM");
+                return -ENOMEM;
+        }
+
+        /* initialise the primary index cookie */
+        atomic_set(&netfs->primary_index->usage, 1);
+        atomic_set(&netfs->primary_index->n_children, 0);
+
+        netfs->primary_index->def               = &fscache_fsdef_netfs_def;
+        netfs->primary_index->parent            = &fscache_fsdef_index;
+        netfs->primary_index->netfs_data        = netfs;
+
+        atomic_inc(&netfs->primary_index->parent->usage);
+        atomic_inc(&netfs->primary_index->parent->n_children);
+
+        spin_lock_init(&netfs->primary_index->lock);
+        INIT_HLIST_HEAD(&netfs->primary_index->backing_objects);
+
+        /* check the netfs type is not already present */
+        down_write(&fscache_addremove_sem);
+
+        ret = -EEXIST;
+        list_for_each_entry(ptr, &fscache_netfs_list, link) {
+                if (strcmp(ptr->name, netfs->name) == 0)
+                        goto already_registered;
+        }
+
+        list_add(&netfs->link, &fscache_netfs_list);
+        ret = 0;
+
+        printk(KERN_NOTICE "FS-Cache: Netfs '%s' registered for caching\n",
+               netfs->name);
+
+already_registered:
+        up_write(&fscache_addremove_sem);
+
+        if (ret < 0) {
+                netfs->primary_index->parent = NULL;
+                __fscache_cookie_put(netfs->primary_index);
+                netfs->primary_index = NULL;
+        }
+
+        _leave(" = %d", ret);
+        return ret;
+}
+EXPORT_SYMBOL(__fscache_register_netfs);
+
+/*
+ * unregister a network filesystem from the cache
+ * - all cookies must have been released first
+ */
+void __fscache_unregister_netfs(struct fscache_netfs *netfs)
+{
+        _enter("{%s.%u}", netfs->name, netfs->version);
+
+        down_write(&fscache_addremove_sem);
+
+        list_del(&netfs->link);
+        fscache_relinquish_cookie(netfs->primary_index, 0);
+
+        up_write(&fscache_addremove_sem);
+
+        printk(KERN_NOTICE "FS-Cache: Netfs '%s' unregistered from caching\n",
+               netfs->name);
+
+        _leave("");
+}
+EXPORT_SYMBOL(__fscache_unregister_netfs);
diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index 9584c094d69f..b195c2e1ef6a 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -173,6 +173,8 @@ struct fscache_netfs {
  * - these are undefined symbols when FS-Cache is not configured and the
  *   optimiser takes care of not using them
  */
+extern int __fscache_register_netfs(struct fscache_netfs *);
+extern void __fscache_unregister_netfs(struct fscache_netfs *);
 extern struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *);
 extern void __fscache_release_cache_tag(struct fscache_cache_tag *);
 
@@ -188,7 +190,10 @@ extern void __fscache_release_cache_tag(struct fscache_cache_tag *);
 static inline
 int fscache_register_netfs(struct fscache_netfs *netfs)
 {
-        return 0;
+        if (fscache_available())
+                return __fscache_register_netfs(netfs);
+        else
+                return 0;
 }
 
 /**
@@ -205,6 +210,8 @@ int fscache_register_netfs(struct fscache_netfs *netfs)
 static inline
 void fscache_unregister_netfs(struct fscache_netfs *netfs)
 {
+        if (fscache_available())
+                __fscache_unregister_netfs(netfs);
 }
 
 /**