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-rw-r--r--Documentation/vm/cleancache.txt4
-rw-r--r--drivers/xen/tmem.c16
-rw-r--r--include/linux/cleancache.h3
-rw-r--r--mm/cleancache.c12
4 files changed, 18 insertions, 17 deletions
diff --git a/Documentation/vm/cleancache.txt b/Documentation/vm/cleancache.txt
index 01d76282444e..e4b49df7a048 100644
--- a/Documentation/vm/cleancache.txt
+++ b/Documentation/vm/cleancache.txt
@@ -28,9 +28,7 @@ IMPLEMENTATION OVERVIEW
A cleancache "backend" that provides transcendent memory registers itself
to the kernel's cleancache "frontend" by calling cleancache_register_ops,
passing a pointer to a cleancache_ops structure with funcs set appropriately.
-Note that cleancache_register_ops returns the previous settings so that
-chaining can be performed if desired. The functions provided must conform to
-certain semantics as follows:
+The functions provided must conform to certain semantics as follows:
Most important, cleancache is "ephemeral". Pages which are copied into
cleancache have an indefinite lifetime which is completely unknowable
diff --git a/drivers/xen/tmem.c b/drivers/xen/tmem.c
index 8a65423bc696..c4211a31612d 100644
--- a/drivers/xen/tmem.c
+++ b/drivers/xen/tmem.c
@@ -397,13 +397,15 @@ static int __init xen_tmem_init(void)
#ifdef CONFIG_CLEANCACHE
BUG_ON(sizeof(struct cleancache_filekey) != sizeof(struct tmem_oid));
if (tmem_enabled && cleancache) {
- char *s = "";
- struct cleancache_ops *old_ops =
- cleancache_register_ops(&tmem_cleancache_ops);
- if (old_ops)
- s = " (WARNING: cleancache_ops overridden)";
- pr_info("cleancache enabled, RAM provided by Xen Transcendent Memory%s\n",
- s);
+ int err;
+
+ err = cleancache_register_ops(&tmem_cleancache_ops);
+ if (err)
+ pr_warn("xen-tmem: failed to enable cleancache: %d\n",
+ err);
+ else
+ pr_info("cleancache enabled, RAM provided by "
+ "Xen Transcendent Memory\n");
}
#endif
#ifdef CONFIG_XEN_SELFBALLOONING
diff --git a/include/linux/cleancache.h b/include/linux/cleancache.h
index 29657d1c83fb..b23611f43cfb 100644
--- a/include/linux/cleancache.h
+++ b/include/linux/cleancache.h
@@ -33,8 +33,7 @@ struct cleancache_ops {
void (*invalidate_fs)(int);
};
-extern struct cleancache_ops *
- cleancache_register_ops(struct cleancache_ops *ops);
+extern int cleancache_register_ops(struct cleancache_ops *ops);
extern void __cleancache_init_fs(struct super_block *);
extern void __cleancache_init_shared_fs(struct super_block *);
extern int __cleancache_get_page(struct page *);
diff --git a/mm/cleancache.c b/mm/cleancache.c
index 532495f2e4f4..aa10f9a3bc88 100644
--- a/mm/cleancache.c
+++ b/mm/cleancache.c
@@ -106,15 +106,17 @@ static DEFINE_MUTEX(poolid_mutex);
*/
/*
- * Register operations for cleancache, returning previous thus allowing
- * detection of multiple backends and possible nesting.
+ * Register operations for cleancache. Returns 0 on success.
*/
-struct cleancache_ops *cleancache_register_ops(struct cleancache_ops *ops)
+int cleancache_register_ops(struct cleancache_ops *ops)
{
- struct cleancache_ops *old = cleancache_ops;
int i;
mutex_lock(&poolid_mutex);
+ if (cleancache_ops) {
+ mutex_unlock(&poolid_mutex);
+ return -EBUSY;
+ }
for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
if (fs_poolid_map[i] == FS_NO_BACKEND)
fs_poolid_map[i] = ops->init_fs(PAGE_SIZE);
@@ -130,7 +132,7 @@ struct cleancache_ops *cleancache_register_ops(struct cleancache_ops *ops)
barrier();
cleancache_ops = ops;
mutex_unlock(&poolid_mutex);
- return old;
+ return 0;
}
EXPORT_SYMBOL(cleancache_register_ops);