aufs: sbinfo list

When user accesses aufs via other than fs related systemcalls, aufs
needs to identify which superblock is the target.  Here is the trick.
It is just a list of aufs superblocks.  Such way will be procfs and
MagicSysRq key.  For MagicSysRq support, see the later commit.
This is a dirty approach which I don't like, but I just don't have
another idea.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

fs/aufs/Kconfig

@@ -44,6 +44,14 @@ config AUFS_BRANCH_MAX_32767
 	resources and has a minor impact to performance.
 endchoice
 
+config AUFS_SBILIST
+	bool
+	depends on PROC_FS
+	default y
+	help
+	Automatic configuration for internal use.
+	When aufs supports Magic SysRq or /proc, enabled automatically.
+
 config AUFS_DEBUG
 	bool "Debug aufs"
 	help

fs/aufs/module.c

@@ -103,6 +103,14 @@ static int __init au_cache_init(void)
 
 /* ---------------------------------------------------------------------- */
 
+#ifdef CONFIG_AUFS_SBILIST
+/*
+ * iterate_supers_type() doesn't protect us from
+ * remounting (branch management)
+ */
+struct hlist_bl_head au_sbilist;
+#endif
+
 /*
  * functions for module interface.
  */
@@ -151,6 +159,7 @@ static int __init aufs_init(void)
 
 	memset(au_cache, 0, sizeof(au_cache));
 
+	au_sbilist_init();
 	sysaufs_brs_init();
 	err = sysaufs_init();
 	if (unlikely(err))

fs/aufs/super.h

@@ -14,6 +14,7 @@
 
 #include <linux/fs.h>
 #include <linux/kobject.h>
+#include "hbl.h"
 #include "rwsem.h"
 #include "wkq.h"
 
@@ -66,6 +67,10 @@ struct au_sbinfo {
 	 */
 	struct kobject		si_kobj;
 
+#ifdef CONFIG_AUFS_SBILIST
+	struct hlist_bl_node	si_list;
+#endif
+
 	/* dirty, necessary for unmounting, sysfs and sysrq */
 	struct super_block	*si_sb;
 };
@@ -108,6 +113,35 @@ static inline struct au_sbinfo *au_sbi(struct super_block *sb)
 
 /* ---------------------------------------------------------------------- */
 
+#ifdef CONFIG_AUFS_SBILIST
+/* module.c */
+extern struct hlist_bl_head au_sbilist;
+
+static inline void au_sbilist_init(void)
+{
+	INIT_HLIST_BL_HEAD(&au_sbilist);
+}
+
+static inline void au_sbilist_add(struct super_block *sb)
+{
+	au_hbl_add(&au_sbi(sb)->si_list, &au_sbilist);
+}
+
+static inline void au_sbilist_del(struct super_block *sb)
+{
+	au_hbl_del(&au_sbi(sb)->si_list, &au_sbilist);
+}
+
+#define AuGFP_SBILIST	GFP_NOFS
+#else
+AuStubVoid(au_sbilist_init, void)
+AuStubVoid(au_sbilist_add, struct super_block *sb)
+AuStubVoid(au_sbilist_del, struct super_block *sb)
+#define AuGFP_SBILIST	GFP_NOFS
+#endif
+
+/* ---------------------------------------------------------------------- */
+
 /* lock superblock. mainly for entry point functions */
 #define __si_read_lock(sb)	au_rw_read_lock(&au_sbi(sb)->si_rwsem)
 #define __si_write_lock(sb)	au_rw_write_lock(&au_sbi(sb)->si_rwsem)