Add sysfs routine sysfs_ns_exit() to allow a namespace to go away while
sysfs is still mounted. 

The exiting namespace calls this routine and pass it a callback to be 
called for every sysfs superblocks present. The callback contains the 
necessary code to clean the superblock tag data associated with this 
namespace.

Signed-off-by: Benjamin Thery <benjamin.thery@bull.net>
---
 fs/sysfs/mount.c      |   21 +++++++++++++++++++++
 include/linux/sysfs.h |    8 ++++++++
 2 files changed, 29 insertions(+)

Index: linux-mm/fs/sysfs/mount.c
===================================================================
--- linux-mm.orig/fs/sysfs/mount.c
+++ linux-mm/fs/sysfs/mount.c
@@ -181,6 +181,27 @@ restart:
 	spin_unlock(&sb_lock);
 }
 
+/* Clean sysfs tags related to a given namespace when it exits */
+void sysfs_ns_exit(void (*func)(struct sysfs_tag_info *, void *), void *data)
+{
+	/* Allow the namespace to go away while sysfs is still mounted. */
+	struct super_block *sb;
+	mutex_lock(&sysfs_rename_mutex);
+	sysfs_grab_supers();
+	mutex_lock(&sysfs_mutex);
+	list_for_each_entry(sb, &sysfs_fs_type.fs_supers, s_instances) {
+
+		struct sysfs_super_info *info = sysfs_info(sb);
+		/* Call the cleaning routine provided by the namespace.
+		 * data is the current namespace id passed by the namespace.
+		 */
+		func(&info->tag, data);
+	}
+	mutex_unlock(&sysfs_mutex);
+	sysfs_release_supers();
+	mutex_unlock(&sysfs_rename_mutex);
+}
+
 int __init sysfs_init(void)
 {
 	int err = -ENOMEM;
Index: linux-mm/include/linux/sysfs.h
===================================================================
--- linux-mm.orig/include/linux/sysfs.h
+++ linux-mm/include/linux/sysfs.h
@@ -134,6 +134,9 @@ void sysfs_printk_last_file(void);
 int sysfs_enable_tagging(struct kobject *kobj,
 			 const struct sysfs_tagged_dir_operations *tag_ops);
 
+void sysfs_ns_exit(void (*func)(struct sysfs_tag_info *, void *),
+		   void *data);
+
 extern int __must_check sysfs_init(void);
 
 #else /* CONFIG_SYSFS */
@@ -247,6 +250,11 @@ static inline int sysfs_enable_tagging(s
 	return 0;
 }
 
+static inline void sysfs_ns_exit(void (*func)(struct sysfs_tag_info *, void *),
+				 void *data)
+{
+}
+
 static inline int __must_check sysfs_init(void)
 {
 	return 0;

-- 
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