There are sysfs interfaces in some fs, only btrfs yet, which will modify
on-disk data.
Unlike normal file operation routine we can use mnt_want_write_file() to
protect the operation, change through sysfs won't to be binded to any file
in the filesystem.
So introduce new sb_want_write() to do the protection agains a super
block, which acts much like mnt_want_write() but will return success if
the super block is read-write.
Cc: linux-fsdevel <linux-fsdevel@xxxxxxxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
---
Changelog:
v4:
Newly introduced.
v5:
Change name to sb_want_write() and receive sb and parameter.
---
fs/namespace.c | 36 ++++++++++++++++++++++++++++++++++++
include/linux/mount.h | 2 ++
2 files changed, 38 insertions(+)
diff --git a/fs/namespace.c b/fs/namespace.c
index cd1e968..79bc762 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1105,6 +1105,42 @@ struct vfsmount *mntget(struct vfsmount *mnt)
}
EXPORT_SYMBOL(mntget);
+/**
+ * sb_want_write - get write acess to a super block
+ * @sb: the superblock of the filesystem
+ *
+ * This tells the low-level filesystem that a write is about to be performed to
+ * it, and makes sure that the writes are allowed (superblock is read-write,
+ * filesystem is not frozen) before returning success.
+ * When the write operation is finished, sb_drop_write() must be called.
+ * This is much like mnt_want_write() as a refcount, but only needs
+ * the superblock to be read-write.
+ */
+int sb_want_write(struct super_block *sb)
+{
+ sb_start_write(sb);
+ if (sb->s_readonly_remount || sb->s_flags & MS_RDONLY) {
+ sb_end_write(sb);
+ return -EROFS;
+ }
+ return 0;
+}
+EXPORT_SYMBOL(sb_want_write);
+
+/**
+ * sb_drop_write - give up write acess to a super block
+ * @sb: the superblock on which to give up write access
+ *
+ * Tells the low-level filesystem that we are done performing writes to it and
+ * also allows filesystem to be frozen again. Must be matched with
+ * sb_want_write() call above.
+ */
+void sb_drop_write(struct super_block *sb)
+{
+ sb_end_write(sb);
+}
+EXPORT_SYMBOL(sb_drop_write);
+
struct vfsmount *mnt_clone_internal(struct path *path)
{
struct mount *p;
diff --git a/include/linux/mount.h b/include/linux/mount.h
index c2c561d..abf4495 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -74,8 +74,10 @@ struct path;
extern int mnt_want_write(struct vfsmount *mnt);
extern int mnt_want_write_file(struct file *file);
extern int mnt_clone_write(struct vfsmount *mnt);
+extern int sb_want_write(struct super_block *sb);
extern void mnt_drop_write(struct vfsmount *mnt);
extern void mnt_drop_write_file(struct file *file);
+extern void sb_drop_write(struct super_block *sb);
extern void mntput(struct vfsmount *mnt);
extern struct vfsmount *mntget(struct vfsmount *mnt);
extern struct vfsmount *mnt_clone_internal(struct path *path);
--
2.2.2
--
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