[RFC 1/2] FS: mount_bdev from vfs instead of filesystem specific mount function.

[RFC 1/2] FS: mount_bdev from vfs instead of filesystem specific mount function.

[Fabian Frederick]

Currently, a lot of filesystem mounting functions feature in
file_system_type only to be called from vfs mount_fs and call mount_bdev.

This patch adds fill_super function to that structure and lets vfs
call mount_bdev when no mount function is declared.

Signed-off-by: Fabian Frederick <fabf@skynet.be>
---
 fs/super.c         | 6 +++++-
 include/linux/fs.h | 2 ++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/super.c b/fs/super.c
index a89d625..7c37355 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1112,7 +1112,11 @@ mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
 			goto out_free_secdata;
 	}
 
-	root = type->mount(type, flags, name, data);
+	if (type->mount)
+		root = type->mount(type, flags, name, data);
+	else
+		root = mount_bdev(type, flags, name, data, type->fill_super);
+
 	if (IS_ERR(root)) {
 		error = PTR_ERR(root);
 		goto out_free_secdata;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0bd9669..3e19349 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1846,8 +1846,10 @@ struct file_system_type {
 #define FS_USERNS_MOUNT		8	/* Can be mounted by userns root */
 #define FS_USERNS_DEV_MOUNT	16 /* A userns mount does not imply MNT_NODEV */
 #define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move() during rename() internally. */
+	int (*fill_super)(struct super_block *, void *, int);
 	struct dentry *(*mount) (struct file_system_type *, int,
 		       const char *, void *);
+
 	void (*kill_sb) (struct super_block *);
 	struct module *owner;
 	struct file_system_type * next;
-- 
1.9.3

Re: [RFC 1/2] FS: mount_bdev from vfs instead of filesystem specific mount function.

[Al Viro]

On Mon, Jan 19, 2015 at 09:47:20PM +0100, Fabian Frederick wrote:
> Currently, a lot of filesystem mounting functions feature in
> file_system_type only to be called from vfs mount_fs and call mount_bdev.
> 
> This patch adds fill_super function to that structure and lets vfs
> call mount_bdev when no mount function is declared.

NAK.  First of all, quite a few of them are _not_ mount_bdev() users.
What's more, you are trading about 4 lines per filesystem (two of them
being { and }) for a layering violation.

No point whatsoever.  fill_super() is no more a method than e.g. get_block().