[PATCH v3] ubifs: allow userspace to map mounts to volumes

[Rabin Vincent]

There currently appears to be no way for userspace to find out the
underlying volume number for a mounted ubifs file system, since ubifs
uses anonymous block devices.  The volume name is present in
/proc/mounts but UBI volumes can be renamed after the volume has been
mounted.

To remedy this, show the UBI number and UBI volume number as part of the
options visible under /proc/mounts.

 # mount -t ubifs ubi:baz x
 # mount
 ubi:baz on /root/x type ubifs (rw,relatime,ubi=0,vol=2)
 # ubirename /dev/ubi0 baz bazz
 # mount
 ubi:baz on /root/x type ubifs (rw,relatime,ubi=0,vol=2)
 # ubinfo -d 0 -n 2
 Volume ID:   2 (on ubi0)
 Type:        dynamic
 Alignment:   1
 Size:        67 LEBs (1063424 bytes, 1.0 MiB)
 State:       OK
 Name:        bazz
 Character device major/minor: 254:3

Signed-off-by: Rabin Vincent <rabinv@xxxxxxxx>
---
 fs/ubifs/super.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index cf4cc99..4b54186 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -446,6 +446,8 @@ static int ubifs_show_options(struct seq_file *s, struct dentry *root)
 			   ubifs_compr_name(c->mount_opts.compr_type));
 	}
 
+	seq_printf(s, ",ubi=%d,vol=%d", c->vi.ubi_num, c->vi.vol_id);
+
 	return 0;
 }
 
-- 
2.1.4