UBIFS: introduce new flags for RO mounts

Commit 2fde99cb55fb9d9b88180512a5e8a5d939d27fec "UBIFS: mark VFS SB RO too"
introduced regression. This commit made UBIFS set the 'MS_RDONLY' flag in the
VFS superblock when it switches to R/O mode due to an error. This was done
to make VFS show the R/O UBIFS flag in /proc/mounts.

However, several places in UBIFS relied on the 'MS_RDONLY' flag and assume this
flag can only change when we re-mount. For example, 'ubifs_put_super()'.

This patch introduces new UBIFS flag - 'c->ro_mount' which changes only when
we re-mount, and preserves the way UBIFS was originally mounted (R/W or R/O).
This allows us to de-initialize UBIFS cleanly in 'ubifs_put_super()'.

This patch also changes all 'ubifs_assert(!c->ro_media)' assertions to
'ubifs_assert(!c->ro_media && !c->ro_mount)', because we never should write
anything if the FS was mounter R/O.

All the places where we test for 'MS_RDONLY' flag in the VFS SB were changed
and now we test the 'c->ro_mount' flag instead, because it preserves the
original UBIFS mount type, unlike the 'MS_RDONLY' flag.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

1 files changed, 3 insertions, 6 deletions

diff --git a/fs/ubifs/sb.c b/fs/ubifs/sb.c
index 96cb62c8a9dd..bf31b4729e51 100644
--- a/fs/ubifs/sb.c
+++ b/fs/ubifs/sb.c
@@ -542,11 +542,8 @@ int ubifs_read_superblock(struct ubifs_info *c)
          * due to the unavailability of time-travelling equipment.
          */
         if (c->fmt_version > UBIFS_FORMAT_VERSION) {
-                struct super_block *sb = c->vfs_sb;
-                int mounting_ro = sb->s_flags & MS_RDONLY;
-
-                ubifs_assert(!c->ro_media || mounting_ro);
-                if (!mounting_ro ||
+                ubifs_assert(!c->ro_media || c->ro_mount);
+                if (!c->ro_mount ||
                     c->ro_compat_version > UBIFS_RO_COMPAT_VERSION) {
                         ubifs_err("on-flash format version is w%d/r%d, but "
                                   "software only supports up to version "
@@ -624,7 +621,7 @@ int ubifs_read_superblock(struct ubifs_info *c)
         c->old_leb_cnt = c->leb_cnt;
         if (c->leb_cnt < c->vi.size && c->leb_cnt < c->max_leb_cnt) {
                 c->leb_cnt = min_t(int, c->max_leb_cnt, c->vi.size);
-                if (c->vfs_sb->s_flags & MS_RDONLY)
+                if (c->ro_mount)
                         dbg_mnt("Auto resizing (ro) from %d LEBs to %d LEBs",
                                 c->old_leb_cnt, c->leb_cnt);
                 else {