UBIFS: add R/O compatibility
Now UBIFS is supported by u-boot. If we ever decide to change the
media format, then people will have to upgrade their u-boots to
mount new format images. However, very often it is possible to
preserve R/O forward-compatibility, even though the write
forward-compatibility is not preserved.
This patch introduces a new super-block field which stores the
R/O compatibility version.
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Acked-by: Adrian Hunter <Adrian.Hunter@nokia.com>
diff --git a/fs/ubifs/sb.c b/fs/ubifs/sb.c
index 0dec47c..57085e4 100644
--- a/fs/ubifs/sb.c
+++ b/fs/ubifs/sb.c
@@ -193,6 +193,7 @@
if (tmp64 > DEFAULT_MAX_RP_SIZE)
tmp64 = DEFAULT_MAX_RP_SIZE;
sup->rp_size = cpu_to_le64(tmp64);
+ sup->ro_compat_version = cpu_to_le32(UBIFS_RO_COMPAT_VERSION);
err = ubifs_write_node(c, sup, UBIFS_SB_NODE_SZ, 0, 0, UBI_LONGTERM);
kfree(sup);
@@ -532,17 +533,39 @@
if (IS_ERR(sup))
return PTR_ERR(sup);
+ c->fmt_version = le32_to_cpu(sup->fmt_version);
+ c->ro_compat_version = le32_to_cpu(sup->ro_compat_version);
+
/*
* The software supports all previous versions but not future versions,
* due to the unavailability of time-travelling equipment.
*/
- c->fmt_version = le32_to_cpu(sup->fmt_version);
if (c->fmt_version > UBIFS_FORMAT_VERSION) {
- ubifs_err("on-flash format version is %d, but software only "
- "supports up to version %d", c->fmt_version,
- UBIFS_FORMAT_VERSION);
- err = -EINVAL;
- goto out;
+ 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 ||
+ 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 "
+ "w%d/r%d", c->fmt_version,
+ c->ro_compat_version, UBIFS_FORMAT_VERSION,
+ UBIFS_RO_COMPAT_VERSION);
+ if (c->ro_compat_version <= UBIFS_RO_COMPAT_VERSION) {
+ ubifs_msg("only R/O mounting is possible");
+ err = -EROFS;
+ } else
+ err = -EINVAL;
+ goto out;
+ }
+
+ /*
+ * The FS is mounted R/O, and the media format is
+ * R/O-compatible with the UBIFS implementation, so we can
+ * mount.
+ */
+ c->rw_incompat = 1;
}
if (c->fmt_version < 3) {