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/super.c b/fs/ubifs/super.c
index 372c7fb..302a205 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -1351,8 +1351,9 @@
x = (long long)c->log_lebs * c->leb_size + c->max_bud_bytes;
ubifs_msg("journal size: %lld bytes (%lld KiB, %lld MiB, %d "
"LEBs)", x, x >> 10, x >> 20, c->log_lebs + c->max_bud_cnt);
- ubifs_msg("media format: %d (latest is %d)",
- c->fmt_version, UBIFS_FORMAT_VERSION);
+ ubifs_msg("media format: w%d/r%d (latest is w%d/r%d)",
+ c->fmt_version, c->ro_compat_version,
+ UBIFS_FORMAT_VERSION, UBIFS_RO_COMPAT_VERSION);
ubifs_msg("default compressor: %s", ubifs_compr_name(c->default_compr));
ubifs_msg("reserved for root: %llu bytes (%llu KiB)",
c->report_rp_size, c->report_rp_size >> 10);
@@ -1492,6 +1493,15 @@
{
int err, lnum;
+ if (c->rw_incompat) {
+ ubifs_err("the file-system is not R/W-compatible");
+ ubifs_msg("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);
+ return -EROFS;
+ }
+
mutex_lock(&c->umount_mutex);
dbg_save_space_info(c);
c->remounting_rw = 1;