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>
Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/fs/ubifs/sb.c b/fs/ubifs/sb.c
index 9708fda..00c9cd3 100644
--- a/fs/ubifs/sb.c
+++ b/fs/ubifs/sb.c
@@ -235,17 +235,39 @@
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) {
diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index 95f2a41..391dea4 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -727,8 +727,9 @@
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);
@@ -967,6 +968,15 @@
if (c->max_inode_sz > MAX_LFS_FILESIZE)
sb->s_maxbytes = c->max_inode_sz = MAX_LFS_FILESIZE;
+ 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);
err = mount_ubifs(c);
if (err) {
diff --git a/fs/ubifs/ubifs-media.h b/fs/ubifs/ubifs-media.h
index b25fc36..3eee07e 100644
--- a/fs/ubifs/ubifs-media.h
+++ b/fs/ubifs/ubifs-media.h
@@ -36,9 +36,31 @@
/* UBIFS node magic number (must not have the padding byte first or last) */
#define UBIFS_NODE_MAGIC 0x06101831
-/* UBIFS on-flash format version */
+/*
+ * UBIFS on-flash format version. This version is increased when the on-flash
+ * format is changing. If this happens, UBIFS is will support older versions as
+ * well. But older UBIFS code will not support newer formats. Format changes
+ * will be rare and only when absolutely necessary, e.g. to fix a bug or to add
+ * a new feature.
+ *
+ * UBIFS went into mainline kernel with format version 4. The older formats
+ * were development formats.
+ */
#define UBIFS_FORMAT_VERSION 4
+/*
+ * Read-only compatibility version. If the UBIFS format is changed, older UBIFS
+ * implementations will not be able to mount newer formats in read-write mode.
+ * However, depending on the change, it may be possible to mount newer formats
+ * in R/O mode. This is indicated by the R/O compatibility version which is
+ * stored in the super-block.
+ *
+ * This is needed to support boot-loaders which only need R/O mounting. With
+ * this flag it is possible to do UBIFS format changes without a need to update
+ * boot-loaders.
+ */
+#define UBIFS_RO_COMPAT_VERSION 0
+
/* Minimum logical eraseblock size in bytes */
#define UBIFS_MIN_LEB_SZ (15*1024)
@@ -53,7 +75,7 @@
/*
* If compressed data length is less than %UBIFS_MIN_COMPRESS_DIFF bytes
- * shorter than uncompressed data length, UBIFS preferes to leave this data
+ * shorter than uncompressed data length, UBIFS prefers to leave this data
* node uncompress, because it'll be read faster.
*/
#define UBIFS_MIN_COMPRESS_DIFF 64
@@ -586,6 +608,7 @@
* @padding2: reserved for future, zeroes
* @time_gran: time granularity in nanoseconds
* @uuid: UUID generated when the file system image was created
+ * @ro_compat_version: UBIFS R/O compatibility version
*/
struct ubifs_sb_node {
struct ubifs_ch ch;
@@ -612,7 +635,8 @@
__le64 rp_size;
__le32 time_gran;
__u8 uuid[16];
- __u8 padding2[3972];
+ __le32 ro_compat_version;
+ __u8 padding2[3968];
} __attribute__ ((packed));
/**
diff --git a/fs/ubifs/ubifs.h b/fs/ubifs/ubifs.h
index f342dd8..91351de 100644
--- a/fs/ubifs/ubifs.h
+++ b/fs/ubifs/ubifs.h
@@ -1386,6 +1386,7 @@
* by @commit_sem
* @cnt_lock: protects @highest_inum and @max_sqnum counters
* @fmt_version: UBIFS on-flash format version
+ * @ro_compat_version: R/O compatibility version
* @uuid: UUID from super block
*
* @lhead_lnum: log head logical eraseblock number
@@ -1418,6 +1419,7 @@
* recovery)
* @bulk_read: enable bulk-reads
* @default_compr: default compression algorithm (%UBIFS_COMPR_LZO, etc)
+ * @rw_incompat: the media is not R/W compatible
*
* @tnc_mutex: protects the Tree Node Cache (TNC), @zroot, @cnext, @enext, and
* @calc_idx_sz
@@ -1628,6 +1630,7 @@
unsigned long long cmt_no;
spinlock_t cnt_lock;
int fmt_version;
+ int ro_compat_version;
unsigned char uuid[16];
int lhead_lnum;
@@ -1656,6 +1659,7 @@
unsigned int no_chk_data_crc:1;
unsigned int bulk_read:1;
unsigned int default_compr:2;
+ unsigned int rw_incompat:1;
struct mutex tnc_mutex;
struct ubifs_zbranch zroot;