/* 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)
*/
#define UBIFS_MIN_COMPR_LEN 128
+/*
+ * If compressed data length is less than %UBIFS_MIN_COMPRESS_DIFF bytes
+ * 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
+
/* Root inode number */
#define UBIFS_ROOT_INO 1
*/
#define UBIFS_BLOCK_SIZE 4096
#define UBIFS_BLOCK_SHIFT 12
-#define UBIFS_BLOCK_MASK 0x00000FFF
/* UBIFS padding byte pattern (must not be first or last byte of node magic) */
#define UBIFS_PADDING_BYTE 0xCE
#define UBIFS_SK_LEN 8
/* Minimum index tree fanout */
-#define UBIFS_MIN_FANOUT 2
+#define UBIFS_MIN_FANOUT 3
/* Maximum number of levels in UBIFS indexing B-tree */
#define UBIFS_MAX_LEVELS 512
/* Minimum number of orphan area logical eraseblocks */
#define UBIFS_MIN_ORPH_LEBS 1
/*
- * Minimum number of main area logical eraseblocks (buds, 2 for the index, 1
+ * Minimum number of main area logical eraseblocks (buds, 3 for the index, 1
* for GC, 1 for deletions, and at least 1 for committed data).
*/
-#define UBIFS_MIN_MAIN_LEBS (UBIFS_MIN_BUD_LEBS + 5)
+#define UBIFS_MIN_MAIN_LEBS (UBIFS_MIN_BUD_LEBS + 6)
/* Minimum number of logical eraseblocks */
#define UBIFS_MIN_LEB_CNT (UBIFS_SB_LEBS + UBIFS_MST_LEBS + \
* @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;
__le64 rp_size;
__le32 time_gran;
__u8 uuid[16];
- __u8 padding2[3972];
+ __le32 ro_compat_version;
+ __u8 padding2[3968];
} __attribute__ ((packed));
/**