Improve table versioning.

[osl.git] / osl.c

diff --git a/osl.c b/osl.c
index 430d120fb3a286f61e1eb2a8ab3c2912d6652206..90601dc287e3b8ec3de7baf7b9d1c6f2862e1c72 100644 (file)
--- a/osl.c
+++ b/osl.c
@@ -341,7 +341,7 @@ err:
 int read_table_desc(struct osl_object *map, struct osl_table_description *desc)
 {
        char *buf = map->data;
-       uint8_t version;
+       uint8_t version, compat_version, create_version;
        uint16_t header_size;
        int ret, i;
        unsigned offset;
@@ -352,7 +352,19 @@ int read_table_desc(struct osl_object *map, struct osl_table_description *desc)
        if (strncmp(buf + IDX_OSL_MAGIC, OSL_MAGIC, strlen(OSL_MAGIC)))
                return -E_OSL_NO_MAGIC;
        version = read_u8(buf + IDX_VERSION);
-       if (version < MIN_TABLE_VERSION || version > MAX_TABLE_VERSION)
+       /*
+        * The on-disk version consists of two version numbers: the
+        * create_version (low 4 bits) is the CURRENT_TABLE_VERSION version
+        * number of the library that created the table, and compat_version
+        * (high 4 bits) tells us the lowest version of the library that can
+        * still read this table.
+        */
+       create_version = version & 0xf;
+       compat_version = version >> 4;
+       INFO_LOG("create_version: %u, compat_version: %u\n", create_version,
+               compat_version);
+       if (create_version < MIN_TABLE_VERSION /* table too old */
+               || compat_version > CURRENT_TABLE_VERSION) /* libosl too old */
                return -E_OSL_VERSION_MISMATCH;
        desc->flags = read_u8(buf + IDX_TABLE_FLAGS);
        desc->num_columns = read_u16(buf + IDX_NUM_COLUMNS);
@@ -487,7 +499,8 @@ static int create_table_index(struct osl_table *t)
        sprintf(buf + IDX_OSL_MAGIC, "%s", OSL_MAGIC);
        write_u8(buf + IDX_TABLE_FLAGS, t->desc->flags);
        write_u8(buf + IDX_DIRTY_FLAG, 0);
-       write_u8(buf + IDX_VERSION, CURRENT_TABLE_VERSION);
+       write_u8(buf + IDX_VERSION, CURRENT_TABLE_VERSION
+               + (COMPAT_TABLE_VERSION << 4));
        write_u16(buf + IDX_NUM_COLUMNS, t->num_mapped_columns + t->num_disk_storage_columns);
        write_u16(buf + IDX_HEADER_SIZE, t->index_header_size);
        offset = IDX_COLUMN_DESCRIPTIONS;