dm cache: policy change version from string to integer set

Separate dm cache policy version string into 3 unsigned numbers
corresponding to major, minor and patchlevel and store them at the end
of the on-disk metadata so we know which version of the policy generated
the hints in case a future version wants to use them differently.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 13 insertions, 2 deletions

diff --git a/drivers/md/dm-cache-metadata.c b/drivers/md/dm-cache-metadata.c
index 1bb91802b22a..74213d1f1db5 100644
--- a/drivers/md/dm-cache-metadata.c
+++ b/drivers/md/dm-cache-metadata.c
@@ -83,6 +83,8 @@ struct cache_disk_superblock {
         __le32 read_misses;
         __le32 write_hits;
         __le32 write_misses;
+
+        __le32 policy_version[CACHE_POLICY_VERSION_SIZE];
 } __packed;
 
 struct dm_cache_metadata {
@@ -109,6 +111,7 @@ struct dm_cache_metadata {
         bool clean_when_opened:1;
 
         char policy_name[CACHE_POLICY_NAME_SIZE];
+        unsigned policy_version[CACHE_POLICY_VERSION_SIZE];
         size_t policy_hint_size;
         struct dm_cache_statistics stats;
 };
@@ -268,7 +271,8 @@ static int __write_initial_superblock(struct dm_cache_metadata *cmd)
         memset(disk_super->uuid, 0, sizeof(disk_super->uuid));
         disk_super->magic = cpu_to_le64(CACHE_SUPERBLOCK_MAGIC);
         disk_super->version = cpu_to_le32(CACHE_VERSION);
-        memset(disk_super->policy_name, 0, CACHE_POLICY_NAME_SIZE);
+        memset(disk_super->policy_name, 0, sizeof(disk_super->policy_name));
+        memset(disk_super->policy_version, 0, sizeof(disk_super->policy_version));
         disk_super->policy_hint_size = 0;
 
         r = dm_sm_copy_root(cmd->metadata_sm, &disk_super->metadata_space_map_root,
@@ -284,7 +288,6 @@ static int __write_initial_superblock(struct dm_cache_metadata *cmd)
         disk_super->metadata_block_size = cpu_to_le32(DM_CACHE_METADATA_BLOCK_SIZE >> SECTOR_SHIFT);
         disk_super->data_block_size = cpu_to_le32(cmd->data_block_size);
         disk_super->cache_blocks = cpu_to_le32(0);
-        memset(disk_super->policy_name, 0, sizeof(disk_super->policy_name));
 
         disk_super->read_hits = cpu_to_le32(0);
         disk_super->read_misses = cpu_to_le32(0);
@@ -478,6 +481,9 @@ static void read_superblock_fields(struct dm_cache_metadata *cmd,
         cmd->data_block_size = le32_to_cpu(disk_super->data_block_size);
         cmd->cache_blocks = to_cblock(le32_to_cpu(disk_super->cache_blocks));
         strncpy(cmd->policy_name, disk_super->policy_name, sizeof(cmd->policy_name));
+        cmd->policy_version[0] = le32_to_cpu(disk_super->policy_version[0]);
+        cmd->policy_version[1] = le32_to_cpu(disk_super->policy_version[1]);
+        cmd->policy_version[2] = le32_to_cpu(disk_super->policy_version[2]);
         cmd->policy_hint_size = le32_to_cpu(disk_super->policy_hint_size);
 
         cmd->stats.read_hits = le32_to_cpu(disk_super->read_hits);
@@ -572,6 +578,9 @@ static int __commit_transaction(struct dm_cache_metadata *cmd,
         disk_super->discard_nr_blocks = cpu_to_le64(from_dblock(cmd->discard_nr_blocks));
         disk_super->cache_blocks = cpu_to_le32(from_cblock(cmd->cache_blocks));
         strncpy(disk_super->policy_name, cmd->policy_name, sizeof(disk_super->policy_name));
+        disk_super->policy_version[0] = cpu_to_le32(cmd->policy_version[0]);
+        disk_super->policy_version[1] = cpu_to_le32(cmd->policy_version[1]);
+        disk_super->policy_version[2] = cpu_to_le32(cmd->policy_version[2]);
 
         disk_super->read_hits = cpu_to_le32(cmd->stats.read_hits);
         disk_super->read_misses = cpu_to_le32(cmd->stats.read_misses);
@@ -1070,6 +1079,7 @@ static int begin_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *po
         __le32 value;
         size_t hint_size;
         const char *policy_name = dm_cache_policy_get_name(policy);
+        const unsigned *policy_version = dm_cache_policy_get_version(policy);
 
         if (!policy_name[0] ||
             (strlen(policy_name) > sizeof(cmd->policy_name) - 1))
@@ -1077,6 +1087,7 @@ static int begin_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *po
 
         if (strcmp(cmd->policy_name, policy_name)) {
                 strncpy(cmd->policy_name, policy_name, sizeof(cmd->policy_name));
+                memcpy(cmd->policy_version, policy_version, sizeof(cmd->policy_version));
 
                 hint_size = dm_cache_policy_get_hint_size(policy);
                 if (!hint_size)