dm thin metadata: introduce dm_pool_metadata_set_read_only

Introduce dm_pool_metadata_set_read_only to put the underlying block
manager into read-only mode.

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

2 files changed, 22 insertions, 4 deletions

diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c
index 4f5b11c195f..d30bc09fd7c 100644
--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -184,6 +184,7 @@ struct dm_pool_metadata {
         uint64_t trans_id;
         unsigned long flags;
         sector_t data_block_size;
+        bool read_only:1;
 };
 
 struct dm_thin_device {
@@ -807,6 +808,7 @@ struct dm_pool_metadata *dm_pool_metadata_open(struct block_device *bdev,
         init_rwsem(&pmd->root_lock);
         pmd->time = 0;
         INIT_LIST_HEAD(&pmd->thin_devices);
+        pmd->read_only = false;
         pmd->bdev = bdev;
         pmd->data_block_size = data_block_size;
 
@@ -849,10 +851,12 @@ int dm_pool_metadata_close(struct dm_pool_metadata *pmd)
                 return -EBUSY;
         }
 
-        r = __commit_transaction(pmd);
-        if (r < 0)
-                DMWARN("%s: __commit_transaction() failed, error = %d",
-                       __func__, r);
+        if (!pmd->read_only) {
+                r = __commit_transaction(pmd);
+                if (r < 0)
+                        DMWARN("%s: __commit_transaction() failed, error = %d",
+                               __func__, r);
+        }
 
         __destroy_persistent_data_objects(pmd);
         kfree(pmd);
@@ -1587,3 +1591,11 @@ int dm_pool_resize_data_dev(struct dm_pool_metadata *pmd, dm_block_t new_count)
 
         return r;
 }
+
+void dm_pool_metadata_read_only(struct dm_pool_metadata *pmd)
+{
+        down_write(&pmd->root_lock);
+        pmd->read_only = true;
+        dm_bm_set_read_only(pmd->bm);
+        up_write(&pmd->root_lock);
+}
diff --git a/drivers/md/dm-thin-metadata.h b/drivers/md/dm-thin-metadata.h
index 1632fec1660..2bbe622f299 100644
--- a/drivers/md/dm-thin-metadata.h
+++ b/drivers/md/dm-thin-metadata.h
@@ -174,6 +174,12 @@ int dm_pool_get_data_dev_size(struct dm_pool_metadata *pmd, dm_block_t *result);
  */
 int dm_pool_resize_data_dev(struct dm_pool_metadata *pmd, dm_block_t new_size);
 
+/*
+ * Flicks the underlying block manager into read only mode, so you know
+ * that nothing is changing.
+ */
+void dm_pool_metadata_read_only(struct dm_pool_metadata *pmd);
+
 /*----------------------------------------------------------------*/
 
 #endif