dm thin: provide specific errors for two table load failure cases

Provide specific error message strings for two pool_ctr() failure cases
that currently give just "Unknown error".

Reference: test_two_pools_pointing_to_the_same_metadata_fails and
test_different_pool_cant_replace_pool in thinp-test-suite.

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

1 files changed, 6 insertions, 2 deletions

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 0bb9e646e215..e89f8e7d8a33 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1828,15 +1828,19 @@ static struct pool *__pool_find(struct mapped_device *pool_md,
         struct pool *pool = __pool_table_lookup_metadata_dev(metadata_dev);
 
         if (pool) {
-                if (pool->pool_md != pool_md)
+                if (pool->pool_md != pool_md) {
+                        *error = "metadata device already in use by a pool";
                         return ERR_PTR(-EBUSY);
+                }
                 __pool_inc(pool);
 
         } else {
                 pool = __pool_table_lookup(pool_md);
                 if (pool) {
-                        if (pool->md_dev != metadata_dev)
+                        if (pool->md_dev != metadata_dev) {
+                                *error = "different pool cannot replace a pool";
                                 return ERR_PTR(-EINVAL);
+                        }
                         __pool_inc(pool);
 
                 } else {