ext4: stop issuing discards if not supported by device

Turn off issuance of discard requests if the device does
not support it - similar to the action we take for barriers.
This will save a little computation time if a non-discardable
device is mounted with -o discard, and also makes it obvious
that it's not doing what was asked at mount time ...

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 8639d5a637b25ac790bf368f2490af115c7b67fe..4f2d3a9d4e21c493eb2d8b142733f6e3159acbc1 100644 (file)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2534,6 +2534,7 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
                         entry->count, entry->group, entry);
 
                if (test_opt(sb, DISCARD)) {
+                       int ret;
                        ext4_fsblk_t discard_block;
 
                        discard_block = entry->start_blk +
@@ -2541,7 +2542,12 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
                        trace_ext4_discard_blocks(sb,
                                        (unsigned long long)discard_block,
                                        entry->count);
-                       sb_issue_discard(sb, discard_block, entry->count);
+                       ret = sb_issue_discard(sb, discard_block, entry->count);
+                       if (ret == EOPNOTSUPP) {
+                               ext4_warning(sb,
+                                       "discard not supported, disabling");
+                               clear_opt(EXT4_SB(sb)->s_mount_opt, DISCARD);
+                       }
                }
 
                err = ext4_mb_load_buddy(sb, entry->group, &e4b);