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>

1 files changed, 7 insertions, 1 deletions

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 8639d5a637b2..4f2d3a9d4e21 100644
--- 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);