block/loop: handle discard/zeroout error

Fix some problems when setting up loop device with a block device as back file and create/mount ext4 in the loop device.

BTW: blkdev_issue_zeroout retries if we immediately find the device doesn't support zeroout, but it doesn't retry if submit_bio_wait returns -EOPNOTSUPP. Is this correct behavior?

Thanks,
Shaohua

Shaohua Li (3):
block/loop: don't hijack error number
block/loop: use FALLOC_FL_ZERO_RANGE for REQ_OP_WRITE_ZEROES block/loop: suppress discard IO error message

 drivers/block/loop.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

2.9.5

If the bio returns -EOPNOTSUPP, we shouldn't hijack it and return -EIO

---
 drivers/block/loop.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index ef83349..054dccc 100644
@@ -464,7 +464,7 @@ static void lo_complete_rq(struct request *rq)
 		zero_fill_bio(bio);
 	}
 
-	blk_mq_end_request(rq, cmd->ret < 0 ? BLK_STS_IOERR : BLK_STS_OK);
+	blk_mq_end_request(rq, errno_to_blk_status(cmd->ret));
 }
 
 static void lo_rw_aio_complete(struct kiocb *iocb, long ret, long ret2)

@@ -1725,7 +1725,7 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
  failed:
 	/* complete non-aio request */
 	if (!cmd->use_aio || ret) {
-		cmd->ret = ret ? -EIO : 0;
+		cmd->ret = ret;
 		blk_mq_complete_request(cmd->rq);
 	}
 }

2.9.5

REQ_OP_WRITE_ZEROES really means zero the data. And the in blkdev_fallocate, FALLOC_FL_ZERO_RANGE will retry but FALLOC_FL_PUNCH_HOLE not, even loop request doesn't have BLKDEV_ZERO_NOFALLBACK set.

---
 drivers/block/loop.c | 3 +++
 1 file changed, 3 insertions(+)

index 054dccc..a30aa45 100644
@@ -430,6 +430,9 @@ static int lo_discard(struct loop_device *lo, struct request *rq, loff_t pos)
 	int mode = FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE;
 	int ret;
 
+	if (req_op(rq) == REQ_OP_WRITE_ZEROES)
+		mode = FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE;
+
 	if ((!file->f_op->fallocate) || lo->lo_encrypt_key_size) {
 		ret = -EOPNOTSUPP;
 		goto out;

2.9.5

We don't know if fallocate really supports FALLOC_FL_PUNCH_HOLE till fallocate is called. If it doesn't support, loop will return -EOPNOTSUPP and we seee a lot of error message printed by blk_update_request. Failure for discard IO isn't a problem, so we just return 0 in loop which will suppress the IO error message

---
 drivers/block/loop.c | 3 +++
 1 file changed, 3 insertions(+)

index a30aa45..15f51e3 100644
@@ -441,6 +441,9 @@ static int lo_discard(struct loop_device *lo, struct request *rq, loff_t pos)
 	ret = file->f_op->fallocate(file, mode, pos, blk_rq_bytes(rq));
 	if (unlikely(ret && ret != -EINVAL && ret != -EOPNOTSUPP))
 		ret = -EIO;
+
+	if (req_op(rq) == REQ_OP_DISCARD && ret == -EOPNOTSUPP)
+		ret = 0;
  out:
 	return ret;
 }

2.9.5