[dm-devel] [PATCH 09/23] loop: zero-fill bio on the submitting cpu

[Christoph Hellwig]

In thruth I've just audited which blk-mq drivers don't currently have a
complete callback, but I think this change is at least borderline useful.

Signed-off-by: Christoph Hellwig <h...@lst.de>
Reviewed-by: Ming Lei <ming....@redhat.com>
---
 drivers/block/loop.c | 30 ++++++++++++++----------------
 drivers/block/loop.h |  1 +
 2 files changed, 15 insertions(+), 16 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 3081d83d2ea3..86351b3f7350 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -445,32 +445,27 @@ static int lo_req_flush(struct loop_device *lo, struct 
request *rq)
        return ret;
 }
 
-static inline void handle_partial_read(struct loop_cmd *cmd, long bytes)
+static void lo_complete_rq(struct request *rq)
 {
-       if (bytes < 0 || op_is_write(req_op(cmd->rq)))
-               return;
+       struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq);
 
-       if (unlikely(bytes < blk_rq_bytes(cmd->rq))) {
+       if (unlikely(req_op(cmd->rq) == REQ_OP_READ && cmd->use_aio &&
+                    cmd->ret >= 0 && cmd->ret < blk_rq_bytes(cmd->rq))) {
                struct bio *bio = cmd->rq->bio;
 
-               bio_advance(bio, bytes);
+               bio_advance(bio, cmd->ret);
                zero_fill_bio(bio);
        }
+
+       blk_mq_end_request(rq, cmd->ret < 0 ? -EIO : 0);
 }
 
 static void lo_rw_aio_complete(struct kiocb *iocb, long ret, long ret2)
 {
        struct loop_cmd *cmd = container_of(iocb, struct loop_cmd, iocb);
-       struct request *rq = cmd->rq;
-
-       handle_partial_read(cmd, ret);
 
-       if (ret > 0)
-               ret = 0;
-       else if (ret < 0)
-               ret = -EIO;
-
-       blk_mq_complete_request(rq, ret);
+       cmd->ret = ret;
+       blk_mq_complete_request(cmd->rq, 0);
 }
 
 static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
@@ -1688,8 +1683,10 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
        ret = do_req_filebacked(lo, cmd->rq);
  failed:
        /* complete non-aio request */
-       if (!cmd->use_aio || ret)
-               blk_mq_complete_request(cmd->rq, ret ? -EIO : 0);
+       if (!cmd->use_aio || ret) {
+               cmd->ret = ret ? -EIO : 0;
+               blk_mq_complete_request(cmd->rq, 0);
+       }
 }
 
 static void loop_queue_work(struct kthread_work *work)
@@ -1715,6 +1712,7 @@ static int loop_init_request(void *data, struct request 
*rq,
 static const struct blk_mq_ops loop_mq_ops = {
        .queue_rq       = loop_queue_rq,
        .init_request   = loop_init_request,
+       .complete       = lo_complete_rq,
 };
 
 static int loop_add(struct loop_device **l, int i)
diff --git a/drivers/block/loop.h b/drivers/block/loop.h
index fb2237c73e61..fecd3f97ef8c 100644
--- a/drivers/block/loop.h
+++ b/drivers/block/loop.h
@@ -70,6 +70,7 @@ struct loop_cmd {
        struct request *rq;
        struct list_head list;
        bool use_aio;           /* use AIO interface to handle I/O */
+       long ret;
        struct kiocb iocb;
 };
 
-- 
2.11.0

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