Hello, Jeff.
On Wed, Aug 10, 2011 at 11:19:46AM -0400, Jeff Moyer wrote:
> @@ -1708,6 +1711,20 @@ int blk_insert_cloned_request(struct request_queue *q, struct request *rq)
> should_fail_request(&rq->rq_disk->part0, blk_rq_bytes(rq)))
> return -EIO;
>
> + if (rq->cmd_flags & (REQ_FLUSH|REQ_FUA)) {
> + /*
> + * Filter empty flush requests here. REQ_FLUSH_SEQ will
> + * ensure that no I/O accounting is done for this request.
> + */
> + if (!q->flush_flags && !blk_rq_sectors(rq)) {
> + blk_end_bidi_request(rq, 0, 0, 0);
> + return 0;
> + }
I wish the short-circuiting is in blk_insert_flush(). You can simply
test if (!policy) there and blk_insert_cloned_request() would behave
like other insertion paths.
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index 6395692..60cfd24 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -168,7 +168,18 @@ enum rq_flag_bits {
> #define REQ_COMMON_MASK \
> (REQ_WRITE | REQ_FAILFAST_MASK | REQ_SYNC | REQ_META | REQ_DISCARD | \
> REQ_NOIDLE | REQ_FLUSH | REQ_FUA | REQ_SECURE)
> -#define REQ_CLONE_MASK REQ_COMMON_MASK
> +/*
> + * Cloned requests are inserted into the elevator via blk_insert_cloned_request.
> + * Because the flush flags exported by the request-based dm target may in
> + * theory be different from the flush flags of the underlying request_queue,
> + * we need to pass along information regarding whether a particular request
> + * is part of a flush sequence. This is primarily used to complete I/Os early
> + * that would otherwise not be necessary (such as an empty flush for a request
> + * queue that does not support flush). In such a case, the end_io path for
> + * the request would try to account the I/O instead of ignoring it, resulting
> + * in a null pointer dereference.
> + */
> +#define REQ_CLONE_MASK (REQ_COMMON_MASK | REQ_FLUSH_SEQ)
I'm probably missing something, but why do we still need to copy
REQ_FLUSH_SEQ? Why doesn't the following work?
* dm driver always advertises REQ_FLUSH|FUA like other stacking
drivers.
* blk-flush for the dm, decomposes flushes to FLUSH + FUA write and
send it down.
* dm driver clones the requests and send them down to each member
queue.
* blk-flush on member queue, handles FLUSH as FLUSH and decomposes FUA
write as necessary.
What am I missing? Why does end_io path still matter when it goes
through blk-flush on the member device too?
Thank you.
--
tejun
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
