From 1954e9a998d59d08520d7d4bebeafb8f66ba0d0f Mon Sep 17 00:00:00 2001 From: Bart Van Assche Date: Wed, 27 Jun 2018 13:09:05 -0700 Subject: [PATCH] block: Document how blk_update_request() handles RQF_SPECIAL_PAYLOAD requests The payload of struct request is stored in the request.bio chain if the RQF_SPECIAL_PAYLOAD flag is not set and in request.special_vec if RQF_SPECIAL_PAYLOAD has been set. However, blk_update_request() iterates over req->bio whether or not RQF_SPECIAL_PAYLOAD has been set. Additionally, the RQF_SPECIAL_PAYLOAD flag is ignored by blk_rq_bytes() which means that the value returned by that function is incorrect if the RQF_SPECIAL_PAYLOAD flag has been set. It is not clear to me whether this is an oversight or whether this happened on purpose. Anyway, document that it is known that both functions ignore RQF_SPECIAL_PAYLOAD. See also commit f9d03f96b988 ("block: improve handling of the magic discard payload"). Reviewed-by: Christoph Hellwig Signed-off-by: Bart Van Assche Cc: Ming Lei Signed-off-by: Jens Axboe --- block/blk-core.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/block/blk-core.c b/block/blk-core.c index 947e7a4abd8c..2ff8e131a892 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -3056,6 +3056,10 @@ EXPORT_SYMBOL_GPL(blk_steal_bios); * Passing the result of blk_rq_bytes() as @nr_bytes guarantees * %false return from this function. * + * Note: + * The RQF_SPECIAL_PAYLOAD flag is ignored on purpose in both + * blk_rq_bytes() and in blk_update_request(). + * * Return: * %false - this request doesn't have any more data * %true - this request has more data