From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH] block: Make __bio_clone_fast() copy bi_vcnt To: Ming Lei Cc: Jens Axboe , "linux-block@vger.kernel.org" , Christoph Hellwig , Mike Snitzer , Hannes Reinecke , Johannes Thumshirn References: <20180627201231.15641-1-bart.vanassche@wdc.com> <20180627235005.GE7583@ming.t460p> From: Bart Van Assche Message-ID: <4995fc0c-e9d7-d747-7331-67396827a596@wdc.com> Date: Wed, 27 Jun 2018 16:59:41 -0700 MIME-Version: 1.0 In-Reply-To: <20180627235005.GE7583@ming.t460p> Content-Type: text/plain; charset=utf-8; format=flowed List-ID: On 06/27/18 16:50, Ming Lei wrote: > On Wed, Jun 27, 2018 at 01:12:31PM -0700, Bart Van Assche wrote: >> Although __bio_clone_fast() copies bi_io_vec, it does not copy bi_vcnt, >> the number of elements in bi_io_vec[] that contains data. Copy bi_vcnt >> such that code that needs this member behaves identically for original >> and for cloned requests. >> >> Signed-off-by: Bart Van Assche >> Cc: Christoph Hellwig >> Cc: Mike Snitzer >> Cc: Ming Lei >> Cc: Hannes Reinecke >> Cc: Johannes Thumshirn >> --- >> block/bio.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/block/bio.c b/block/bio.c >> index f7e3d88bd0b6..55f8e0dedd69 100644 >> --- a/block/bio.c >> +++ b/block/bio.c >> @@ -605,6 +605,7 @@ void __bio_clone_fast(struct bio *bio, struct bio *bio_src) >> bio->bi_opf = bio_src->bi_opf; >> bio->bi_write_hint = bio_src->bi_write_hint; >> bio->bi_iter = bio_src->bi_iter; >> + bio->bi_vcnt = bio_src->bi_vcnt; >> bio->bi_io_vec = bio_src->bi_io_vec; > > No, don't do that. Why not? I think it's a huge booby trap that cloned bio's have a bi_io_vec but zero bi_vcnt. > For a cloned bio, both .bi_vcnt and .bi_io_vec can't be used directly, > and we have done huge such cleanup for supporting multipage bvec, that is > the great idea of immutable bvecs invented by Kent. My understanding is that the above change doesn't conflict at all with the immutable biovec work -- to the contrary. Bart.