Messages in this thread | | | Date | Fri, 2 Jan 2004 11:46:37 +0100 | From | Jens Axboe <> | Subject | Re: [RFC][PATCH] Move bv_offset/bv_len update after bio_endio in __end_that_request_first |
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On Thu, Jan 01 2004, Christophe Saout wrote: > Hi! > > Can we move the update of bio_index(bio)->bv_offset and bv_len after the > bio_endio call in __end_that_request_first please (if a bvec is partially > completed)? > > The bi_idx is currently also updated after the bio_endio call. > > Currently the bi_end_io function cannot exactly determine whether a bvec > was completed or not. > > Think of the following situation: > > bv_offset is 0 and bv_len is 4096, now the driver completes 2048 bytes of > that bvec. > > At the moment bv_offset and bv_len are set to 2048 first. The bi_end_io > function can't distinguish between this situation and the situation where > bv_offset and bv_len were 2048 before and that bvec was completed (because > bi_idx is incremented afterwards). > > This shouldn't break any user since most users are waiting for the whole > bio to complete with if (bio->bi_size > 0) return 1;. > > I need this because I want to release buffers as soon as possible. The > incoming bio can get split by my driver due to problems allocating buffers. > If the partial bio returns and can't release its buffers immediately the > whole thing might deadlock. > > That's why I need to know exactly how many and which bvecs were completed > in my bi_end_io function. > > Or do you think it is safer to count backwards using bi_vcnt and bi_size?
I'm inclined to thinking that, indeed. Those two fields have a more well established usage, so I think you'll be better off doing that in the long run.
-- Jens Axboe
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