Messages in this thread | | | Date | Tue, 31 Jul 2007 09:44:41 +0200 | From | Jens Axboe <> | Subject | Re: bi_end_io question |
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On Tue, Jul 31 2007, Dmitry Monakhov wrote: > On 09:29 ?????? 31 ?????? , Jens Axboe wrote: > > On Tue, Jul 31 2007, Dmitry Monakhov wrote: > > > I want implement some sort of snapshot dev. > > > In order to do this i've replaced original q->make_request_fn > > > with specific one which cowed all write requests. > > > My first attempt looks like this: > > > static int mysnap_make_request(request_queue_t *q, struct bio *bio) > > > { > > > struct bio cl_bio; > > > make_request_fn *fn = get_original_make_fn(q); > > > if(bio->bi_rw & (1 << BIO_RW){ > > > /* This is write request, so we have to cow it first*/ > > > cl_bio = clone_bio(bio); > > > submit_bio(READ, &cl_bio); > > > wait_for_completion(&complete); > > > save_cowed_bio(&cl_bio); > > > /* At this time old data has successfully saved in cow > > > * area so we may safely perform original request */ > > > } > > > /* call original make_request_fn function for bio*/ > > > return fn(q, bio); > > > } > > > But this implementation has significance performance drawback because > > > of waiting for read request completion. > > > > > > So i want use a-sync implementation: > > > static int my_make_original_request(struct bio *bio, unsigned int bytes_done, > > > int err) > > > { > > > if(bio->bi_size == 0) { > > > /* restore original request info */ > > > struct pending_request* pr = bio->bi_private; > > > /* make original write request */ > > > ret = pr->fn(pr->q, pr->bio); > > > /* error handling logic here*/ > > > } > > > } > > > static int mysnap_make_request_v2(request_queue_t *q, struct bio *bio) > > > { > > > struct bio cl_bio; > > > make_request_fn *fn = get_original_make_fn(q); > > > if(bio->bi_rw & (1 << BIO_RW){ > > > /* This is write request, so we have to cow it first*/ > > > cl_bio = clone_bio(bio); > > > cl_bio->bi_private = store_request(fn, q, bio) > > > cl_bio->bi_end_io = my_make_original_request; > > > /* after read request ended original write request > > > * will be queued */ > > > submit_bio(READ, &cl_bio, q); > > > /* We dont have to wait submitted bio here any more, > > > * because write request will be automaticaly queued > > > * by cl_bio->bi_end_io callcack. > > > * All job has been done at this moment. > > > */ > > > return 0; > > > } > > > /* call original make_request_fn function for bio*/ > > > return fn(q, bio); > > > } > > > My question is following: > > > 1)Can i safely call make_request_fn from ->bi_end_io callback > > > (as it done in my_make_original_request function) > > > > No, make_request_fn must be called from process context. > > > > > 2)May be you have any other sound idea? > > > > Allocate a real clone, if you want to do handle it async. > what do you mean by "real clone" ?
One that isn't allocated on the stack.
-- Jens Axboe
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