Messages in this thread | | | Date | Tue, 31 Jul 2007 11:41:49 +0400 | From | Dmitry Monakhov <> | Subject | Re: bi_end_io question |
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On 09:29 Втр 31 Июл , 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" ? > > -- > Jens Axboe > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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