Messages in this thread | | | Date | Tue, 31 Jul 2007 11:10:43 +0400 | From | Dmitry Monakhov <> | Subject | bi_end_io question |
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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) 2)May be you have any other sound idea?
thank you.
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