linux-kernel - Re: bi_end

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20070731074149.GC19019@dnb.sw.ru>
Date:	Tue, 31 Jul 2007 11:41:49 +0400
From:	Dmitry Monakhov <dmonakhov@...ru>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: bi_end_io question

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@...r.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/