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Date: Thu, 11 Jun 2009 12:17:25 +0900 From: Kiyoshi Ueda <k-ueda@...jp.nec.com> To: Jens Axboe <jens.axboe@...cle.com> CC: linux-kernel@...r.kernel.org, device-mapper development <dm-devel@...hat.com>, "Jun'ichi Nomura" <j-nomura@...jp.nec.com>, Boaz Harrosh <bharrosh@...asas.com>, k-ueda@...jp.nec.com Subject: Re: [PATCH block#for-2.6.31] block: add request clone interface Hi Jens, On 06/10/2009 01:30 PM +0900, Jens Axboe wrote: > On Wed, Jun 10 2009, Kiyoshi Ueda wrote: >> On 06/10/2009 03:03 AM +0900, Jens Axboe wrote: >>> On Tue, Jun 09 2009, Kiyoshi Ueda wrote: >>>> Hi Jens, >>>> >>>> +/* >>>> + * Copy request information of the original request to the clone request. >>>> + */ >>>> +static void __blk_rq_prep_clone(struct request *dst, struct request *src) >>>> +{ >>>> + dst->cpu = src->cpu; >>>> + dst->cmd_flags = (rq_data_dir(src) | REQ_NOMERGE); >>>> + dst->cmd_type = src->cmd_type; >>>> + dst->__sector = blk_rq_pos(src); >>>> + dst->__data_len = blk_rq_bytes(src); >>>> + dst->nr_phys_segments = src->nr_phys_segments; >>>> + dst->ioprio = src->ioprio; >>>> + dst->buffer = src->buffer; >>>> + dst->cmd_len = src->cmd_len; >>>> + dst->cmd = src->cmd; >>> Are you making sure that 'src' always exists while 'dst' is alive? >> Yes. >> Request-based dm is the owner of 'src' (original) and >> it never frees 'src' until the 'dst' (clone) are completed. >> >> I avoided deep-copying __cmd/buffer/sense as it's costly >> (additional allocation and memcpy). >> And I don't think there are any needs for that. >> But if anyone really wants that even with the copying cost, >> please speak up. > > I just worry that the interface is easy to misuse. You don't document > the requirement that the src request may not go away while dst is used, > yet it's an important fact. The function advertises itself as a copy, > you would not normally expect any such restrictions. OK, I see. Since forcing such restrictions by code-level is pretty difficult (e.g. bio also points pages which are not copied), I'd like to put documents for this. Please see the updated patch also reflecting Boaz's comments: http://marc.info/?l=dm-devel&m=124468991432260&w=2 Thanks, Kiyoshi Ueda -- 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/
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