Hello, The following is the revised patch-set, fixing the issue pointed out by Jens and Benny. Changes from the previous post are below: o Rebased on top of 2.6.23-rc4-mm1 o Don't pass the lock held information (PATCH 01) o Removed sect2byte() macro (PATCH 02) o fixed blk_rq_size() and blk_rq_cur_size() for blk_pc_requests (PATCH 02) o Separated the patch for changes of end_that_request_* user (PATCH 03-26) o Removed the patch which changes the role of rq->end_io() from this patch-set because some more discussions are needed about it. Summary of each patch are below: 01/27: add new request completion interface, blk_end_request() 02/27: add some functions to get the size of request in bytes 03/27: convert to use blk_end_request() (core parts of block layer) 04/27: convert to use blk_end_request() (arm) 05/27: convert to use blk_end_request() (um) 06/27: convert to use blk_end_request() (DAC960) 07/27: convert to use blk_end_request() (floppy) 08/27: convert to use blk_end_request() (lguest) 09/27: convert to use blk_end_request() (nbd) 10/27: convert to use blk_end_request() (ps3disk) 11/27: convert to use blk_end_request() (sunvdc) 12/27: convert to use blk_end_request() (sx8) 13/27: convert to use blk_end_request() (ub) 14/27: convert to use blk_end_request() (viodasd) 15/27: convert to use blk_end_request() (xen-blkfront) 16/27: convert to use blk_end_request() (viocd) 17/27: convert to use blk_end_request() (i2o_block) 18/27: convert to use blk_end_request() (mmc) 19/27: convert to use blk_end_request() (s390) 20/27: convert to use blk_end_request() (scsi mid-layer) 21/27: convert to use blk_end_request() (ide-scsi) 22/27: convert to use blk_end_request() (xsysace) 23/27: convert to use blk_end_request() (cciss) 24/27: convert to use blk_end_request() (cpqarray) 25/27: convert to use blk_end_request() (normal parts of ide) 26/27: convert to use blk_end_request() (ide-cd, cdrom_newpc_intr()) 27/27: remove/unexport no longer needed end_that_request_* I have tested this patch-set on two machines, IA64+QLA1280+QLA2200 box and x86_64+SATA+IDE-CDROM box. Please review and apply. Below is the explanation about needs and details of this patch-set. SUMMARY ======= This set of patches changes request completion interface between device drivers and block layer to 1 step procedure from current 2 step procedures using end_that_request_{first/chunk} and end_that_request_last(). This patch-set prepares for realizing another patch-set which changes the role of rq->end_io(). It allows request-based multipath to hook in before completing each chunk of request, check errors for it and retry it using another path if error is detected. BACKGROUND ========== The patch-set which changes the role of rq->end_io() is necessary to allow device stacking at request level, that is request-based device-mapper multipath. Currently, device-mapper is implemented as a stacking block device at BIO level. OTOH, request-based dm will stack at request level to allow better multipathing decision. To allow device stacking at request level, the completion procedure need to provide a hook for it. For example, dm-multipath has to check errors and retry with other paths if necessary before returning the I/O result to upper layer. struct request has 'end_io' hook currently. But it's called at the very late stage of completion handling where the I/O result is already returned to the upper layer. So we need something here. The first approach to hook in completion of each chunk of request was adding a new rq->end_io_first() hook and calling it on the top of __end_that_request_first(). - http://marc.theaimsgroup.com/?l=linux-scsi&m=115520444515914&w=2 - http://marc.theaimsgroup.com/?l=linux-kernel&m=116656637425880&w=2 However, Jens pointed out that redesigning rq->end_io() as a full completion handler would be better: On Thu, 21 Dec 2006 08:49:47 +0100, Jens Axboe <jens.axboe@xxxxxxxxxx> wrote: > Ok, I see what you are getting at. The current ->end_io() is called when > the request has fully completed, you want notification for each chunk > potentially completed. > > I think a better design here would be to use ->end_io() as the full > completion handler, similar to how bio->bi_end_io() works. A request > originating from __make_request() would set something ala: ..... > instead of calling the functions manually. That would allow you to get > notification right at the beginning and do what you need, without adding > a special hook for this. I thought his comment was reasonable. So I modified the patches based on his suggestion. WHAT IS CHANGED =============== The change is basically illustlated by the following pseudo code: [Before] if (end_that_request_{first/chunk} succeeds) { <-- completes bios <do something driver specific> end_that_request_last() <-- calls end_io() <the request is free from the driver> } else { <the request was incomplete, retry for leftover or ignoring> } [After] if (blk_end_request() succeeds) { <-- calls end_io(), completes bios <the request is free from the driver> } else { <the request was incomplete, retry for leftover or ignoring> } In detail, request completion procedures are changed like below. [Before] o 2 steps completion using end_that_request_{first/chunk} and end_that_request_last(). o Device drivers have ownership of a request until they call end_that_request_last(). o rq->end_io() is called at the last stage of end_that_request_last() for some block layer codes need specific request handling when completing it. [After] o 1 step completion using blk_end_request(). (end_that_request_* are no longer used from device drivers.) o Device drivers give over ownership of a request when calling blk_end_request(). If it returns 0, the request is completed. If it returns 1, the request isn't completed and the ownership is returned to the device driver again. o rq->end_io() is called at the top of blk_end_request() to allow to hook all parts of request completion. Existing users of rq->end_io() must be changed to do all parts of request completion. Thanks, Kiyoshi Ueda -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel