Re: [PATCH 4/4] block: add large command support

[Jens Axboe <jens.axboe@oracle.com>]

On Wed, Apr 16 2008, Boaz Harrosh wrote:
> On Wed, Apr 16 2008 at 11:33 +0300, Jens Axboe <jens.axboe@oracle.com> wrote:
> > On Wed, Apr 16 2008, FUJITA Tomonori wrote:
> >> On Wed, 16 Apr 2008 00:50:54 +0200
> >> Bartlomiej Zolnierkiewicz <bzolnier@gmail.com> wrote:
> >>
> >>> Hi,
> >>>
> >>> On Monday 14 April 2008, Jens Axboe wrote:
> >>>> On Mon, Apr 14 2008, FUJITA Tomonori wrote:
> >>>>> This patch changes rq->cmd from the static array to a pointer to
> >>>>> support large commands.
> >>>>>
> >>>>> We rarely handle large commands. So for optimization, a struct request
> >>>>> still has a static array for a command. rq_init sets rq->cmd pointer
> >>>>> to the static array.
> >>>>>
> >>>>> Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
> >>>>> Cc: Jens Axboe <jens.axboe@oracle.com>
> >>>>> ---
> >>>>>  block/blk-core.c       |    1 +
> >>>>>  drivers/ide/ide-io.c   |    1 +
> >>>>>  include/linux/blkdev.h |   12 ++++++++++--
> >>>>>  3 files changed, 12 insertions(+), 2 deletions(-)
> >>>>>
> >>>>> diff --git a/block/blk-core.c b/block/blk-core.c
> >>>>> index 6669238..6f0968f 100644
> >>>>> --- a/block/blk-core.c
> >>>>> +++ b/block/blk-core.c
> >>>>> @@ -132,6 +132,7 @@ void rq_init(struct request_queue *q, struct request *rq)
> >>>>>  	rq->errors = 0;
> >>>>>  	rq->ref_count = 1;
> >>>>>  	rq->cmd_len = 0;
> >>>>> +	rq->cmd = rq->__cmd;
> >>>>>  	memset(rq->cmd, 0, BLK_MAX_CDB);
> >>>>>  	rq->data_len = 0;
> >>>>>  	rq->extra_len = 0;
> >>>>> diff --git a/drivers/ide/ide-io.c b/drivers/ide/ide-io.c
> >>>>> index 7153796..bac5ea1 100644
> >>>>> --- a/drivers/ide/ide-io.c
> >>>>> +++ b/drivers/ide/ide-io.c
> >>>>> @@ -1595,6 +1595,7 @@ void ide_init_drive_cmd (struct request *rq)
> >>>>>  {
> >>>>>  	memset(rq, 0, sizeof(*rq));
> >>>>>  	rq->ref_count = 1;
> >>>>> +	rq->cmd = rq->__cmd;
> >>>>>  }
> >>> Tomo, some more changes are needed:
> >>>
> >>> Please think about all _static_/dynamic allocations of 'struct request'
> >>> used together with REQ_TYPE_SPECIAL etc., i.e.
> >> I think that using struct request allocated statically is wrong from
> >> the perspective of the block layer design, that is, you always need to
> >> use blk_get_request. I think that except ide, everyone does.
> >>
> >> I try to convert ide to use blk_get_request properly if you want.
> > 
> > That would be best, but the on-stack allocation has the benefit that
> > it'll always work. So until we can completely get rid of that, lets just
> > make it a hard rule that ANY rq allocation MUST call rq_init(). It's a
> > lot saner than doing a memset() anyway.
> > 
> 
> Just a patch that I had for ages since the bad old request bidi times,
> perhaps is also good today. (rebased to for-2.6.26 branch)
> ---
> From: Boaz Harrosh <bharrosh@panasas.com>
> Date: Wed, 16 Apr 2008 12:05:33 +0300
> Subject: [PATCH] Initialize all members of struct request in rq_init
> 
> Before, every member added/removed from struct request would entitle a change
> to rq_init, for initialization. Now all members are default to zero and only
> the none zero members are specifically initialized.
> 
> Users that need requests on the stack or pre-allocated, must call rq_init()
> before use.
> 
> Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
> ---
>  block/blk-core.c |   22 ++--------------------
>  1 files changed, 2 insertions(+), 20 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 6f0968f..3f4c563 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -113,36 +113,18 @@ EXPORT_SYMBOL(blk_get_backing_dev_info);
>   */
>  void rq_init(struct request_queue *q, struct request *rq)
>  {
> +	memset(rq, 0, sizeof(*rq));
>  	INIT_LIST_HEAD(&rq->queuelist);
>  	INIT_LIST_HEAD(&rq->donelist);
>  	rq->q = q;
>  	rq->sector = rq->hard_sector = (sector_t) -1;
> -	rq->nr_sectors = rq->hard_nr_sectors = 0;
> -	rq->current_nr_sectors = rq->hard_cur_sectors = 0;
> -	rq->bio = rq->biotail = NULL;
>  	INIT_HLIST_NODE(&rq->hash);
>  	RB_CLEAR_NODE(&rq->rb_node);
> -	rq->rq_disk = NULL;
> -	rq->nr_phys_segments = 0;
> -	rq->nr_hw_segments = 0;
> -	rq->ioprio = 0;
> -	rq->special = NULL;
> -	rq->buffer = NULL;
>  	rq->tag = -1;
> -	rq->errors = 0;
>  	rq->ref_count = 1;
> -	rq->cmd_len = 0;
>  	rq->cmd = rq->__cmd;
> -	memset(rq->cmd, 0, BLK_MAX_CDB);
> -	rq->data_len = 0;
> -	rq->extra_len = 0;
> -	rq->sense_len = 0;
> -	rq->data = NULL;
> -	rq->sense = NULL;
> -	rq->end_io = NULL;
> -	rq->end_io_data = NULL;
> -	rq->next_rq = NULL;
>  }
> +EXPORT_SYMBOL(rq_init);
>  
>  static void req_bio_endio(struct request *rq, struct bio *bio,
>  			  unsigned int nbytes, int error)
> -- 
> 1.5.3.3
> 

Totally agree, if we expand rq_init() to all users (including on stack),
this must be included as well.

-- 
Jens Axboe