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

[Boaz Harrosh <bharrosh@panasas.com>]

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