From mboxrd@z Thu Jan 1 00:00:00 1970 From: FUJITA Tomonori Subject: Re: [PATCH 4/4] block: add large command support Date: Mon, 14 Apr 2008 21:08:32 +0900 Message-ID: <20080414210826Y.tomof@acm.org> References: <1208170266-1676-4-git-send-email-fujita.tomonori@lab.ntt.co.jp> <1208170266-1676-5-git-send-email-fujita.tomonori@lab.ntt.co.jp> <20080414112919.GF12774@kernel.dk> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Received: from mo11.iij4u.or.jp ([210.138.174.79]:36743 "EHLO mo11.iij4u.or.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753261AbYDNMJI (ORCPT ); Mon, 14 Apr 2008 08:09:08 -0400 In-Reply-To: <20080414112919.GF12774@kernel.dk> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: jens.axboe@oracle.com Cc: fujita.tomonori@lab.ntt.co.jp, linux-scsi@vger.kernel.org, bharrosh@panasas.com, linux-ide@vger.kernel.org On Mon, 14 Apr 2008 13:29:20 +0200 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 > > Cc: Jens Axboe > > --- > > 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; > > } > > > > EXPORT_SYMBOL(ide_init_drive_cmd); > > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h > > index b3a58ad..5710ae4 100644 > > --- a/include/linux/blkdev.h > > +++ b/include/linux/blkdev.h > > @@ -215,8 +215,9 @@ struct request { > > /* > > * when request is used as a packet command carrier > > */ > > - unsigned int cmd_len; > > - unsigned char cmd[BLK_MAX_CDB]; > > + unsigned short cmd_len; > > + unsigned char __cmd[BLK_MAX_CDB]; > > + unsigned char *cmd; > > > > unsigned int data_len; > > unsigned int extra_len; /* length of alignment and padding */ > > @@ -812,6 +813,13 @@ static inline void put_dev_sector(Sector p) > > page_cache_release(p.v); > > } > > > > +static inline void rq_set_cmd(struct request *rq, unsigned char *cmd, > > + unsigned short cmd_len) > > +{ > > + rq->cmd = cmd; > > + rq->cmd_len = cmd_len; > > +} > > + > > This is 100% identical to what I suggested be done instead, so of course > I agree with this. Yeah, I think that it's the most straightforward. We have one value to represent one item, the length of command. We can access to rq->cmd and rq->cmd_len as before. I don't see how it's is dangerous to have a single value to represent the length of command though changing rq->cmd from the static array to a pointer to support large commands is tricky. It's possible that I overlooked something that uses the block layer in an uncommon way as ide does.