On Thu, Apr 17, 2008 at 9:07 AM, Jens Axboe <jens.axboe@xxxxxxxxxx> wrote:
>
> On Thu, Apr 17 2008, FUJITA Tomonori wrote:
> > On Wed, 16 Apr 2008 12:08:25 +0300
> > Boaz Harrosh <bharrosh@xxxxxxxxxxx> wrote:
> >
> > > On Wed, Apr 16 2008 at 11:33 +0300, Jens Axboe <jens.axboe@xxxxxxxxxx> wrote:
> > > > On Wed, Apr 16 2008, FUJITA Tomonori wrote:
> > > >> On Wed, 16 Apr 2008 00:50:54 +0200
> > > >> Bartlomiej Zolnierkiewicz <bzolnier@xxxxxxxxx> 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@xxxxxxxxxxxxx>
> > > >>>>> Cc: Jens Axboe <jens.axboe@xxxxxxxxxx>
> > > >>>>> ---
> > > >>>>> 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@xxxxxxxxxxx>
> > > 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@xxxxxxxxxxx>
> > > ---
> > > 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));
> >
> > Hmm, rq_init comment says:
> >
> > /*
> > * We can't just memset() the structure, since the allocation path
> > * already stored some information in the request.
> > */
> >
> > I think that we can't initialize rq->cmd_flags here.
>
> That is correct, the patch wont work as-is. The principle of clearing
> every member except block internal is sound and should be applied,
> though.
While we're at it we may fix it as well (preferably in another pre-patch):
- move setting rq->cmd_flags from blk_alloc_request() to the callers
(this is only get_request() ATM)
- re-order setting rq->cmd_flags vs calling rq_init() in get_request(),
queue_lfush() and start_ordered()
Thanks,
Bart
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