Re: [RFC 0/5] block large commands support continue

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

On Thu, Apr 24 2008, FUJITA Tomonori wrote:
> On Thu, 24 Apr 2008 13:31:21 +0900
> FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> wrote:
> 
> > On Wed, 23 Apr 2008 17:50:42 +0300
> > Boaz Harrosh <bharrosh@panasas.com> wrote:
> > 
> > > 
> > > The support for large commands was dropped from the for-2.6.26 branch
> > > and will probably not get accepted into next kernel.
> > > 
> > > I have tried to take all comments from Jens and Bart. and incorporate
> > > it into a new patchset. This is basically Tomo's patchset but with
> > > proposed changes.
> > 
> > Have you seen the patchset to remove request on the stack?
> > 
> > http://marc.info/?l=linux-ide&m=120882410712466&w=2
> > 
> > 
> > > They are based on current linux-block/master. They will probably conflict with
> > > latest patch sent by Tomo for the blk_get_request(). Once those patches
> > > get accepted at some git tree, (Where will that be?), I will rebase these
> > > on top of them. Please CC me of any progress.
> > > 
> > > [PATCH 1/5] block: no need to initialize rq->cmd
> > >   This is 2 of Tomo's patches squashed together as they are
> > >   small and do the same. Tomo is this OK?
> > > 
> > > [PATCH 2/5] block: replace sizeof(rq->cmd) with BLK_MAX_CDB
> > >   Tomos patch rebased to here
> > > 
> > > [PATCH 3/5] block: Export rq_init, rename to blk_init_rq
> > > [PATCH 4/5] block: Use new blk_init_rq
> > >   These patches are basically what Jens and Bart has suggested, that with
> > >   a small code change to blk-core.c we can memset at rq_init() and only set
> > >   none zero members. We can also export that initializer and use it all over
> > >   the ide tree where ever requests don't come from a request queue. (OK also
> > >   at scsi_error.c)
> > 
> > +void blk_init_rq(struct request_queue *q, struct request *rq, int cmd_flags)
> > 
> > Hmm, would it be better to modify the block layer to let rq_init just
> > memset() the request structure?
> 
> I think, if we move rq_init to blk_alloc_request from get_request,
> rq_init can just memset() the structure.
> 
> Then we can export rq_init and rq_init works for everyone.

Wont work, see the io scheduler set_request() functions.

> 
> 
> diff --git a/block/blk-barrier.c b/block/blk-barrier.c
> index 55c5f1f..722140a 100644
> --- a/block/blk-barrier.c
> +++ b/block/blk-barrier.c
> @@ -143,10 +143,8 @@ static void queue_flush(struct request_queue *q, unsigned which)
>  		end_io = post_flush_end_io;
>  	}
>  
> -	rq->cmd_flags = REQ_HARDBARRIER;
>  	rq_init(q, rq);
> -	rq->elevator_private = NULL;
> -	rq->elevator_private2 = NULL;
> +	rq->cmd_flags = REQ_HARDBARRIER;
>  	rq->rq_disk = q->bar_rq.rq_disk;
>  	rq->end_io = end_io;
>  	q->prepare_flush_fn(q, rq);
> @@ -167,14 +165,11 @@ static inline struct request *start_ordered(struct request_queue *q,
>  	blkdev_dequeue_request(rq);
>  	q->orig_bar_rq = rq;
>  	rq = &q->bar_rq;
> -	rq->cmd_flags = 0;
>  	rq_init(q, rq);
>  	if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
>  		rq->cmd_flags |= REQ_RW;
>  	if (q->ordered & QUEUE_ORDERED_FUA)
>  		rq->cmd_flags |= REQ_FUA;
> -	rq->elevator_private = NULL;
> -	rq->elevator_private2 = NULL;
>  	init_request_from_bio(rq, q->orig_bar_rq->bio);
>  	rq->end_io = bar_end_io;
>  
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 2a438a9..e447799 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -107,40 +107,18 @@ struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev)
>  }
>  EXPORT_SYMBOL(blk_get_backing_dev_info);
>  
> -/*
> - * We can't just memset() the structure, since the allocation path
> - * already stored some information in the request.
> - */
>  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;
> -	memset(rq->cmd, 0, sizeof(rq->cmd));
> -	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;
>  }
>  
>  static void req_bio_endio(struct request *rq, struct bio *bio,
> @@ -607,6 +585,8 @@ blk_alloc_request(struct request_queue *q, int rw, int priv, gfp_t gfp_mask)
>  	if (!rq)
>  		return NULL;
>  
> +	rq_init(q, rq);
> +
>  	/*
>  	 * first three bits are identical in rq->cmd_flags and bio->bi_rw,
>  	 * see bio.h and blkdev.h
> @@ -789,8 +769,6 @@ rq_starved:
>  	if (ioc_batching(q, ioc))
>  		ioc->nr_batch_requests--;
>  
> -	rq_init(q, rq);
> -
>  	blk_add_trace_generic(q, bio, rw, BLK_TA_GETRQ);
>  out:
>  	return rq;

-- 
Jens Axboe