> Hi James,
>
> I hope the previous RFC patch(*) would be no problem, since I haven't
> gotten any negative comment.
> (*)
http://lkml.org/lkml/2008/9/25/262
>
> So could you take this patch for 2.6.28 additionally?
> This patch implements a new interface of the block layer for
> request stacking drivers.
> There should be no effect on existing drivers' behavior.
>
> This patch was created on top of the commit below of scsi-post-merge-2.6.
> ---------------------------------------------------------------------
> commit e49f03f37104c0e7cae7c455480069bada00932f
> Author: James Bottomley <James.Bottomley@HansenPartnership.com>
> Date: Fri Sep 12 16:46:51 2008 -0500
>
> [SCSI] scsi_error: fix target reset handling
> ---------------------------------------------------------------------
>
> And this patch depends on the following block layer patch, which
> is in Jens' for-2.6.28 of linux-2.6-block.
>
http://lkml.org/lkml/2008/9/29/142
>
> Thanks,
> Kiyoshi Ueda
>
>
> Subject: [PATCH 1/1] scsi: export busy state via q->lld_busy_fn()
>
> This patch implements q->lld_busy_fn() for scsi mid layer to export
> its busy state.
>
> Please note that it checks the cached information (sdev->lld_busy)
> for efficiency, instead of checking the actual state of
> sdev/starget/shost everytime.
>
> So the care must be taken not to leave sdev->lld_busy = 1 for
> the following cases:
> - when there is no request in the sdev queue
> - when scsi can't dispatch I/Os anymore and needs to kill I/Os
> Otherwise, request stacking drivers may not submit any request,
> and then, nobody sets back lld_busy = 0 and that causes deadlock.
>
> OTOH, it has no major problem in setting sdev->lld_busy = 0 even when
> the starget/shost is actually busy, because newly submitted request
> will soon turn it to 1 in scsi_request_fn().
>
>
> Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Mike Christie <michaelc@cs.wisc.edu>
> Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
> ---
> drivers/scsi/scsi.c | 4 ++--
> drivers/scsi/scsi_lib.c | 20 +++++++++++++++++++-
> include/scsi/scsi_device.h | 13 +++++++++++++
> 3 files changed, 34 insertions(+), 3 deletions(-)
>
> Index: scsi-post-merge-2.6/drivers/scsi/scsi_lib.c
> ===================================================================
> --- scsi-post-merge-2.6.orig/drivers/scsi/scsi_lib.c
> +++ scsi-post-merge-2.6/drivers/scsi/scsi_lib.c
> @@ -480,6 +480,8 @@ void scsi_device_unbusy(struct scsi_devi
> spin_unlock(shost->host_lock);
> spin_lock(sdev->request_queue->queue_lock);
> sdev->device_busy--;
> + if (sdev->device_busy < sdev->queue_depth && !sdev->device_blocked)
> + sdev->lld_busy = 0;
> spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags);
> }
>
> @@ -1535,6 +1537,13 @@ static void scsi_softirq_done(struct req
> }
> }
>
> +static int scsi_lld_busy(struct request_queue *q)
> +{
> + struct scsi_device *sdev = q->queuedata;
> +
> + return sdev ? sdev->lld_busy : 0;
> +}
