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[SCSI] export busy state via q->lld_busy_fn()

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This patch implements q->lld_busy_fn() for scsi mid layer to export
its busy state for request stacking drivers.

For efficiency, no lock is taken to check the busy state of
shost/starget/sdev, since the returned value is not guaranteed and
may be changed after request stacking drivers call the function,
regardless of taking lock or not.

When scsi can't dispatch I/Os anymore and needs to kill I/Os
(e.g. !sdev), scsi needs to return 'not busy'.
Otherwise, request stacking drivers may hold requests forever.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
This commit is contained in:
Kiyoshi Ueda 2008-10-04 14:11:35 -04:00 committed by James Bottomley
parent 9d11251709
commit 6c5121b78b
1 changed files with 32 additions and 0 deletions
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32
drivers/scsi/scsi_lib.c
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@ -1464,6 +1464,37 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
return 1;
}
/*
* Busy state exporting function for request stacking drivers.
*
* For efficiency, no lock is taken to check the busy state of
* shost/starget/sdev, since the returned value is not guaranteed and
* may be changed after request stacking drivers call the function,
* regardless of taking lock or not.
*
* When scsi can't dispatch I/Os anymore and needs to kill I/Os
* (e.g. !sdev), scsi needs to return 'not busy'.
* Otherwise, request stacking drivers may hold requests forever.
*/
static int scsi_lld_busy(struct request_queue *q)
{
struct scsi_device *sdev = q->queuedata;
struct Scsi_Host *shost;
struct scsi_target *starget;
if (!sdev)
return 0;
shost = sdev->host;
starget = scsi_target(sdev);
if (scsi_host_in_recovery(shost) || scsi_host_is_busy(shost) ||
scsi_target_is_busy(starget) || scsi_device_is_busy(sdev))
return 1;
return 0;
}
/*
* Kill a request for a dead device
*/
@ -1767,6 +1798,7 @@ struct request_queue *scsi_alloc_queue(struct scsi_device *sdev)
blk_queue_prep_rq(q, scsi_prep_fn);
blk_queue_softirq_done(q, scsi_softirq_done);
blk_queue_rq_timed_out(q, scsi_times_out);
blk_queue_lld_busy(q, scsi_lld_busy);
return q;
}