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[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 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>
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1 changed files with 32 additions and 0 deletions
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@ -1464,6 +1464,37 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
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return 1;
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}
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/*
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* Busy state exporting function for request stacking drivers.
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*
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* For efficiency, no lock is taken to check the busy state of
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* shost/starget/sdev, since the returned value is not guaranteed and
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* may be changed after request stacking drivers call the function,
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* regardless of taking lock or not.
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*
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* When scsi can't dispatch I/Os anymore and needs to kill I/Os
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* (e.g. !sdev), scsi needs to return 'not busy'.
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* Otherwise, request stacking drivers may hold requests forever.
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*/
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static int scsi_lld_busy(struct request_queue *q)
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{
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struct scsi_device *sdev = q->queuedata;
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struct Scsi_Host *shost;
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struct scsi_target *starget;
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if (!sdev)
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return 0;
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shost = sdev->host;
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starget = scsi_target(sdev);
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if (scsi_host_in_recovery(shost) || scsi_host_is_busy(shost) ||
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scsi_target_is_busy(starget) || scsi_device_is_busy(sdev))
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return 1;
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return 0;
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}
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/*
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* Kill a request for a dead device
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*/
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@ -1767,6 +1798,7 @@ struct request_queue *scsi_alloc_queue(struct scsi_device *sdev)
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blk_queue_prep_rq(q, scsi_prep_fn);
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blk_queue_softirq_done(q, scsi_softirq_done);
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blk_queue_rq_timed_out(q, scsi_times_out);
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blk_queue_lld_busy(q, scsi_lld_busy);
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return q;
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}
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