[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>

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 1e7c9e9ef772e10c40789ebf44eb428360ac7f77..f5d3b96890dc6d9dd180eb86bb0f2b737a60e7f1 100644 (file)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -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;
 }