[SCSI] Handle disk devices which can not process medium access commands

We have experienced several devices which fail in a fashion we do not
currently handle gracefully in SCSI. After a failure these devices will
respond to the SCSI primary command set (INQUIRY, TEST UNIT READY, etc.)
but any command accessing the storage medium will time out.

The following patch adds an callback that can be used by upper level
drivers to inspect the results of an error handling command. This in
turn has been used to implement additional checking in the SCSI disk
driver.

If a medium access command fails twice but TEST UNIT READY succeeds both
times in the subsequent error handling we will offline the device. The
maximum number of failed commands required to take a device offline can
be tweaked in sysfs.

Also add a new error flag to scsi_debug which allows this scenario to be
easily reproduced.

[jejb: fix up integer parsing to use kstrtouint]
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index 9be0128bf303..377df4a28512 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -10,6 +10,7 @@
 
 struct Scsi_Host;
 struct scsi_device;
+struct scsi_driver;
 
 /*
  * MAX_COMMAND_SIZE is:
@@ -131,6 +132,11 @@ struct scsi_cmnd {
 	unsigned char tag;	/* SCSI-II queued command tag */
 };
 
+static inline struct scsi_driver *scsi_cmd_to_driver(struct scsi_cmnd *cmd)
+{
+	return *(struct scsi_driver **)cmd->request->rq_disk->private_data;
+}
+
 extern struct scsi_cmnd *scsi_get_command(struct scsi_device *, gfp_t);
 extern struct scsi_cmnd *__scsi_get_command(struct Scsi_Host *, gfp_t);
 extern void scsi_put_command(struct scsi_cmnd *);