[SCSI] scsi_dh: add infrastructure for SCSI Device Handlers

Some of the storage devices (that can be accessed through multiple paths),
do need some special handling for
	1. Activating the passive path of the storage access.
	2. Decode and handle the special sense codes returned by the devices.
	3. Handle the I/Os being sent to the passive path, especially
           during the device probe time.
when accessed through multiple paths.

As of today this special device handling is done at the dm-multipath
layer using dm-handlers. That works well for (1); for (2) to be handled
at dm layer, scsi sense information need to be exported from SCSI to dm-layer,
which is not very attractive; (3) cannot be done at all at the dm layer.

Device handler has been moved to SCSI mainly to handle (2) and (3) properly.

Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: Mike Anderson <andmike@linux.vnet.ibm.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index eaf5a8add1ba..006a95916f72 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -298,6 +298,7 @@ static inline void scsi_eh_prt_fail_stats(struct Scsi_Host *shost,
  */
 static int scsi_check_sense(struct scsi_cmnd *scmd)
 {
+        struct scsi_device *sdev = scmd->device;
         struct scsi_sense_hdr sshdr;
 
         if (! scsi_command_normalize_sense(scmd, &sshdr))
@@ -306,6 +307,16 @@ static int scsi_check_sense(struct scsi_cmnd *scmd)
         if (scsi_sense_is_deferred(&sshdr))
                 return NEEDS_RETRY;
 
+        if (sdev->scsi_dh_data && sdev->scsi_dh_data->scsi_dh &&
+                        sdev->scsi_dh_data->scsi_dh->check_sense) {
+                int rc;
+
+                rc = sdev->scsi_dh_data->scsi_dh->check_sense(sdev, &sshdr);
+                if (rc != SCSI_RETURN_NOT_HANDLED)
+                        return rc;
+                /* handler does not care. Drop down to default handling */
+        }
+
         /*
          * Previous logic looked for FILEMARK, EOM or ILI which are
          * mainly associated with tapes and returned SUCCESS.