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[SCSI] scsi_dh: add infrastructure for SCSI Device Handlers

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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>
This commit is contained in:
Chandra Seetharaman
2008-05-01 14:49:46 -07:00
committed by James Bottomley
parent 53c8ba9540
commit a6a8d9f87e
11 changed files with 283 additions and 0 deletions
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8
drivers/scsi/scsi_lib.c
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@@ -1160,6 +1160,14 @@ int scsi_setup_fs_cmnd(struct scsi_device *sdev, struct request *req)
if (ret != BLKPREP_OK)
return ret;
if (unlikely(sdev->scsi_dh_data && sdev->scsi_dh_data->scsi_dh
&& sdev->scsi_dh_data->scsi_dh->prep_fn)) {
ret = sdev->scsi_dh_data->scsi_dh->prep_fn(sdev, req);
if (ret != BLKPREP_OK)
return ret;
}
/*
* Filesystem requests must transfer data.
*/