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Commit a58a935d authored by Mike Snitzer's avatar Mike Snitzer Committed by Alasdair G Kergon
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dm mpath: add retain_attached_hw_handler feature



A SCSI device handler might get attached to a device during the
initial device scan.  We do not necessarily want to override
this when loading a multipath table, so this patch adds a new
multipath feature argument "retain_attached_hw_handler".

During SCSI device scan all loaded SCSI device handlers will be
consulted for a match (via scsi_dh's provided .match).  If a match is
found that device handler will be attached.  We need a way to have
userspace multipathd's provided 'hw_handler' not override the already
attached hardware handler.

When specifying the new feature 'retain_attached_hw_handler' multipath
will use the currently attached hardware handler instead of trying to
attach the one specified during table load.  If no hardware handler is
attached the specified hardware handler will still be used.

Leverages scsi_dh_attach's ability to increment the scsi_dh's reference
count if the same scsi_dh name is provided when attaching - currently
attached scsi_dh name is determined with scsi_dh_attached_handler_name.

Depends upon commit 7e8a74b1
("[SCSI] scsi_dh: add scsi_dh_attached_handler_name").

Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Tested-by: default avatarBabu Moger <babu.moger@netapp.com>
Reviewed-by: default avatarChandra Seetharaman <sekharan@us.ibm.com>
Acked-by: default avatarHannes Reinecke <hare@suse.de>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent f9a8e0cd
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