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[SCSI] cciss: scsi error handling

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This patch adds SCSI error handling code to the SCSI portion
of the cciss driver.

Signed-off-by: Stephen M. Cameron <steve.cameron@hp.com>
Acked-by: Mike Miller <mike.miller@hp.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
This commit is contained in:
mike.miller@hp.com
2005-11-04 12:30:37 -06:00
committed by James Bottomley
parent 13bf50d1f2
commit 3da8b713da
4 changed files with 283 additions and 27 deletions
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Documentation/cciss.txt
+29
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@@ -133,3 +133,32 @@ hardware and it is important to prevent the kernel from attempting to directly
access these devices too, as if the array controller were merely a SCSI
controller in the same way that we are allowing it to access SCSI tape drives.
SCSI error handling for tape drives and medium changers
-------------------------------------------------------
The linux SCSI mid layer provides an error handling protocol which
kicks into gear whenever a SCSI command fails to complete within a
certain amount of time (which can vary depending on the command).
The cciss driver participates in this protocol to some extent. The
normal protocol is a four step process. First the device is told
to abort the command. If that doesn't work, the device is reset.
If that doesn't work, the SCSI bus is reset. If that doesn't work
the host bus adapter is reset. Because the cciss driver is a block
driver as well as a SCSI driver and only the tape drives and medium
changers are presented to the SCSI mid layer, and unlike more
straightforward SCSI drivers, disk i/o continues through the block
side during the SCSI error recovery process, the cciss driver only
implements the first two of these actions, aborting the command, and
resetting the device. Additionally, most tape drives will not oblige
in aborting commands, and sometimes it appears they will not even
obey a reset coommand, though in most circumstances they will. In
the case that the command cannot be aborted and the device cannot be
reset, the device will be set offline.
In the event the error handling code is triggered and a tape drive is
successfully reset or the tardy command is successfully aborted, the
tape drive may still not allow i/o to continue until some command
is issued which positions the tape to a known position. Typically you
must rewind the tape (by issuing "mt -f /dev/st0 rewind" for example)
before i/o can proceed again to a tape drive which was reset.