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SubjectRe: [PATCH] queue barrier support
From said:
> ChangeSet@1.297, 2002-02-13 13:42:39+01:00,
> Add support for SCSI drivers to indicate support for ordered tags
> torvalds-2002020517305 \ 6-16047-c1d11a41ed024864/cset@
> index.html|ChangeSet@-1h

> ChangeSet@1.298, 2002-02-13 13:43:04+01:00,
> Add ordered tag support to the aic7xxx scsi driver

The rest of the aic7xxx code uses MSG_ORDERED_TASK rather than
MSG_ORDERED_Q_TAG. You have to scan through the headers to see that these are
#defined the same.

A problem (that is probably only an issue for older drives) is that while
technically the standard requires all 3 types of TAG to be supported if tag
queueing is, some drives really only have simple tag support in their
firmware, so you may need to add a blacklist for ordered tags on certain

A further issue is that you haven't added anything to the error recovery code
for this. If error recovery is activated for the device at the reset level,
all tags will be discarded by the device. The eh will retry the failing
command and then the other tagged commands will be re-issued from the
scsi_bottom_half_handler (assuming the low level device driver immediately
fails them with DID_RESET) in the order in which the low level driver failed
them. Thus you have potentially completely messed up the ordering when the
commands all get retried.

James Bottomley

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