It's a hard thing to implement, in general, for scalability reasons.
To make it work, you need to examine each driver's error handling to
figure out what "fail fast" really means.
Most storage drivers are written to try as hard as possible to complete
a request, where "try as hard as possible" can often mean internal
retries while trying various multi-path configurations and hardware mode
changes. You might be catching SATA in the middle of error handling,
for example.
So each driver really has a /slight different/ version of "try to
complete this request", which has the obvious effects on BIO_RW_FAILFAST.
No clue about DASD, but in SATA's case I bet that a media or transfer
error could be returned to the system more rapidly, while we continue to
try to recover in the background. libata doesn't have any direct
knowledge of fail-fast at this point, IIRC.
But overall it's a job where you must examine each driver, or set of
drivers :/
Jeff
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