Subject: letting userland issue FUA writes
To: None <>
From: Bill Studenmund <>
List: tech-kern
Date: 03/14/2006 18:35:46
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I'm interested in adding infrastructure so that applications can issue=20
writes that have the FUA (Force Unit Access) bit set. SCSI CDBs handle=20
this, as do some RAID cards.

The main question I have is what kind of user-level interfaces exist for=20
this? I certainly could cook up a new system call, but I would much rather=
use prior art. My simplistic attempt at googling for this failed. Does=20
anyone else have suggestions?

Given the systemcall interface, driving it through the kernel isn't hard.=
A flag here and a flag there, and it's set.

The only other key question I see is what do we do with a driver that=20
doesn't natively handle FUA? My instinct is to error-out the command, as=20
that is what will happen if you use FUA to a SCSI disk that doesn't=20
support it. The sub-question is should the driver do it, which means every=
driver needs to catch this flag, or should we expose some sort of=20
capability and let some higher level of the queuing/processing system=20
catch the error.

Take care,


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