Re: libata passthru: support PIO multi commands

From: Alan Cox
Date: Tue Jun 12 2007 - 12:00:30 EST

> ata_scsi_pass_thru() is not executed at ioctl submission time (block
> queue submission time), but rather immediately before it is issued to
> the drive. At that point you know the bus is idle, all other commands
> have finished executing, and dev->multi_count is fresh not stale. The
> code path goes from ata_scsi_pass_thru() to ata_qc_issue() without
> releasing the spinlock, even.

Think up to user space

Poorusersapp set multicount to 4

Evilproprietarytuningdaemon set multicount to 8

Poorusersapp issue I/O

at which point an error is indeed best.

> But the last point is true -- we should error rather than just warn
> there, AFAICS.

Definitely. We've been asked "please do something stupid" and not even in
a case where the requester may know better.

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