Re: [Qemu-devel] [PATCH 1/2] atapi: abort transfers with 0 byte limits

[Kevin Wolf <kwolf@redhat.com>]

Am 11.07.2015 um 03:05 hat John Snow geschrieben:
> We're supposed to abort on transfers like this, unless we fill
> Word 125 of our IDENTIFY data with a default transfer size, which
> we don't currently do.
> 
> This is an ATA error, not a SCSI/ATAPI one.
> See ATA8-ACS3 sections 7.17.6.49 or 7.21.5.
> 
> If we don't do this, QEMU will loop forever trying to transfer
> zero bytes, which isn't particularly useful.
> 
> Signed-off-by: John Snow <jsnow@redhat.com>

Of course, one could argue that for a clean separation between the ATA
core and SCSI/ATAPI, this check should really be done in cmd_packet and
ide_abort_command() could stay static. And in fact, I do think it's
worthwhile to try getting a better separation in the mid term.

However, for a 2.4 fix, this patch might be the right thing to do.

The interesting part is that the SCSI command is already partially
handled before the error is returned. The required assumption here is
that the guest doesn't actually see any intermediate state between
issuing the command and getting the abort, so it doesn't notice that we
already started the command successfully. I _think_ that assumption
holds true.

Reviewed-by: Kevin Wolf <kwolf@redhat.com>