On 11-12-19 08:11 AM, Paolo Bonzini wrote:
On 12/19/2011 01:22 PM, Hannes Reinecke wrote:
+ case VIRTIO_SCSI_S_UNDERRUN:
+ set_host_byte(sc, DID_ERROR);
+ break;
Hmm. Not sure this is correct.
UNDERRUN could be a valid state, eg it is quite common to send
an INQUIRY with a length of 255 bytes. And only evaluate the
bytes which are actually send back.
This happens when you send an INQUIRY with a sglist of 255 bytes and an
ALLOCATION LENGTH of 300 bytes. The spec says "VIRTIO_SCSI_S_UNDERRUN [is
returned] if the content of the CDB requires transferring more data than is
available in the data buffers".
Overrun! That is overrun.
Underrun conventionally refers to the data-in buffer
containing less data than the transport has allowed
for. It is detected at the completion of a SCSI command
and is used to report to the application client that
bytes beyond a certain position in the data-in buffer
are not valid (i.e. ignore them).
A mismatch between the allocation length field inside a
SCSI command (a difficult and dangerous area to snoop in)
and the data-in buffer length indicated by sglist should be
called something else. Arguably it should not be treated
as an error until an overrun occurs.
I think the 'case VIRTIO_SCSI_S_UNDERRUN:' line deserves a
comment due to its misleading use of the word "underrun".
It is reporting a potential or actual _overrun_.
Doug Gilbert
--
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
