Gerd Hoffmann wrote:
> On 11/26/09 11:57, Hannes Reinecke wrote:
>> Then the guest would see a partial request and retry the
>> remainder of the request, which (possibly after some iterations)
>> would result in all data transferred, albeit at a lower speed.
>
> Except they don't.
>
> /me looks at drivers/scsi/sd.c:sd_done()
>
> I can't see any sane way to tell linux that the request was too big.
>
residuals is the key:
drivers/scsi/scsi.c:scsi_finish_command()
good_bytes = scsi_bufflen(cmd);
if (cmd->request->cmd_type != REQ_TYPE_BLOCK_PC) {
int old_good_bytes = good_bytes;
drv = scsi_cmd_to_driver(cmd);
if (drv->done)
good_bytes = drv->done(cmd);
/*
* USB may not give sense identifying bad sector and
* simply return a residue instead, so subtract off the
* residue if drv->done() error processing indicates no
* change to the completion length.
*/
if (good_bytes == old_good_bytes)
good_bytes -= scsi_get_resid(cmd);
}
scsi_io_completion(cmd, good_bytes);
and in
drivers/scsi/scsi_lib.c:scsi_io_completion()
/*
* A number of bytes were successfully read. If there
* are leftovers and there is some kind of error
* (result != 0), retry the rest.
*/
if (scsi_end_request(cmd, error, good_bytes, result == 0) == NULL)
return;
No-one forces us to complete the _entire_ request; just completing
the request partially is perfectly okay as long as we mark it properly.
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
h...@suse.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)
