On Wed, 05 Mar 2008 01:42:45 +0900
Tejun Heo <htejun@xxxxxxxxx> wrote:
> Tejun Heo wrote:
> > Tejun Heo wrote:
> >> FUJITA Tomonori wrote:
> >>>> Aiee... device going down after timing out on READ_DISC_INFO. That's
> >>>> gruesome. Can you please try the other patches?
> >>> Tejun, I thought that libata needs a fix for sum(sg) != rq->data_len. No?
> >> The extra_len you added to qc->nbytes should be it. The only other
> >> place to pay attention is the ATAPI transfer chunk size and your patch
> >> seems to get it right.
> >>
> >>> Now Jens' git tree should work with all the non libata stuff, ide,
> >>> firewire, bsg, etc. But I'm not sure about libata.
> >> With the second patch, all others should be fine no matter what. I'll
> >> go check libata part again.
> >
> > I can reproduce the problem here and it's very weird. I'll report back
> > when I know more.
>
> Okay, I got it. Heh, it turns out SCSI and/or block layer is not
> ready for rq->data_len != sum(sg). When adjusted command completes,
> SCSI midlayer completes the command with rq->data_len for PC commands
> which eventually ends up in __end_that_request_first(). As there are
> extra sg area left after completing rq->data_len, blk layer says so to
> SCSI layer and SCSI layer retries the command only with the appended
> area.
Ah, thanks!
> The following patch gets the writing going. I really think it's a
> serious mistake to break rq->data_len == sum(sg). If we break
> rq->data_len == requested size, the worst bugs are giving wrong size
> when issuing commands to application layer of devices which is
> relatively easy to spot and not all that command anyway. Breaking
> rq->data_len == sum(sg), bugs will be in internal mechanics, DMA
> engine programming and transport layer. Oh well...
>
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index fecba05..32439ac 100644
> --- a/drivers/scsi/scsi.c
> +++ b/drivers/scsi/scsi.c
> @@ -757,7 +757,7 @@ void scsi_finish_command(struct scsi_cmnd *cmd)
> "Notifying upper driver of completion "
> "(result %x)\n", cmd->result));
>
> - good_bytes = scsi_bufflen(cmd);
> + good_bytes = scsi_bufflen(cmd) + cmd->request->data_len;
> if (cmd->request->cmd_type != REQ_TYPE_BLOCK_PC) {
> drv = scsi_cmd_to_driver(cmd);
> if (drv->done)
>
>
Hmm, does SCSI mid-layer need to care about how many bytes the block
layer allocates? I don't think that extra_len is NOT good_bytes.
I think that the block layer had better take care about it (fix
__end_that_request_first?).
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