On Wed, 6 Jul 2005, Pete Zaitcev wrote:
> Hi, Guys:
>
> I'm thinking about carrying this patch in Fedora for the time being:
>
> diff -urp -X dontdiff linux-2.6.12/drivers/usb/storage/transport.c
> linux-2.6.12-lem/drivers/usb/storage/transport.c
> --- linux-2.6.12/drivers/usb/storage/transport.c 2005-06-21
> 12:58:48.000000000 -0700
> +++ linux-2.6.12-lem/drivers/usb/storage/transport.c 2005-07-06
> 14:00:30.000000000 -0700
> @@ -948,8 +948,9 @@ int usb_stor_Bulk_max_lun(struct us_data
>
> int usb_stor_Bulk_transport(struct scsi_cmnd *srb, struct us_data *us)
> {
> - struct bulk_cb_wrap *bcb = (struct bulk_cb_wrap *) us->iobuf;
> - struct bulk_cs_wrap *bcs = (struct bulk_cs_wrap *) us->iobuf;
> + /* Offset into iobuf a little in order to defeat pre-set DMA */
> + struct bulk_cb_wrap *bcb = (struct bulk_cb_wrap *) (us->iobuf + 4);
> + struct bulk_cs_wrap *bcs = (struct bulk_cs_wrap *) (us->iobuf + 4);
> unsigned int transfer_length = srb->request_bufflen;
> unsigned int residue;
> int result;
> @@ -960,7 +961,7 @@ int usb_stor_Bulk_transport(struct scsi_
> /* Take care of BULK32 devices; set extra byte to 0 */
> if ( unlikely(us->flags & US_FL_BULK32)) {
> cbwlen = 32;
> - us->iobuf[31] = 0;
> + ((unsigned char *)bcb)[31] = 0;
> }
>
> /* set up the command wrapper */
>
> I do not detect performance issues, although that says nothing.
> There may be some.
>
> Without it, the usbmon in 2.6.12 cannot capture SCSI commands.
> This ought to be fixed in usbmon, but it takes some time.
>
> Does anyone think that this is a very bad idea?
Performance issues would be highly platform-dependent. With x86 machines
there is practically no overhead to DMA mapping (as far as I know). What
about PPC or others?
In the end you will want to update usbmon to be able to read data, given
only the DMA mapping. For now, this seems like a reasonable substitute.
Alan Stern
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