Kernel patch to work around deficiencies in usbmon

[Dave Jones]

On Sun, Jul 10, 2005 at 08:25:39PM -0700, Pete Zaitcev wrote:

Hey Pete,

 > We have usbmon enabled now and it's good, but usb-storage moved away
 > from under me a little bit. It now maps everything for DMA beforehand,
 > which makes usbmon to miss the SCSI commands and replies.
 > 
 > I am going to address this problem in usbmon, where it belongs, but
 > it requires some work which is not done.
 > 
 > What do you think about carrying the attached patch for a few months
 > (I hope to turn around sooner, but you know how that works!)

I'm puzzled (mostly due to my cluelessness in this area)..

 > @@ -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);

I assume this is being done to defeat the check..

    /* we assume that if transfer_buffer isn't us->iobuf then it
     * hasn't been mapped for DMA.  Yes, this is clunky, but it's
     * easier than always having the caller tell us whether the
     * transfer buffer has already been mapped. */
    us->current_urb->transfer_flags =
            URB_ASYNC_UNLINK | URB_NO_SETUP_DMA_MAP;

in usb_stor_msg_common()  ?

Is there any danger of the rest of the code that uses ->iobuf not being
aware that we're now starting 4 bytes in, and running past the end of the
buffer ?

 > @@ -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;
 >  	}

If ->iobuf is a ptr to 31 bytes, and bcb starts 4 bytes in, won't this
be writing to the 35th byte of iobuf ?

I'm probably missing something obvious, so hand me a dummys guide to
usb-storage hacking ;)

		Dave