Re: inquiry in scsi_scan.c

[Matthew Dharm <mdharm-kernel@one-eyed-alien.net>]

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Instead of fixing this in usb-storage, I think I would rather make
scsi_scan.c just assume a minimum of 36.

Or, put another way, if the first request indicates less than 36, why
should we do a second request?  We already have all the data...

Matt

On Sat, Jan 04, 2003 at 04:07:51AM +0100, Andries.Brouwer@cwi.nl wrote:
> Matthew Dharm writes:
> 
> > There should probably be a sanity check to never ask for INQUIRY
> > less than 36 bytes.  I thought there used to be such a thing....
> 
> As Doug also points out, we ask for 36, but there is no
> guarantee that we get what we ask for.
> 
> > Actually, 5 isn't minimal... it's sub-minimal.
> > That's an error in the INQUIRY data/
> > The minimum (by spec) is 36 bytes.
> 
> No. Quoting:
> 
> "The INQUIRY data (Table 7-9) contains a five byte header,
> followed by the vendor unique parameters, if any."
> (SCSI-1 standard)
> 
> So, as long as we are willing to support SCSI-1 devices,
> we must accept that the INQUIRY data can be as short as this.
> And in fact all our other code is careful - look at
> print_inquiry() how before looking at a byte we check
> whether it really there.
> 
> 
> On the other hand, my case was not an ancient SCSI-1 device,
> it was a brand new USB device. So, I have the SCSI host in hand.
> Looking at what happens:
> 
> usb-storage: usb_stor_bulk_transfer_buf(): xfer 36 bytes
>  00 80 00 00 00 00 00 00 4F 45 49 2D 55 53 42 20
>  53 6D 61 72 74 4D 65 64 69 61 20 20 20 20 20 20
>  32 2E 30 35
> usb-storage: Status code 0; transferred 36/36
> usb-storage: Fixing INQUIRY data to show SCSI rev 2 - was 0
> usb-storage: Fixing INQUIRY data to show length 36 - was 0
> 
> and all is fine.
> 
> Instead of the old garbage I now see:
> % cat /proc/scsi/scsi
> ...
> Host: scsi2 Channel: 00 Id: 00 Lun: 00
>   Vendor: OEI-USB  Model: SmartMedia       Rev: 2.05
>   Type:   Direct-Access                    ANSI SCSI revision: 02
> ...
> 
> 
> Conclusion:
> (i) scsi_scan.c has to be careful about INQUIRY lengths,
> and some patch is required for devices that return a short length.
> (ii) usb-storage knows the transport length, and can fix it
> in case it is (5+)0. For example, in protocol.c:fix_inquiry_data():
> 
> static void fix_inquiry_data(Scsi_Cmnd *srb)
> {
>         unsigned char *data_ptr;
> 
>         /* verify that it's an INQUIRY command */
>         if (srb->cmnd[0] != INQUIRY)
>                 return;
> 
>         data_ptr = find_data_location(srb);
> 
>         if ((data_ptr[2] & 7) != 2) {
>                 US_DEBUGP("Fixing INQUIRY data to show SCSI rev 2 - was %d\n",
>                           data_ptr[2] & 7);
> 
>                 /* Change the SCSI revision number */
>                 data_ptr[2] = (data_ptr[2] & ~7) | 2;
>         }
> 
>         if (data_ptr[4] == 0) {
>                 US_DEBUGP("Fixing INQUIRY data to show length 36 - was 0\n");
>                 data_ptr[4] = 36 - 5;
>         }
> }
> 
> Andries

-- 
Matthew Dharm                              Home: mdharm-usb@one-eyed-alien.net 
Maintainer, Linux USB Mass Storage Driver

It was a new hope.
					-- Dust Puppy
User Friendly, 12/25/1998

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