Messages in this thread |  | | Date | Sat, 4 Jan 2003 16:41:13 -0800 | From | Matthew Dharm <> | Subject | Re: inquiry in scsi_scan.c |
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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 [unhandled content-type:application/pgp-signature] |  |