On Fri, 24 Aug 2007, Samuel Hangouët wrote:
> Hi,
>
> I'm currently using the driver g_file_storage on a gumstix product (see
> http://gumstix.org).
>
> This driver works fine when the option stall=N is set.
>
> However, I encountered a problem when I plug it in a JVC micro HiFi.
>
> With debug mode enabled, g_file_storage prints the following message in
> kernel log:
>
>
> g_file_storage gadget: bulk-out, length 31:
> 0: 55 53 42 43 03 00 00 00 12 00 00 00 80 00 05 03
> 10: 00 00 00 12 00 00 00 10 00 00 00 00 00 00 00
> g_file_storage gadget: non-meaningful CBW: lun = 0, flags = 0x80, cmdlen 5
>
> (see full log at the end of this email)
>
> In the command send by the HiFi equipment, the length of the CBWCB is
> equal to 5,
> which makes g_file_storage module reject the message in file_storage.c
> at line 3009 :
>
> /* Is the CBW meaningful? */
> if (cbw->Lun >= MAX_LUNS || cbw->Flags & ~USB_BULK_IN_FLAG ||
> cbw->Length < 6 || cbw->Length > MAX_COMMAND_SIZE) {
> DBG(fsg, "non-meaningful CBW: lun = %u, flags = 0x%x, "
> "cmdlen %u\n",
> cbw->Lun, cbw->Flags, cbw->Length);
>
> I wonder why there is a 6 in here.
>
> Indeed, the BBB Mass-Storage standard specifies:
>
> """
> bCBWCBLength:
> The valid length of the CBWCB in bytes. This defines the valid length
> of the command block. The
> only legal values are 1 through 16 (01h through 10h). All other
> values are reserved.
> """
You looked at the wrong part of the standard. 6.2.2 defines when the
CBW is meaningful; the third requirement is:
Both bCBWCBLength and the content of the CBWCB are in
accordance with bInterfaceSubClass.
In this case the relevant standard is SCSI SPC-2. It includes the
definition of the REQUEST SENSE command, and the definition says that
the command length is 6 bytes, not 5. In fact, none of the commands
accepted by g_file_storage have length < 6.
> and if I replaced this 6 by 1, everything works fine.
Really? It should failed this test in check_command():
/* Verify the length of the command itself */
if (cmnd_size != fsg->cmnd_size) {
/* Special case workaround: MS-Windows issues REQUEST SENSE
* with cbw->Length == 12 (it should be 6). */
if (fsg->cmnd[0] == SC_REQUEST_SENSE && fsg->cmnd_size == 12)
cmnd_size = fsg->cmnd_size;
else {
fsg->phase_error = 1;
return -EINVAL;
}
}
Here cmnd_size would be 6 and fsg->cmnd_size would be 5.
Alan Stern
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