linux-kernel - Re: 2.a.30-rc7: fat filesystem misdetected as amiga

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Message-ID: <Pine.LNX.4.44L0.0905260958400.3584-100000@iolanthe.rowland.org>
Date:	Tue, 26 May 2009 10:04:01 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Michael S. Tsirkin" <mst@...hat.com>
cc:	Kay Sievers <kay.sievers@...y.org>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>
Subject: Re: 2.a.30-rc7: fat filesystem misdetected as amiga

On Tue, 26 May 2009, Michael S. Tsirkin wrote:

> On Mon, May 25, 2009 at 05:08:12PM -0400, Alan Stern wrote:
> > On Mon, 25 May 2009, Michael S. Tsirkin wrote:
> > 
> > > > So apparently this is a bug in the device; it doesn't respond correctly
> > > > to the first READ command.  But since it does respond correctly to 
> > > > later commands, everything works okay thereafter.  You ought to be able 
> > > > to recover from the error by running
> > > > 
> > > > 	blockdev --rereadpt /dev/sdb
> > > > 
> > > > manually.
> > > 
> > > Yes, this helps.
> > > Would it make sense for kernel to retry automatically?
> > > Why doesn't it?
> > 
> > I don't know the details in this case.  Most likely the error code 
> > (Logical Block Address Out of Range) is interpreted as a fatal 
> > non-retryable error.  For other sorts of errors, the kernel does retry.
> 
> Who would know? The scsi crowd?

They would know.  But it's easy enough to find out.  (Looks through 
the SCSI code...)  Here we go.  scsi_io_completion() contains this:

		case ILLEGAL_REQUEST:
			/* If we had an ILLEGAL REQUEST returned, then
			 * we may have performed an unsupported
			 * command.  The only thing this should be
			 * would be a ten byte read where only a six
			 * byte read was supported.  Also, on a system
			 * where READ CAPACITY failed, we may have
			 * read past the end of the disk.
			 */
			if ((cmd->device->use_10_for_rw &&
			    sshdr.asc == 0x20 && sshdr.ascq == 0x00) &&
			    (cmd->cmnd[0] == READ_10 ||
			     cmd->cmnd[0] == WRITE_10)) {
				/* This will issue a new 6-byte command. */
				cmd->device->use_10_for_rw = 0;
				action = ACTION_REPREP;
			} else if (sshdr.asc == 0x10) /* DIX */ {
				description = "Host Data Integrity Failure";
				action = ACTION_FAIL;
				error = -EILSEQ;
			} else
				action = ACTION_FAIL;
			break;

Since the Sense Key value was ILLEGAL_REQUEST and the ASC value wasn't 
0x10 or 0x20, action gets set to ACTION_FAIL.  Hence the command is not 
retried.

In the end, there's a limit to how far the kernel should go in 
compensating for buggy devices.  Your device may well have passed that 
limit.

Alan Stern

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