Re: removable device: can't detect disk changes

[Giuliano Pochini <pochini@shiny.it>]

On Mon, 18 Aug 2008 15:58:14 -0500
James Bottomley <James.Bottomley@HansenPartnership.com> wrote:

> On Mon, 2008-08-18 at 21:52 +0200, Giuliano Pochini wrote:
> > On Tue, 12 Aug 2008 15:08:14 +0200
> > Giuliano Pochini <pochini@shiny.it> wrote:
> > 
> > > 
> > > Fujitsu magneto-optical drive, Adaptec 29160 and 
> > > Linux Jay 2.6.26 #7 SMP Sun Aug 10 18:34:22 CEST 2008 ppc 7455, altivec supported PowerMac3,6 GNU/Linux
> > > 
> > > When I insert a disk and I mount it, scsi_test_unit_ready() is called and
> > > the do-while loop gets sshdr->sense_key == UNIT_ATTENTION in the first
> > > cycle and 0 in the second one. So the if below misses the UNIT_ATTENTION
> > > and sdev->changed = 1 is not executed. At this point bad things can
> > > happen... I'm not sure how to fix this. Any clue ?
> > 
> > Ok... what about this patch ?  The while() condition also checks for
> > NOT_READY. For removable devices sdev->changed is set when not_ready is
> > detected (not only if it occurs in the last cycle).
> > If works fine here, but since I don't know the SCSI subsystem this patch
> > may be wrong.
> 
> Well done! Almost ... apparently what needs to happen is what we're
> currently doing in sr_test_unit_ready.  There's no need to keep checking
> for NOT_READY ... that isn't a volatile condition like UNIT ATTENTION
> and driver_byte(result) & DRIVER_SENSE is equivalent to
> scsi_sense_valid(sshdr) in most cases.  Also, the while loop should exit
> on a non-UNIT ATTENTION condition (like NOT READY).
>
> Does this work?

> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
[...]

Yes, it works fine. This is your patch without the check for sshdr!=NULL
because it is already in scsi_sense_valid().


--- drivers/scsi/scsi_lib.c__orig	2008-08-18 21:11:45.000000000 +0200
+++ drivers/scsi/scsi_lib.c	2008-08-19 22:31:41.000000000 +0200
@@ -1972,22 +1972,21 @@ scsi_test_unit_ready(struct scsi_device 
 	do {
 		result = scsi_execute_req(sdev, cmd, DMA_NONE, NULL, 0, sshdr,
 					  timeout, retries);
-	} while ((driver_byte(result) & DRIVER_SENSE) &&
-		 sshdr && sshdr->sense_key == UNIT_ATTENTION &&
-		 --retries);
+		if (sdev->removable && scsi_sense_valid(sshdr) &&
+		    sshdr->sense_key == UNIT_ATTENTION)
+			sdev->changed = 1;
+	} while (scsi_sense_valid(sshdr) &&
+		 sshdr->sense_key == UNIT_ATTENTION && --retries);
 
 	if (!sshdr)
 		/* could not allocate sense buffer, so can't process it */
 		return result;
 
-	if ((driver_byte(result) & DRIVER_SENSE) && sdev->removable) {
-
-		if ((scsi_sense_valid(sshdr)) &&
-		    ((sshdr->sense_key == UNIT_ATTENTION) ||
-		     (sshdr->sense_key == NOT_READY))) {
-			sdev->changed = 1;
-			result = 0;
-		}
+	if (sdev->removable && scsi_sense_valid(sshdr) &&
+	    (sshdr->sense_key == UNIT_ATTENTION ||
+	     sshdr->sense_key == NOT_READY)) {
+		sdev->changed = 1;
+		result = 0;
 	}
 	if (!sshdr_external)
 		kfree(sshdr);



--
Giuliano.