Re: request for test with your quirky drive enclosure

Am Mittwoch, 31. Januar 2007 17:22 schrieb Alan Stern:
> On Wed, 31 Jan 2007, Oliver Neukum wrote:

> If some other device ends up needing this in the future, what makes you 
> think the heuristic you have chosen will be appropriate?

I've checked my disks and asked for counterexamples.
If you have a better heuristics, please tell me. It is derived
from the informal "rules" of pseudo CHS.
 
> > +	/* Some devices have version which report the correct sizes
> > +	 * and others which do not. We guess size according toa heuristic
> > +	 * and err on the side of lowering the capacity. */
> > +	if (sdp->guess_capacity)
> 
> The patch doesn't define sdp->guess_capacity anywhere.

This is the second time today. I need a notebook. Corrected version included.

> > +		if (sdkp->capacity % 63 || sdkp->capacity % 255)
> > +			--sdkp->capacity;
> 
> This is a strange computation.  You avoid decrementing the capacity iff it
> is already divisible both by 63 and by 255.  Maybe you really want to use
> && rather than || ?  The idea being, I presume, that the last partition
> will extend only as far as a pseudo-cylinder boundary.

Yes, but I am conservative. When in doubt, decrement.
This patch is a result of despair, I am running out of solutions.

	Regards
		Oliver
----

--- a/drivers/usb/storage/unusual_devs.h	2007-01-31 14:48:08.000000000 +0100
+++ b/drivers/usb/storage/unusual_devs.h	2007-01-31 15:37:40.000000000 +0100
@@ -1323,7 +1323,7 @@
 		"DataStor",
 		"USB4500 FW1.04",
 		US_SC_DEVICE, US_PR_DEVICE, NULL,
-		US_FL_FIX_CAPACITY),
+		US_FL_CAPACITY_HEURISTICS),
 
 /* Control/Bulk transport for all SubClass values */
 USUAL_DEV(US_SC_RBC, US_PR_CB, USB_US_TYPE_STOR),
--- a/drivers/usb/storage/scsiglue.c	2007-01-31 14:56:36.000000000 +0100
+++ b/drivers/usb/storage/scsiglue.c	2007-01-31 15:37:35.000000000 +0100
@@ -155,6 +155,12 @@
 		if (us->flags & US_FL_FIX_CAPACITY)
 			sdev->fix_capacity = 1;
 
+		/* A few disks have two indistinguishable version, one of
+		 * which reports the correct capacity and the other does not.
+		 * The sd driver has to guess which is the case. */
+		if (us->flags & US_FL_CAPACITY_HEURISTICS)
+			sdev->guess_capacity = 1;
+
 		/* Some devices report a SCSI revision level above 2 but are
 		 * unable to handle the REPORT LUNS command (for which
 		 * support is mandatory at level 3).  Since we already have
--- a/drivers/scsi/sd.c	2007-01-31 15:33:57.000000000 +0100
+++ b/drivers/scsi/sd.c	2007-01-31 15:37:52.000000000 +0100
@@ -1274,6 +1274,13 @@
 	if (sdp->fix_capacity)
 		--sdkp->capacity;
 
+	/* Some devices have version which report the correct sizes
+	 * and others which do not. We guess size according toa heuristic
+	 * and err on the side of lowering the capacity. */
+	if (sdp->guess_capacity)
+		if (sdkp->capacity % 63 || sdkp->capacity % 255)
+			--sdkp->capacity;
+
 got_data:
 	if (sector_size == 0) {
 		sector_size = 512;
--- a/include/linux/usb_usual.h	2007-01-31 14:49:55.000000000 +0100
+++ b/include/linux/usb_usual.h	2007-01-31 15:37:49.000000000 +0100
@@ -46,7 +46,9 @@
 	US_FLAG(MAX_SECTORS_64,	0x00000400)			\
 		/* Sets max_sectors to 64    */			\
 	US_FLAG(IGNORE_DEVICE,	0x00000800)			\
-		/* Don't claim device */
+		/* Don't claim device */			\
+	US_FLAG(CAPACITY_HEURISTICS,	0x00001000)		\
+		/* sometimes sizes is too big */
 
 #define US_FLAG(name, value)	US_FL_##name = value ,
 enum { US_DO_ALL_FLAGS };
--- a/include/scsi/scsi_device.h	2007-01-31 15:17:30.000000000 +0100
+++ b/include/scsi/scsi_device.h	2007-01-31 15:37:55.000000000 +0100
@@ -122,6 +122,7 @@
 	unsigned no_uld_attach:1; /* disable connecting to upper level drivers */
 	unsigned select_no_atn:1;
 	unsigned fix_capacity:1;	/* READ_CAPACITY is too high by 1 */
+	unsigned guess_capacity:1;	/* READ_CAPACITY might be too high by 1 */
 	unsigned retry_hwerror:1;	/* Retry HARDWARE_ERROR */
 
 	unsigned int device_blocked;	/* Device returned QUEUE_FULL. */

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