Commit 6a0bdffa authored Jun 20, 2012 by Alan Stern Committed by Greg Kroah-Hartman Jun 22, 2012

SCSI & usb-storage: add try_rc_10_first flag



Several bug reports have been received recently for USB mass-storage
devices that don't handle READ CAPACITY(16) commands properly.  They
report bogus sizes, in some cases becoming unusable as a result.

The bugs were triggered by commit
09b6b51b (SCSI & usb-storage: add
flags for VPD pages and REPORT LUNS), which caused usb-storage to stop
overriding the SCSI level reported by devices.  By default, the sd
driver will try READ CAPACITY(16) first for any device whose level is
above SCSI_SPC_2.

It seems likely that any device large enough to require the use of
READ CAPACITY(16) (i.e., 2 TB or more) would be able to handle READ
CAPACITY(10) commands properly.  Indeed, I don't know of any devices
that don't handle READ CAPACITY(10) properly.

Therefore this patch (as1559) adds a new flag telling the sd driver
to try READ CAPACITY(10) before READ CAPACITY(16), and sets this flag
for every USB mass-storage device.  If a device really is larger than
2 TB, sd will fall back to READ CAPACITY(16) just as it used to.

This fixes Bugzilla #43391.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Hans de Goede <hdegoede@redhat.com>
CC: "James E.J. Bottomley" <JBottomley@parallels.com>
CC: Matthew Dharm <mdharm-usb@one-eyed-alien.net>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 1e2c4e59

drivers/scsi/sd.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -1899,6 +1899,8 @@ static int sd_try_rc16_first(struct scsi_device *sdp)
		{
		if (sdp->host->max_cmd_len < 16)
		return 0;
		if (sdp->try_rc_10_first)
		return 0;
		if (sdp->scsi_level > SCSI_SPC_2)
		return 1;
		if (scsi_device_protection(sdp))

drivers/usb/storage/scsiglue.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -202,6 +202,12 @@ static int slave_configure(struct scsi_device *sdev)
		if (us->fflags & US_FL_NO_READ_CAPACITY_16)
		sdev->no_read_capacity_16 = 1;

		/*
		* Many devices do not respond properly to READ_CAPACITY_16.
		* Tell the SCSI layer to try READ_CAPACITY_10 first.
		*/
		sdev->try_rc_10_first = 1;

		/* assume SPC3 or latter devices support sense size > 18 */
		if (sdev->scsi_level > SCSI_SPC_2)
		us->fflags \|= US_FL_SANE_SENSE;

include/scsi/scsi_device.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -151,6 +151,7 @@ struct scsi_device {
		SD_LAST_BUGGY_SECTORS */
		unsigned no_read_disc_info:1; /* Avoid READ_DISC_INFO cmds */
		unsigned no_read_capacity_16:1; /* Avoid READ_CAPACITY_16 cmds */
		unsigned try_rc_10_first:1; /* Try READ_CAPACACITY_10 first */
		unsigned is_visible:1; /* is the device visible in sysfs */

		DECLARE_BITMAP(supported_events, SDEV_EVT_MAXBITS); /* supported events */

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