[ 098/187] SCSI & usb-storage: add try_rc_10_first flag

Greg Kroah-Hartman
2012-07-12T23:30:45Z

From: Alan Stern <stern@rowland.harvard.edu>

commit 6a0bdffa0073857870a4ed1b4489762146359eb4 upstream.

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
09b6b51b0b6c1b9bb61815baf205e4d74c89ff04 (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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/scsi/sd.c | 2 ++
drivers/usb/storage/scsiglue.c | 6 ++++++
include/scsi/scsi_device.h | 1 +
3 files changed, 9 insertions(+)

--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1898,6 +1898,8 @@ static int sd_try_rc16_first(struct scsi
{
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))
--- a/drivers/usb/storage/scsiglue.c
+++ b/drivers/usb/storage/scsiglue.c
@@ -202,6 +202,12 @@ static int slave_configure(struct scsi_d
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;
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -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 */