Commit 6a0bdffa authored by Alan Stern's avatar Alan Stern Committed by Greg Kroah-Hartman

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: default avatarAlan Stern <>
Acked-by: default avatarHans de Goede <>
CC: "James E.J. Bottomley" <>
CC: Matthew Dharm <>
Cc: stable <>
Signed-off-by: default avatarGreg Kroah-Hartman <>
parent 1e2c4e59
......@@ -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))
......@@ -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;
......@@ -151,6 +151,7 @@ struct scsi_device {
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 */
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment