This patch provides a sysfs interface allowing users to override the
capacity of a SCSI disk. This will help in situations where a buggy
USB-SATA adapter fails to support READ CAPACITY(16) and reports only
the low 32 bits of the capacity in its READ CAPACITY(10) reply. For
an example, see this thread:
http://marc.info/?l=linux-scsi&m=140908235510961&w=2
The interface is awkward because it requires the user to tell the
system to re-read the disk's partition table afterward, but at least
it provides a way to handle deficient hardware.
Signed-off-by: Alan Stern <[email protected]>
CC: Dale R. Worley <[email protected]>
---
[as1777]
Documentation/ABI/testing/sysfs-class-scsi_disk | 19 ++++++++++++
drivers/scsi/sd.c | 37 ++++++++++++++++++++++++
drivers/scsi/sd.h | 1
3 files changed, 57 insertions(+)
Index: usb-4.0/Documentation/ABI/testing/sysfs-class-scsi_disk
===================================================================
--- /dev/null
+++ usb-4.0/Documentation/ABI/testing/sysfs-class-scsi_disk
@@ -0,0 +1,19 @@
+What: /sys/class/scsi_disk/HOST:CHANNEL:TARGET:LUN/capacity_override
+Date: March 2015
+KernelVersion: 4.1
+Contact: Alan Stern <[email protected]>
+Description:
+ This file provides a way for users to override the
+ automatically determined disk capacity. For example, some
+ buggy USB-SATA adapters report only the low 32 bits of a
+ drive's block count, resulting in a calculated capacity
+ value that is the actual capacity modulo 2 TB.
+
+ After the correct capacity (in native-size blocks -- often
+ 512 bytes per block but sometimes 4096) is written to this
+ file, the user must tell the system to re-read the disk's
+ partition table by running the command:
+
+ /usr/sbin/blockdev --rereadpt /dev/sdX
+
+ where X is the disk's drive letter.
Index: usb-4.0/drivers/scsi/sd.h
===================================================================
--- usb-4.0.orig/drivers/scsi/sd.h
+++ usb-4.0/drivers/scsi/sd.h
@@ -66,6 +66,7 @@ struct scsi_disk {
struct gendisk *disk;
atomic_t openers;
sector_t capacity; /* size in 512-byte sectors */
+ sector_t capacity_override; /* in native-size blocks */
u32 max_xfer_blocks;
u32 max_ws_blocks;
u32 max_unmap_blocks;
Index: usb-4.0/drivers/scsi/sd.c
===================================================================
--- usb-4.0.orig/drivers/scsi/sd.c
+++ usb-4.0/drivers/scsi/sd.c
@@ -477,6 +477,35 @@ max_write_same_blocks_store(struct devic
}
static DEVICE_ATTR_RW(max_write_same_blocks);
+static ssize_t
+capacity_override_show(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ struct scsi_disk *sdkp = to_scsi_disk(dev);
+
+ return sprintf(buf, "%llu\n",
+ (unsigned long long) sdkp->capacity_override);
+}
+
+static ssize_t
+capacity_override_store(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct scsi_disk *sdkp = to_scsi_disk(dev);
+ unsigned long long cap;
+ int err;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EACCES;
+
+ err = kstrtoull(buf, 10, &cap);
+ if (err)
+ return err;
+ sdkp->capacity_override = cap;
+ return count;
+}
+static DEVICE_ATTR_RW(capacity_override);
+
static struct attribute *sd_disk_attrs[] = {
&dev_attr_cache_type.attr,
&dev_attr_FUA.attr,
@@ -489,6 +518,7 @@ static struct attribute *sd_disk_attrs[]
&dev_attr_provisioning_mode.attr,
&dev_attr_max_write_same_blocks.attr,
&dev_attr_max_medium_access_timeouts.attr,
+ &dev_attr_capacity_override.attr,
NULL,
};
ATTRIBUTE_GROUPS(sd_disk);
@@ -2152,6 +2182,13 @@ sd_read_capacity(struct scsi_disk *sdkp,
struct scsi_device *sdp = sdkp->device;
sector_t old_capacity = sdkp->capacity;
+ /* Did the user override the reported capacity? */
+ if (!sdkp->first_scan && sdkp->capacity_override) {
+ sector_size = sdkp->device->sector_size;
+ sdkp->capacity = sdkp->capacity_override;
+ goto got_data;
+ }
+
if (sd_try_rc16_first(sdp)) {
sector_size = read_capacity_16(sdkp, sdp, buffer);
if (sector_size == -EOVERFLOW)
--
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