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 <stern@xxxxxxxxxxxxxxxxxxx> CC: Dale R. Worley <worley@xxxxxxxxxxxx> --- [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 <stern@xxxxxxxxxxxxxxxxxxx> +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) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
