block: add a hard-readonly flag to struct gendisk

Commit 20bd1d026aac ("scsi: sd: Keep disk read-only when re-reading
partition") addressed a long-standing problem with user read-only
policy being overridden as a result of a device-initiated revalidate.
The commit has since been reverted due to a regression that left some
USB devices read-only indefinitely.

To fix the underlying problems with revalidate we need to keep track
of hardware state and user policy separately.

The gendisk has been updated to reflect the current hardware state set
by the device driver. This is done to allow returning the device to
the hardware state once the user clears the BLKROSET flag.

The resulting semantics are as follows:

 - If BLKROSET sets a given partition read-only, that partition will
   remain read-only even if the underlying storage stack initiates a
   revalidate. However, the BLKRRPART ioctl will cause the partition
   table to be dropped and any user policy on partitions will be lost.

 - If BLKROSET has not been set, both the whole disk device and any
   partitions will reflect the current write-protect state of the
   underlying device.

Based on a patch from Martin K. Petersen <martin.petersen@oracle.com>.

Reported-by: Oleksii Kurochko <olkuroch@cisco.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201221
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 1 insertions, 2 deletions

diff --git a/block/partitions/core.c b/block/partitions/core.c
index e7d776db803b..168d5906077c 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -195,7 +195,7 @@ static ssize_t part_start_show(struct device *dev,
 static ssize_t part_ro_show(struct device *dev,
 			    struct device_attribute *attr, char *buf)
 {
-	return sprintf(buf, "%d\n", dev_to_bdev(dev)->bd_read_only);
+	return sprintf(buf, "%d\n", bdev_read_only(dev_to_bdev(dev)));
 }
 
 static ssize_t part_alignment_offset_show(struct device *dev,
@@ -361,7 +361,6 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
 
 	bdev->bd_start_sect = start;
 	bdev_set_nr_sectors(bdev, len);
-	bdev->bd_read_only = get_disk_ro(disk);
 
 	if (info) {
 		err = -ENOMEM;