[PATCH 1/4] block: add a hard-readonly flag to struct gendisk

[Christoph Hellwig]

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 is used to set a whole-disk device read-only, any
   partitions will end up in a read-only state until the user
   explicitly clears the flag.

 - 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 at oracle.com>.

Reported-by: Oleksii Kurochko <olkuroch at cisco.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201221
Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 block/blk-core.c        |  2 +-
 block/genhd.c           | 34 +++++++++++++++++++---------------
 block/partitions/core.c |  3 +--
 include/linux/genhd.h   |  6 ++++--
 4 files changed, 25 insertions(+), 20 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index cee568389b7e11..0763d1eb85ce15 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -695,7 +695,7 @@ static inline bool bio_check_ro(struct bio *bio, struct block_device *part)
 {
 	const int op = bio_op(bio);
 
-	if (part->bd_read_only && op_is_write(op)) {
+	if (op_is_write(op) && bdev_read_only(part)) {
 		char b[BDEVNAME_SIZE];
 
 		if (op_is_flush(bio->bi_opf) && !bio_sectors(bio))
diff --git a/block/genhd.c b/block/genhd.c
index 565cf36a5f1864..5e746223b6fa0f 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1625,31 +1625,35 @@ static void set_disk_ro_uevent(struct gendisk *gd, int ro)
 	kobject_uevent_env(&disk_to_dev(gd)->kobj, KOBJ_CHANGE, envp);
 }
 
-void set_disk_ro(struct gendisk *disk, int flag)
+/**
+ * set_disk_ro - set a gendisk read-only
+ * @disk:	The disk device
+ * @state:	true or false
+ *
+ * This function is used to indicate whether a given disk device should have its
+ * read-only flag set. set_disk_ro() is typically used by device drivers to
+ * indicate whether the underlying physical device is write-protected.
+ */
+void set_disk_ro(struct gendisk *disk, bool read_only)
 {
-	struct disk_part_iter piter;
-	struct block_device *part;
-
-	if (disk->part0->bd_read_only != flag) {
-		set_disk_ro_uevent(disk, flag);
-		disk->part0->bd_read_only = flag;
+	if (read_only) {
+		if (test_and_set_bit(GD_READ_ONLY, &disk->state))
+			return;
+	} else {
+		if (!test_and_clear_bit(GD_READ_ONLY, &disk->state))
+			return;
 	}
-
-	disk_part_iter_init(&piter, disk, DISK_PITER_INCL_EMPTY);
-	while ((part = disk_part_iter_next(&piter)))
-		part->bd_read_only = flag;
-	disk_part_iter_exit(&piter);
+	set_disk_ro_uevent(disk, read_only);
 }
-
 EXPORT_SYMBOL(set_disk_ro);
 
 int bdev_read_only(struct block_device *bdev)
 {
 	if (!bdev)
 		return 0;
-	return bdev->bd_read_only;
+	return bdev->bd_read_only ||
+		test_bit(GD_READ_ONLY, &bdev->bd_disk->state);
 }
-
 EXPORT_SYMBOL(bdev_read_only);
 
 /*
diff --git a/block/partitions/core.c b/block/partitions/core.c
index deca253583bd3f..5a9633183343c0 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -194,7 +194,7 @@ 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,
@@ -360,7 +360,6 @@ 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;
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 809aaa32d53cba..a62ccbfac54b48 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -163,6 +163,7 @@ struct gendisk {
 	int flags;
 	unsigned long state;
 #define GD_NEED_PART_SCAN		0
+#define GD_READ_ONLY			1
 	struct kobject *slave_dir;
 
 	struct timer_rand_state *random;
@@ -249,11 +250,12 @@ static inline void add_disk_no_queue_reg(struct gendisk *disk)
 extern void del_gendisk(struct gendisk *gp);
 extern struct block_device *bdget_disk(struct gendisk *disk, int partno);
 
-extern void set_disk_ro(struct gendisk *disk, int flag);
+void set_disk_ro(struct gendisk *disk, bool read_only);
 
 static inline int get_disk_ro(struct gendisk *disk)
 {
-	return disk->part0->bd_read_only;
+	return disk->part0->bd_read_only ||
+		test_bit(GD_READ_ONLY, &disk->state);
 }
 
 extern void disk_block_events(struct gendisk *disk);
-- 
2.29.2