diff mbox series

[4/6] block: propagate BLKROSET on the whole device to all partitions

Message ID 20210109104254.1077093-5-hch@lst.de
State New
Headers show
Series None | expand

Commit Message

Christoph Hellwig Jan. 9, 2021, 10:42 a.m. UTC
Change the policy so that a BLKROSET on the whole device also affects
partitions.  To quote Martin K. Petersen:

It's very common for database folks to twiddle the read-only state of
block devices and partitions. I know that our users will find it very
counter-intuitive that setting /dev/sda read-only won't prevent writes
to /dev/sda1.

The existing behavior is inconsistent in the sense that doing:

  # blockdev --setro /dev/sda
  # echo foo > /dev/sda1

permits writes. But:

  # blockdev --setro /dev/sda
  <something triggers revalidate>
  # echo foo > /dev/sda1

doesn't.

And a subsequent:

  # blockdev --setrw /dev/sda
  # echo foo > /dev/sda1

doesn't work either since sda1's read-only policy has been inherited
from the whole-disk device.

You need to do:

  # blockdev --rereadpt

after setting the whole-disk device rw to effectuate the same change on
the partitions, otherwise they are stuck being read-only indefinitely.

However, setting the read-only policy on a partition does *not* require
the revalidate step. As a matter of fact, doing the revalidate will blow
away the policy setting you just made.

So the user needs to take different actions depending on whether they
are trying to read-protect a whole-disk device or a partition. Despite
using the same ioctl. That is really confusing.

I have lost count how many times our customers have had data clobbered
because of ambiguity of the existing whole-disk device policy. The
current behavior violates the principle of least surprise by letting the
user think they write protected the whole disk when they actually
didn't.

Suggested-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
---
 block/genhd.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Comments

Hannes Reinecke Jan. 10, 2021, 3 p.m. UTC | #1
On 1/9/21 11:42 AM, Christoph Hellwig wrote:
> Change the policy so that a BLKROSET on the whole device also affects

> partitions.  To quote Martin K. Petersen:

> 

> It's very common for database folks to twiddle the read-only state of

> block devices and partitions. I know that our users will find it very

> counter-intuitive that setting /dev/sda read-only won't prevent writes

> to /dev/sda1.

> 

> The existing behavior is inconsistent in the sense that doing:

> 

>    # blockdev --setro /dev/sda

>    # echo foo > /dev/sda1

> 

> permits writes. But:

> 

>    # blockdev --setro /dev/sda

>    <something triggers revalidate>

>    # echo foo > /dev/sda1

> 

> doesn't.

> 

> And a subsequent:

> 

>    # blockdev --setrw /dev/sda

>    # echo foo > /dev/sda1

> 

> doesn't work either since sda1's read-only policy has been inherited

> from the whole-disk device.

> 

> You need to do:

> 

>    # blockdev --rereadpt

> 

> after setting the whole-disk device rw to effectuate the same change on

> the partitions, otherwise they are stuck being read-only indefinitely.

> 

> However, setting the read-only policy on a partition does *not* require

> the revalidate step. As a matter of fact, doing the revalidate will blow

> away the policy setting you just made.

> 

> So the user needs to take different actions depending on whether they

> are trying to read-protect a whole-disk device or a partition. Despite

> using the same ioctl. That is really confusing.

> 

> I have lost count how many times our customers have had data clobbered

> because of ambiguity of the existing whole-disk device policy. The

> current behavior violates the principle of least surprise by letting the

> user think they write protected the whole disk when they actually

> didn't.

> 

> Suggested-by: Martin K. Petersen <martin.petersen@oracle.com>

> Signed-off-by: Christoph Hellwig <hch@lst.de>

> Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>

> ---

>   block/genhd.c | 3 +--

>   1 file changed, 1 insertion(+), 2 deletions(-)

> 

Reviewed-by: Hannes Reinecke <hare@suse.de>


Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer
diff mbox series

Patch

diff --git a/block/genhd.c b/block/genhd.c
index e70bdc9b0893c1..10c76320510fef 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1658,8 +1658,7 @@  EXPORT_SYMBOL(set_disk_ro);
 
 int bdev_read_only(struct block_device *bdev)
 {
-	return bdev->bd_read_only ||
-		test_bit(GD_READ_ONLY, &bdev->bd_disk->state);
+	return bdev->bd_read_only || get_disk_ro(bdev->bd_disk);
 }
 EXPORT_SYMBOL(bdev_read_only);