enforce read-only state at the block layer

[Christoph Hellwig <hch@lst.de>]

Hi all,

I've recently got a report where a file system can write to a read-only
block device, and while I've not found the root cause yet, it is very
clear that we should not prevents writes to read-only at all.

This did in fact get fixed 5 years ago, but Linus reverted it as older
lvm2 tools relying on this broken behavior.  This series tries to
restore it, although I'm still worried about thee older lvm2 tools
to be honest.  Question to the device mapper maintainers:  is the
any good way to work around that behavior in device mapper if needed
instead of leaving the core block layer and drivers exposed?

Diffstat:
 block/blk-core.c       |   20 ++++++++------------
 include/linux/blkdev.h |    1 -
 2 files changed, 8 insertions(+), 13 deletions(-)