Re: [PATCH] block: Add config option to not allow writing to mounted devices

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jun 14, 2023 at 12:12:56PM +0200, Jan Kara wrote:
> Well, OK, I have not been precise :). Modifying a partition table (or LVM
> description block) is impossible to distinguish from clobbering a
> filesystem on open(2) time. Once we decide we implement arbitration of each
> individual write(2), we can obviously stop writes to area covered by some
> exclusively open partition. But then you are getting at the complexity
> level of tracking used ranges of block devices which Darrick has suggested
> and you didn't seem to like that (and neither do I).

Well, we track these ranges in the block_devices hanging off the gendisk
anyway, so this is a totally different league.  But in the end parsing
partition tables is a little easier than parsing file system metadata
but not fundamentally different.  So if we really want to lock down
broken sideband manipulations we can't allow that either and need
in-kernel support for manipulating partition tables if that is required
at run time.