Re: [PATCH] bdev: add back PAGE_SIZE block size validation for sb_set_blocksize()

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Mar 05, 2025 at 06:04:21AM +0000, Matthew Wilcox wrote:
> On Tue, Mar 04, 2025 at 05:53:01PM -0800, Luis Chamberlain wrote:
> > The commit titled "block/bdev: lift block size restrictions to 64k"
> > lifted the block layer's max supported block size to 64k inside the
> > helper blk_validate_block_size() now that we support large folios.
> > However in lifting the block size we also removed the silly use
> > cases many filesystems have to use sb_set_blocksize() to *verify*
> > that the block size < PAGE_SIZE. The call to sb_set_blocksize() can
> > happen in-kernel given mkfs utilities *can* create for example an
> > ext4 32k block size filesystem on x86_64, the issue we want to prevent
> > is mounting it on x86_64 unless the filesystem supports LBS.
> > 
> > While, we could argue that such checks should be filesystem specific,
> > there are much more users of sb_set_blocksize() than LBS enabled
> > filesystem on linux-next, so just do the easier thing and bring back
> > the PAGE_SIZE check for sb_set_blocksize() users.
> > 
> > This will ensure that tests such as generic/466 when run in a loop
> > against say, ext4, won't try to try to actually mount a filesystem with
> > a block size larger than your filesystem supports given your PAGE_SIZE
> > and in the worst case crash.
> 
> So this is expedient because XFS happens to not call sb_set_blocksize()?
> What is the path forward for filesystems which call sb_set_blocksize()
> today and want to support LBS in future?

Well they /could/ set sb_blocksize/sb_blocksize_bits themselves, like
XFS does.

Luis: Is the bsize > PAGE_SIZE constraint in set_blocksize go away?
IOWs, will xfs support sector sizes > 4k in the near future?

--D