[LTP] [PATCH] block: add BLK_FEAT_LBS to check for PAGE_SIZE limit

[Christoph Hellwig]

On Tue, Mar 11, 2025 at 10:00:28PM -0700, Luis Chamberlain wrote:
> We should take time to validate each block driver before enabling
> support for larger logical block sizes, so that those that didn't
> have support stay that way and don't need modifications.
> 
> Li Wang reported this as a regression on LTP via:
> 
> testcases/kernel/syscalls/ioctl/ioctl_loop06
> 
> Which uses the loopback driver to enable larger logical block sizes
> first with LOOP_CONFIGURE and then LOOP_SET_BLOCK_SIZE. While
> I see no reason why the loopback block driver can't support
> larger logical block sizes than PAGE_SIZE, leave this validation
> step as a secondary effort for each block driver.

This doesn't really make sense.  We don't want a flag that caps driver
controlled values at a arbitrary value (and then not used it at all in
the patch).

If you need extra per-driver validatation, do it in the driver.