[LTP] [PATCH v2] ioctl_loop06: update loopback block size validation

[Luis Chamberlain]

On Fri, Mar 14, 2025 at 10:24:52AM +0800, Li Wang wrote:
> Hi Luis,
> 
> On Fri, Mar 14, 2025 at 6:59 AM Luis Chamberlain <mcgrof@kernel.org> wrote:
> 
> > On Thu, Mar 13, 2025 at 05:24:45PM +0800, Li Wang wrote:
> > > The kernel commit 47dd6753 ("block/bdev: lift block size restrictions to
> > 64k")
> > > now supports block sizes larger than PAGE_SIZE, with a new upper limit of
> > > BLK_MAX_BLOCK_SIZE (64K). But ioctl_loop06 still assumes that PAGE_SIZE
> > is the
> > > maximum allowed block size, causing failures on newer kernels(>= 6.14):
> >
> 
> Well, this sounds like we need to go back to patch v1:
>   https://lists.linux.it/pipermail/ltp/2025-March/042599.html
> 
> Note: LTP has a function tst_kvercmp() for comparing kernel versions.

Close.

BLK_MAX_BLOCK_SIZE may change in the future so the only real way to
test for an invalid block size is having a check for linux/blkdev.h.

I see commit 7c84fa710f75 ("ioprio: use ioprio.h kernel header if it
exists") is an example of using a kernel header file. I think similar
thing can be done to use linux/blkdev.h and if you don't have
HAVE_LINUX_BLKDEV_H then you can define BLK_MAX_BLOCK_SIZE to 64k for
for older kernels.

A more appropriate invalid value would be BLK_MAX_BLOCK_SIZE * 2 as
non power of 2 values will be outright disallowed.

  Luis