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

[Luis Chamberlain]

On Thu, Mar 13, 2025 at 10:52:31PM -0700, Luis Chamberlain wrote:
> 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.

While at it, be sure to scale tst_fill_file("test.img", 0, 1024, 1024)
(I think that is bs=1024, count=1024, so 1 MiB file size) so that you
take into consideration the BLK_MAX_BLOCK_SIZE so that the file size
will be at least maybe 10 * BLK_MAX_BLOCK_SIZE or something sensible.

Because as soon as we can support a BLK_MAX_BLOCK_SIZE of 2 MiB this
test will also fail again.

  Luis