Re: [LTP] [PATCH] statx09: Reduce fs-verity blocksize to 1024

[Petr Vorel <pvorel@suse.cz>]

Hi Eric, Martin,

Eric, thanks for your input, Martin, thanks for working on this.

> Hi Martin,

> On Thu, Jul 13, 2023 at 03:28:52PM +0200, Martin Doucha wrote:
> > The kernel requires that fs-verity blocksize must be at most equal
> > to the filesystem blocksize. Testing on small loop device means that
> > mkfs.ext4 will very likely default to blocksize of 1024. Set fs-verity
> > blocksize to the minimum possible value (1024) to avoid blocksize
> > mismatch.

Yes kernels < 6.3 TCONF on current master:
statx09.c:124: TCONF: fs-verity not supported on loopdev

And 6.3 fails:
statx09.c:109: TBROK: ioctl(3, FS_IOC_ENABLE_VERITY) failed: EINVAL (22)

> > Signed-off-by: Martin Doucha <mdoucha@suse.cz>
> > ---

> > Alternatively, we could add "-b 4096" to .dev_fs_opts.

> >  testcases/kernel/syscalls/statx/statx09.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)

> > diff --git a/testcases/kernel/syscalls/statx/statx09.c b/testcases/kernel/syscalls/statx/statx09.c
> > index c03d2c91e..dc9786c76 100644
> > --- a/testcases/kernel/syscalls/statx/statx09.c
> > +++ b/testcases/kernel/syscalls/statx/statx09.c
> > @@ -94,7 +94,7 @@ static void flag_setup(void)
> >  	memset(&enable, 0, sizeof(enable));
> >  	enable.version = 1;
> >  	enable.hash_algorithm = hash_algorithms[0];
> > -	enable.block_size = 4096;
> > +	enable.block_size = 1024;
> >  	enable.salt_size = 0;
> >  	enable.salt_ptr = (intptr_t)NULL;
> >  	enable.sig_size = 0;
> > -- 

> Support for Merkle tree block sizes less than the page size didn't exist until
> kernel version 6.3.  Please see the documentation for FS_IOC_ENABLE_VERITY
> (https://www.kernel.org/doc/html/latest/filesystems/fsverity.html#fs-ioc-enable-verity):

>     "block_size is the Merkle tree block size, in bytes. In Linux v6.3 and
>     later, this can be any power of 2 between (inclusively) 1024 and the minimum
>     of the system page size and the filesystem block size. In earlier versions,
>     the page size was the only allowed value."

> There are a few different approaches you could take.  One would be the one you
> mentioned: just add "-b 4096".  Though, note that systems with non-4K pages and
> kernel older than v6.3 can't mount an "-O verity -b 4096" filesystem.

I suppose the problem would be with e.g. ppc64le. Because otherwise
it works with this setup (untested on ppc64le, I believe it'd fail):
.dev_fs_opts = (const char *const []){"-O verity", "-b 4096", NULL},
and kept enable.block_size = 4096
the test passes on older kernels 6.2.12-1-default (openSUSE), 5.10.0-8-amd64
(Debian) as well as on 6.3 kernel.

> Or you could query the filesystem block size (that resulted from mkfs.ext4 with
> unspecified block size) and use that as the Merkle tree block size.

Unless it's not too complicated, it looks to me the best, as it'd support both
 >= 6.3 and older kernels.

> Or you could simply make the test depend on kernel v6.3, I suppose.

If possible I'd prefer to keep functionality also for older kernels.

Another (IMHO not really good option) would be to acquire device big enough via
.dev_min_size (it'd probably have to be too big device).

Kind regards,
Petr

> - Eric

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