Re: [PATCH xfstests v2 2/2] open_by_handle: add tests for u64 mount ID

[Amir Goldstein]

On Mon, Sep 2, 2024 at 6:46 PM Aleksa Sarai <cyphar@xxxxxxxxxx> wrote:
>
> Now that open_by_handle_at(2) can return u64 mount IDs, do some tests to
> make sure they match properly as part of the regular open_by_handle
> tests.
>
> Link: https://lore.kernel.org/all/20240828-exportfs-u64-mount-id-v3-0-10c2c4c16708@xxxxxxxxxx/
> Signed-off-by: Aleksa Sarai <cyphar@xxxxxxxxxx>
> ---
> v2:
> - Remove -M argument and always do the mount ID tests. [Amir Goldstein]
> - Do not error out if the kernel doesn't support STATX_MNT_ID_UNIQUE
>   or AT_HANDLE_MNT_ID_UNIQUE. [Amir Goldstein]
> - v1: <https://lore.kernel.org/all/20240828103706.2393267-1-cyphar@xxxxxxxxxx/>
>
>  src/open_by_handle.c | 128 +++++++++++++++++++++++++++++++++----------
>  1 file changed, 99 insertions(+), 29 deletions(-)
>
> diff --git a/src/open_by_handle.c b/src/open_by_handle.c
> index d9c802ca9bd1..0ad591da632e 100644
> --- a/src/open_by_handle.c
> +++ b/src/open_by_handle.c
> @@ -86,10 +86,16 @@ Examples:
>  #include <errno.h>
>  #include <linux/limits.h>
>  #include <libgen.h>
> +#include <stdint.h>
> +#include <stdbool.h>
>
>  #include <sys/stat.h>
>  #include "statx.h"
>
> +#ifndef AT_HANDLE_MNT_ID_UNIQUE
> +#      define AT_HANDLE_MNT_ID_UNIQUE 0x001
> +#endif
> +
>  #define MAXFILES 1024
>
>  struct handle {
> @@ -120,6 +126,94 @@ void usage(void)
>         exit(EXIT_FAILURE);
>  }
>
> +int do_name_to_handle_at(const char *fname, struct file_handle *fh, int bufsz)
> +{
> +       int ret;
> +       int mntid_short;
> +
> +       static bool skip_mntid_unique;
> +
> +       uint64_t statx_mntid_short = 0, statx_mntid_unique = 0;
> +       struct statx statxbuf;
> +
> +       /* Get both the short and unique mount id. */
> +       if (statx(AT_FDCWD, fname, 0, STATX_MNT_ID, &statxbuf) < 0) {

This fails build on top of latest for-next branch with commit
873e36c9 - statx.h: update to latest kernel UAPI

It can be fixed by changing to use the private xfstests_statx()
implementation, same as in stat_test.c.

I am not sure how elegant this is, but that's the easy fix.

> +               fprintf(stderr, "%s: statx(STATX_MNT_ID): %m\n", fname);
> +               return EXIT_FAILURE;
> +       }
> +       if (!(statxbuf.stx_mask & STATX_MNT_ID)) {
> +               fprintf(stderr, "%s: no STATX_MNT_ID in stx_mask\n", fname);
> +               return EXIT_FAILURE;
> +       }
> +       statx_mntid_short = statxbuf.stx_mnt_id;
> +
> +       if (!skip_mntid_unique) {
> +               if (statx(AT_FDCWD, fname, 0, STATX_MNT_ID_UNIQUE, &statxbuf) < 0) {
> +                       fprintf(stderr, "%s: statx(STATX_MNT_ID_UNIQUE): %m\n", fname);
> +                       return EXIT_FAILURE;
> +               }
> +               /*
> +                * STATX_MNT_ID_UNIQUE was added fairly recently in Linux 6.8, so if the
> +                * kernel doesn't give us a unique mount ID just skip it.
> +                */
> +               if ((skip_mntid_unique |= !(statxbuf.stx_mask & STATX_MNT_ID_UNIQUE)))
> +                       printf("statx(STATX_MNT_ID_UNIQUE) not supported by running kernel -- skipping unique mount ID test\n");

This verbose print breaks all existing "exportfs" tests which do not
expect it in the golden output.

I understand that silently ignoring the failure is not good, but I also
would like to add this test coverage to all the existing tests.

One solution is to resurrect the command line option -M from v1,
but instead of meaning "test unique mount id" let it mean
"do not allow to skip unique mount id" test.

Then you can add a new test that runs open_by_handle -M, but also
implement a helper _require_unique_mntid similar to _require_btime
which is needed for the new test to run only on new kernels.

I'm sorry for this complication, but fstest is a testsuite that runs on
disto and stable kernels as well and we need to allow test coverage
of new features along with stability of the test env.

Thanks,
Amir.