Re: [PATCH iproute2-next v3] lib/fs: fix issue when {name,open}_to_handle_at() is not implemented

[Petr Vorel <petr.vorel@gmail.com>]

Hi,

[ Cc Petr (Buildroot maintainer) ]
> With commit d5e6ee0dac64 the usage of functions name_to_handle_at() and
> open_by_handle_at() are introduced. But these function are not available
> e.g. in uclibc-ng < 1.0.35. To have a backward compatibility check for the
> availability in the configure script and in case of absence do a direct
> syscall.

> Fixes: d5e6ee0dac64 ("ss: introduce cgroup2 cache and helper functions")
> Cc: Dmitry Yakunin <zeil@yandex-team.ru>
> Cc: Petr Vorel <petr.vorel@gmail.com>
> Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>
> ---
> v3:
>  - use correct syscall number (thanks to Petr Vorel)
>  - add #include <sys/syscall.h> (thanks to Petr Vorel)
>  - remove bogus parameters (thanks to Petr Vorel)
>  - fix #ifdef (thanks to Petr Vorel)
>  - added Fixes tag (thanks to David Ahern)
>  - build test with buildroot 2020.08.3 using uclibc 1.0.34
I tested it to some extent. I was not able to test it on buildroot uclibc:
$ ss -a --cgroup # I put debugging printf
ss.c:3336 inet_show_sock(): tb[INET_DIAG_CGROUP_ID]: (nil), INET_DIAG_CGROUP_ID: 21

I tried mount both cgroup (with cgroupfs-mount) and cgroup2 (using mount).

But it's hard to trigger this code also on regular linux distro with glibc:

$ ss --cgroup -a >/dev/null
Failed to open cgroup2 by ID
Failed to open cgroup2 by ID
Failed to open cgroup2 by ID
Failed to open cgroup2 by ID
Failed to open cgroup2 by ID
Failed to open cgroup2 by ID

Debugging when replacing glibc wrapper with these functions calling raw syscall
it works the same (i.e. "Failed to open cgroup2 by ID")

Thus:
Tested-by: Petr Vorel <petr.vorel@gmail.com>
(to my previous Reviewed-by: tag).

Hope David Ahern send his patch for config.mk dependency to configure,
as his fragment [1] LGTM.

Kind regards,
Petr

[1] https://lore.kernel.org/netdev/82c9159f-0644-40af-fb4c-cc8507456719@gmail.com/