[Bug libc/26371] [RFE] please add clone3() wrapper (in particular the CLONE_INTO_CGROUP feature of it)

["adhemerval.zanella at linaro dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=26371

Adhemerval Zanella <adhemerval.zanella at linaro dot org> changed:

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                 CC|                            |adhemerval.zanella at linaro dot o
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--- Comment #13 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> ---
(In reply to Luca Boccassi from comment #12)
> In systemd we are also interested in posix_spawn, but there's 3 features
> we'd need added:
> 
> 1) spawn-by-fd version that takes file descriptor instead of path
> 2) CLONE_INTO_CGROUP support
> 3) support for returning PID FD instead/together with PID
> 
> Is this something that would be possible to implement? Thanks!

I have been working on extending fork and posix_spawn to support PIDFD (BZ
30349) and I think these interfaces might be the way to provide
CLONE_INTO_CGROUP and/or any clone3 extension. These are Linux-specific and
provide wrapper over clone calls.

I added pidfd_fork in a way it can be a superset of both fork and _Fork, and it
should be simple to extend to get a new argument: if this has a non-negative
value it will pass CLONE_INTO_CGROUP along with the group file descriptor.  Now
that clone3 is an extensible interface, I wonder if glibc should also follow a
similar approach (mainly to avoid the need to keep adding versioned symbols for
any additional new clone3 support).

posix_spawn accomplishes it by using a posix_spawnattr_t along with
init/destroy interface and glibc implementation adds some slack space for
possible extensions. Maybe we can add similar support for pidfd_fork, so
instead of named arguments, it uses a sized struct with input/output values.

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