pidfd: add ioctl to retrieve pid info

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A common pattern when using pid fds is having to get information
about the process, which currently requires /proc being mounted,
resolving the fd to a pid, and then do manual string parsing of
/proc/N/status and friends. This needs to be reimplemented over
and over in all userspace projects (e.g.: I have reimplemented
resolving in systemd, dbus, dbus-daemon, polkit so far), and
requires additional care in checking that the fd is still valid
after having parsed the data, to avoid races.

Having a programmatic API that can be used directly removes all
these requirements, including having /proc mounted.

As discussed at LPC24, add an ioctl with an extensible struct
so that more parameters can be added later if needed. Start with
returning pid/tgid/ppid and creds unconditionally, and cgroupid
optionally.

Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
Link: https://lore.kernel.org/r/20241010155401.2268522-1-luca.boccassi@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

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Luca Boccassi 2024-10-10 16:52:32 +01:00 • committed by Christian Brauner

parent 8e929cb546

commit cdda1f26e7

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3 changed files with 214 additions and 4 deletions

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86

fs/pidfs.c

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50

include/uapi/linux/pidfd.h

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82

tools/testing/selftests/pidfd/pidfd_open_test.c

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