[PATCH 0/3] pidfd: add pidfd_prepare()

[Christian Brauner]

This adds the pidfd_prepare() helper which allows the caller to reserve
a pidfd number and allocates a new pidfd file that stashes the provided
struct pid.

This will allow us to remove places that either open code this
functionality e.g., during copy_process() or that currently call
pidfd_create() but then have to call close_fd() because there are still
failure points after pidfd_create() has been called.

Other functionality wants to make use of pidfd's as well and they need a
pidfd_prepare() internal api as well.

I've tested the fanotify and fork changes via LTP which provides
coverage for all the affected codepaths.

Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
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Christian Brauner (3):
      pid: add pidfd_prepare()
      fork: use pidfd_prepare()
      fanotify: use pidfd_prepare()

 fs/notify/fanotify/fanotify_user.c | 13 ++++---
 include/linux/pid.h                |  1 +
 kernel/fork.c                      | 12 +------
 kernel/pid.c                       | 69 +++++++++++++++++++++++++++++++-------
 4 files changed, 68 insertions(+), 27 deletions(-)
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base-commit: 197b6b60ae7bc51dd0814953c562833143b292aa
change-id: 20230327-pidfd-file-api-8b28d68cf0a9