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    • Linus Torvalds's avatar
      Merge tag 'pidfd-v5.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux · a9dce667
      Linus Torvalds authored
      Pull pidfd system call from Christian Brauner:
       "This introduces the ability to use file descriptors from /proc/<pid>/
        as stable handles on struct pid. Even if a pid is recycled the handle
        will not change. For a start these fds can be used to send signals to
        the processes they refer to.
      
        With the ability to use /proc/<pid> fds as stable handles on struct
        pid we can fix a long-standing issue where after a process has exited
        its pid can be reused by another process. If a caller sends a signal
        to a reused pid it will end up signaling the wrong process.
      
        With this patchset we enable a variety of use cases. One obvious
        example is that we can now safely delegate an important part of
        process management - sending signals - to processes other than the
        parent of a given process by sending file descriptors around via scm
        rights and not fearing that the given process will have been recycled
        in the meantime. It also allows for easy testing whether a given
        process is still alive or not by sending signal 0 to a pidfd which is
        quite handy.
      
        There has been some interest in this feature e.g. from systems
        management (systemd, glibc) and container managers. I have requested
        and gotten comments from glibc to make sure that this syscall is
        suitable for their needs as well. In the future I expect it to take on
        most other pid-based signal syscalls. But such features are left for
        the future once they are needed.
      
        This has been sitting in linux-next for quite a while and has not
        caused any issues. It comes with selftests which verify basic
        functionality and also test that a recycled pid cannot be signaled via
        a pidfd.
      
        Jon has written about a prior version of this patchset. It should
        cover the basic functionality since not a lot has changed since then:
      
            https://lwn.net/Articles/773459/
      
        The commit message for the syscall itself is extensively documenting
        the syscall, including it's functionality and extensibility"
      
      * tag 'pidfd-v5.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
        selftests: add tests for pidfd_send_signal()
        signal: add pidfd_send_signal() syscall
      a9dce667