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SubjectRe: For review: pidfd_send_signal(2) manual page
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On 9/23/19 1:31 PM, Daniel Colascione wrote:
> On Mon, Sep 23, 2019 at 2:12 AM Michael Kerrisk (man-pages)
> <mtk.manpages@gmail.com> wrote:
>> The pidfd_send_signal() system call allows the avoidance of race
>> conditions that occur when using traditional interfaces (such as
>> kill(2)) to signal a process. The problem is that the traditional
>> interfaces specify the target process via a process ID (PID), with
>> the result that the sender may accidentally send a signal to the
>> wrong process if the originally intended target process has termi‐
>> nated and its PID has been recycled for another process. By con‐
>> trast, a PID file descriptor is a stable reference to a specific
>> process; if that process terminates, then the file descriptor
>> ceases to be valid
>
> The file *descriptor* remains valid even after the process to which it
> refers exits. You can close(2) the file descriptor without getting
> EBADF. I'd say, instead, that "a PID file descriptor is a stable
> reference to a specific process; process-related operations on a PID
> file descriptor fail after that process exits".

Thanks, Daniel. I like that rephrasing, but, since pidfd_send_signal()
is (so far as I know) currently the only relevant process-related
operation (and because this is the manual page describing that
syscall), I made it:

[[
By contrast, a PID file descriptor is a stable reference to a
specific process; if that process terminates, pidfd_send_signal()
fails with the error ESRCH.
]]

Thanks,

Michael


--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

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