Hello Florian,
On 9/23/19 1:26 PM, Florian Weimer wrote:
> * Michael Kerrisk:
>
>> SYNOPSIS
>> int pidfd_send_signal(int pidfd, int sig, siginfo_t info,
>> unsigned int flags);
>
> This probably should reference a header for siginfo_t.
Thanks. I added: #include <signal.h>
>> ESRCH The target process does not exist.
>
> If the descriptor is valid, does this mean the process has been waited
> for? Maybe this can be made more explicit.
Yes. I added "(i.e., it has terminated and been waited on)".
>> 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 and the caller of pidfd_send_signal() is
>> informed of this fact via an ESRCH error.
>
> It would be nice to explain somewhere how you can avoid the race using
> a PID descriptor. Is there anything else besides CLONE_PIDFD?
Please see my comment in reply to Christian (which will be sent just
after this).
>> static
>> int pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
>> unsigned int flags)
>> {
>> return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
>> }
>
> Please use a different function name. Thanks.
Please see my open question in the thread on pidfd_open().
Thanks for the review, Florian.
Cheers,
Michael
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
