On 04/01/2014 11:36 PM, Vince Weaver wrote:
>
> The Linux 3.14 release adds support for the PERF_FLAG_FD_CLOEXEC flag to
> perf_event_open.2
>
> This version tries to clarify that the close-on-exec behavior applies to
> the current file descriptor being created.
>
> The wording is based on the description in kernel commit
> a21b0b354d4ac39be691f51c53562e2c24443d9e
> by Yann Droneaud <ydroneaud@xxxxxxxxxx>
Thanks, Vince.
I applied, and reworked the text to be:
PERF_FLAG_FD_CLOEXEC (since Linux 3.14).
This flag enables the close-on-exec flag for the created
event file descriptor, so that the file descriptor is
automatically closed on execve(2). Setting the close-
on-exec flags at creation time, rather than later with
fcntl(2), avoids potential race conditions where the
calling thread invokes perf_event_open() at the same
time as another thread calls fork(2) then execve(2).
Okay?
Cheers,
Michael
> Signed-off-by: Vince Weaver <vincent.weaver@xxxxxxxxx>
>
> diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
> index 30a2168..b4a49c4 100644
> --- a/man2/perf_event_open.2
> +++ b/man2/perf_event_open.2
> @@ -164,6 +164,19 @@ must be passed as the
> parameter.
> cgroup monitoring is available only
> for system-wide events and may therefore require extra permissions.
> +.TP
> +.BR PERF_FLAG_FD_CLOEXEC " (since Linux 3.14)."
> +This flag enables close-on-exec behavior for the created
> +event file descriptor, removing it from the list of
> +file descriptors inherited across exec.
> +Setting this behavior atomically at creation time rather than
> +later with
> +.BR fctl (2)
> +avoids potential race conditions between the current thread and
> +another calling
> +.BR fork (2)
> +then
> +.BR execve(2).
> .P
> The
> .I perf_event_attr
>
--
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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