[patch] perf_event_open.2 : document PERF_FLAG_FD_CLOEXEC flag

[patch] perf_event_open.2 : document PERF_FLAG_FD_CLOEXEC flag

[Vince Weaver]

The Linux 3.14 release adds support for the PERF_FLAG_FD_CLOEXEC flag to
perf_event_open.2

The wording is based on the description in kernel commit
a21b0b354d4ac39be691f51c53562e2c24443d9e 
by Yann Droneaud <ydroneaud-RlY5vtjFyJ3QT0dZR+AlfA@public.gmane.org>

Signed-off-by: Vince Weaver <vincent.weaver-e7X0jjDqjFGHXe+LvDLADg@public.gmane.org>

diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
index 30a2168..46cc204 100644
--- a/man2/perf_event_open.2
+++ b/man2/perf_event_open.2
@@ -164,6 +164,17 @@ 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 allows atomically setting close-on-exec behavior on
+a created event without needing to call
+.BR fcntl (2).
+This lets userspace remove the file descriptor from the list of
+file descriptors inherited across exec and avoid race conditions
+between the current thread and another calling
+.BR fork (2)
+then
+.BR execve (2).
 .P
 The
 .I perf_event_attr
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Re: [patch] perf_event_open.2 : document PERF_FLAG_FD_CLOEXEC flag

[Michael Kerrisk (man-pages)]

Hello Vince,

On 03/31/2014 09:40 PM, Vince Weaver wrote:
> 
> The Linux 3.14 release adds support for the PERF_FLAG_FD_CLOEXEC flag to
> perf_event_open.2

Thanks for the patch. However, I don't find it too clear.
Is this flag about setting the c-o-e flag for the file descriptor
returned as the return value of perf_event_open()? If so, I think
it needs to be worded more clearly to say that/ Could you take a 
look and resubmit?

Thanks,

Michael


> The wording is based on the description in kernel commit
> a21b0b354d4ac39be691f51c53562e2c24443d9e 
> by Yann Droneaud <ydroneaud-RlY5vtjFyJ3QT0dZR+AlfA@public.gmane.org>
> 
> Signed-off-by: Vince Weaver <vincent.weaver-e7X0jjDqjFGHXe+LvDLADg@public.gmane.org>
> 
> diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
> index 30a2168..46cc204 100644
> --- a/man2/perf_event_open.2
> +++ b/man2/perf_event_open.2
> @@ -164,6 +164,17 @@ 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 allows atomically setting close-on-exec behavior on
> +a created event without needing to call
> +.BR fcntl (2).
> +This lets userspace remove the file descriptor from the list of
> +file descriptors inherited across exec and avoid 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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