Re: [PATCH v2] libselinux: use /proc/thread-self when available

[Eric Paris <eparis@redhat.com>]

Looks good to me.

That issue also brings up problems with glibc pid caching, right? Do we
need to rip out my *con cache entirely? I remember there was a
measurable perf win with the cache, but it has proved a PITA multiple
times. Keeping the cache and fixing/working around the glibc pid
caching would mean a tradeoff using getpid(2) instead of getpid(3),
even with this patch. Right? Or maybe storing a ctid instead of cpid
and using gettid(2)...

But this patch is LGTM.

On Mon, 2015-07-13 at 09:23 -0400, Stephen Smalley wrote:
> Linux 3.17 introduced a /proc/thread-self symlink that can be used
> to reference the proc files of the current thread without needing to
> use gettid(2).  Use this symlink when it exists, falling back to
> using gettid(2) when it does not.  This is generally beneficial, but
> was specifically motivated by 
> https://github.com/systemd/systemd/issues/475.
> 
> Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
> ---
> Only change is the patch description: /proc/thread-self was 
> introduced in
> Linux 3.17, not Linux 3.16.
> 
>  libselinux/src/procattr.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/libselinux/src/procattr.c b/libselinux/src/procattr.c
> index f990350..e444571 100644
> --- a/libselinux/src/procattr.c
> +++ b/libselinux/src/procattr.c
> @@ -95,6 +95,12 @@ static int openattr(pid_t pid, const char *attr, 
> int flags)
>  	if (pid > 0)
>  		rc = asprintf(&path, "/proc/%d/attr/%s", pid, attr);
>  	else {
> +		rc = asprintf(&path, "/proc/thread-self/attr/%s", 
> attr);
> +		if (rc < 0)
> +			return -1;
> +		fd = open(path, flags | O_CLOEXEC);
> +		if (fd >= 0 || errno != ENOENT)
> +			goto out;
>  		if (!tid)
>  			tid = gettid();
>  		rc = asprintf(&path, "/proc/self/task/%d/attr/%s", 
> tid, attr);
> @@ -103,6 +109,7 @@ static int openattr(pid_t pid, const char *attr, 
> int flags)
>  		return -1;
>  
>  	fd = open(path, flags | O_CLOEXEC);
> +out:
>  	free(path);
>  	return fd;
>  }