Subject: O_NOATIME and files in /proc
From: Bernd Petrovitsch <bernd@firmix.at>
To: linux-kernel@vger.kernel.org, Alexey Dobriyan <adobriyan@gmail.com>,
       Andrew Morton <akpm@linux-foundation.org>
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Organization: Firmix Software GmbH
Date: Tue, 17 Nov 2009 18:06:29 +0100
Message-Id: <1258477590.16246.35.camel@tara.firmix.at>
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Hi all!

Is there a specific reason that open can not open files (at
least /proc/noatime and /proc/cpuinfo) under /proc with NO_ATIME as the
following program shows:
----  snip  ----
{12}cat noatime.c

#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>

int main(void)
{
	int fd = open("/proc/uptime", O_RDONLY|O_NOATIME);
	if (fd == -1) {
		printf("fd=%d, errno=%s\n", fd, strerror(errno));
	} else {
		printf("fd=%d\n", fd);
	}
	return 0;
}
----  snip  ----
When I compile and run it, it prints
----  snip  ----
{13}./noatime 
fd=-1, errno=Operation not permitted
----  snip  ----
Removing the "NO_ATIME" makes it work (of course).

I can also set the "noatime" mount flag on a remount and it shows up
in /proc/mounts but it makes for the above no difference.

	Bernd
-- 
Firmix Software GmbH                   http://www.firmix.at/
mobil: +43 664 4416156                 fax: +43 1 7890849-55
          Embedded Linux Development and Services


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