>Number:         28472
>Category:       kern
>Synopsis:       NFS client gets atime wrong
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Nov 30 00:24:00 +0000 2004
>Originator:     Brian Marcotte
>Release:        NetBSD 2.0_RC4
>Organization:
	panix.com
>Environment:
	kernel and userland match
System: NetBSD panix5.panix.com 2.0_RC4 NetBSD 2.0_RC4 (PANIX-USER) #0: Sat Nov 6 19:39:39 EST 2004 root@trinity.nyc.access.net:/devel/netbsd/release-2.0-20041022/src/sys/arch/i386/compile/PANIX-USER i386
Architecture: i386
Machine: i386
>Description:
	The NFS client sometimes updates the atime when it shouldn't or
	doesn't update it when it should. Or perhaps the NFS client does
	not do the right things to make the server update, or not update
	the atime.

	This can cause programs which check for new mail to never report
	the presence of new mail. It appears that on mail delivery the
	atime is set to the mtime (the time of delivery) which is
	incorrect behavior.

	Note that our NFS server is a NetAPP and hasn't changed in years.
	We noticed this problem in 2.0. I don't know if its a problem in
	the 1.6 series. It worked fine in 1.5.
>How-To-Repeat:

This short script will show the problem. Run it in an NFS mounted
directory.

In the first example, it is interesting that the problem occurs
only when the numbers of writes is 2 or greater ("count=2").

I have verified that this works fine on FFS.

	#!/bin/sh

	rm -f file
	echo "Example where atime is updated when it shouldn't be."
	echo "This is similar to when mail is delivered to a mailbox."
	echo
	for x in 1 2 3 ; do
	        dd if=/dev/zero bs=1 count=2 2> /dev/null >> file
	        echo -n "mtime: " ; ls -lT file
	        echo -n "atime: " ; ls -luT file
	        echo
	        sleep 3
	done

	echo

	rm -f file
	echo "Example where atime is NOT updated when it should be:"
	echo
	touch file
	for x in 1 2 3 ; do
	        cat file > /dev/null
	        echo -n "mtime: " ; ls -lT file
	        echo -n "atime: " ; ls -luT file
	        echo
	        sleep 3
	done

Here is the output on my system:

	Example where atime is updated when it shouldn't be.
	This is similar to when mail is delivered to a mailbox.

	mtime: -rw-r--r--  1 marcotte  staff  2 Nov 29 19:14:38 2004 file
	atime: -rw-r--r--  1 marcotte  staff  2 Nov 29 19:14:38 2004 file

	mtime: -rw-r--r--  1 marcotte  staff  4 Nov 29 19:14:41 2004 file
	atime: -rw-r--r--  1 marcotte  staff  4 Nov 29 19:14:41 2004 file

	mtime: -rw-r--r--  1 marcotte  staff  6 Nov 29 19:14:44 2004 file
	atime: -rw-r--r--  1 marcotte  staff  6 Nov 29 19:14:44 2004 file


	Example where atime is NOT updated when it should be:

	mtime: -rw-r--r--  1 marcotte  staff  0 Nov 29 19:14:47 2004 file
	atime: -rw-r--r--  1 marcotte  staff  0 Nov 29 19:14:47 2004 file

	mtime: -rw-r--r--  1 marcotte  staff  0 Nov 29 19:14:47 2004 file
	atime: -rw-r--r--  1 marcotte  staff  0 Nov 29 19:14:47 2004 file

	mtime: -rw-r--r--  1 marcotte  staff  0 Nov 29 19:14:47 2004 file
	atime: -rw-r--r--  1 marcotte  staff  0 Nov 29 19:14:47 2004 file

>Fix:
	unknown