[ ssic-linux-Bugs-2010447 ] OpenSSI fails the glibc tst-atime test

Bugs item #2010447, was opened at 2008-07-04 11:19
Message generated for change (Comment added) made by hughesj
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Category: Filesystem
Group: default
Status: Open
Resolution: None
Priority: 1
Private: No
Submitted By: John Hughes (hughesj)
Assigned to: Nobody/Anonymous (nobody)
Summary: OpenSSI fails the glibc tst-atime test

Initial Comment:
CFS doesn't keep the atime (last accessed time) field up to date.

This is a known limitation, I'm just reporting it here so it doesn't get forgotten about.

Maybe as a workaround we could pretend that cfs filesystems were mounted with the noatime option?

To reproduce:

$ cc tst-atime.c
$ ./a.out 
atime has not changed


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Comment By: John Hughes (hughesj)
Date: 2008-10-24 12:23

Message:
What's very bizarre is that this sometimes works on nodes other than the
one where the underlying filesystem is mounted, the access time seems to
get changed the first time a file is read, but not afterwards.

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Comment By: John Hughes (hughesj)
Date: 2008-10-19 18:04

Message:
Actually the:
  rootfs / rootfs
stuff is not specific to OpenSSI.

What happens in statvfs is it looks for a mountpoint with the same
filesystem type as the file it's been given (so it's looking for ext2/ext3)
but from /proc our fs shows up as cfs, so it doesn't see that it's the same
one.

Later on it retries without the type, but this time around the "rootfs /
rootfs" one matches and that doesn't have the flags.


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Comment By: John Hughes (hughesj)
Date: 2008-10-19 17:32

Message:
Simple idea, just do this at user level by remounting the fs with an
explicit noatime option:

  mount -o remount,noatime /

doesn't work because statvfs reads /proc/mounts to find the mount options
and some of the weird crud we have hanging around confuses it:

# cat /proc/mounts
rootfs / rootfs rw 0 0
/dev2/root2 / cfs rw,noatime,chard,node=1 0 0
...

Which is the real root?  Apparently statvfs thinks it's the first one.


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