#166 OpenSSI fails the glibc tst-atime test

default
open
Filesystem (49)
5
2010-11-13
2008-07-04
John Hughes
No

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

Discussion

  • John Hughes

    John Hughes - 2008-07-04
     
  • John Hughes

    John Hughes - 2008-07-04
    • labels: --> Filesystem
     
  • Roger Tsang

    Roger Tsang - 2008-07-05
    • milestone: --> default
    • priority: 5 --> 1
     
  • John Hughes

    John Hughes - 2008-10-19

    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.

     
  • John Hughes

    John Hughes - 2008-10-19

    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.

     
  • John Hughes

    John Hughes - 2008-10-24

    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.

     
  • Roger Tsang

    Roger Tsang - 2010-06-20
    • priority: 1 --> 5
     
  • Roger Tsang

    Roger Tsang - 2010-11-13
    • assigned_to: nobody --> rogertsang
     
  • Roger Tsang

    Roger Tsang - 2010-11-13

    Testing a patch. So far successfully tested at server.

     
  • Nobody/Anonymous

    Tracker.. Huh, really? :)

     

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No, thanks