Ben Hutchings:
> Well, I don't understand how this is going wrong.  All the logic in
> fs/nfs/super.c (nfs_show_mount_options(), nfs_remount(),
> nfs_parse_security_flavors(), nfs_compare_remount_data()) appears to do
> the right thing with the sec option (stored in various structures as
> auth_flavors[0] or au_flavor).
>
> Perhaps you could add some debug logging to work out how the option is
> getting mangled on remount?

Unfortunately, I don't remember the detail of wheezy 3.2 kernel because
I am reading various versions of mainline kernel. I am going to slightly
mad and confused.

I only remember that
- At the first mount-time, NFS sets RPC_AUTH_UNIX (as default) without
  NFS_MOUNT_SECFLAVOUR.
- nfs_show_mount_options() prints "sec=sys" since RPC_AUTH_UNIX is set,
  but still NFS_MOUNT_SECFLAVOUR is not set.
- "mount -o remount" retrives "sec=sys" from /proc/mounts and passes it
  to mount(2).
- nfs_remount() --> nfs_parse_mount_options() --> nfs_compare_remount_data()
  compares the flags and found that
  - "sec=sys" string is given.
  - but NFS_MOUNT_SECFLAVOUR flag is not set internally.
  and returns EINVAL.

I guess one possible solution is stop printing "sec=" in
nfs_show_mount_options() when NFS_MOUNT_SECFLAVOUR is not set.
Another solution can be to force setting NFS_MOUNT_SECFLAVOUR when
setting RPC_AUTH_UNIX as default. But in this case, we may need to care
about /etc/mtab.
In other words,
- it may be hard to keep /etc/mtab and /proc/mounts equivalent.
- some developers think
  + /etc/mtab and /proc/mounts are totally different things
  + it is unnecessary to make them equivalent.
- finally symlinking /etc/mtab can cause a problem (like this case)
  since mount(8) and umount(8) highly depends upon /etc/mtab (or
  /proc/mounts).

By the way, after forcing /etc/mtab as a regular file on my wheezy
system, I found another problem of mount(8). I will report it to
bugtrack later.


J. R. Okajima


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