Re: stacked NFS mounts

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>> But we should also be fixing our code, so that umount -f *never*
>> fails (for anything except the root), no matter what else happens
>> (the -R just stops the umount program from causing issues).
> Yes.

Agreed.  But part of the problem is that - at least in 5.2 - the path
provided to unmount(2) is handed to a namei walk to find the relevant
structs vnode and mount, which of course will fail if it involves
walking through a dead NFS mount.

I'm going to look at 5.2 to see how hard it looks to have
unmount(,MNT_FORCE) do string comparisons in the mount table instead of
a namei walk.  There is the case of having two things mounted on the
same path, but that shouldn't be unsolvable.

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