Messages in this thread | | | Date | Fri, 31 Aug 2007 10:01:50 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: recent nfs change causes autofs regression |
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On Fri, 31 Aug 2007, Trond Myklebust wrote: > > The best I can do given the constraints appears to be to have the kernel > first look for a superblock that matches both the fsid and the > user-specified mount options, and then spawn off a new superblock if > that search fails.
I think this is probably acceptable to get roughly the old behaviour, but I still think it's a bit stupid.
What happens at "mount -o remount,..." time?
The fact is, the whole "match the fsid and user mount options, and re-use the mount" sounds like it's trying to solve a problem that doesn't need solving. If the user really wants to duplicate the mount, he really should be using a a bind-mount instead.
In other words, let's assume that the user has /some/nfs/mount mounted over NFS, and wants to re-mount it (or even just a subset of it) somewhere else, the sane thing to do is not to mount it again, but to just do
mount --bind /some/nfs/mount/subdir /new/mount/place
instead. That *guarantees* that the low-level filesystem uses the same flags, and it also means that things like re-mounting have sane and well-defined semantics, and will fail or succeed predictably.
In contrast, if a user wants to create a new NFS mount, it really should be independent of the old one, because that's (a) what other systems do, and (b) also makes the semantics of re-mounting it with other flags be clear and unambiguous (ie the remount has nothing what-so-ever to do with the independent NFS mount).
See?
This is why I think "nosharecache" should just be the default, because that's the behaviour that simply does not have any subtle issues. The *special* case should be the "sharecache" case, and 99% of the time that one should likely be done with a "--bind" mount.
(I don't really see the point of _ever_ doing anything but a bind mount, but maybe there are reasons to try to share at a NFS layer that I don't really see)
> The attached patch does just that.
Hua, does this fix things for you? If it gets rid of the regression, I can certainly live with it, but as per above, I don't really think this makes much sense in the "bigger picture" kind of thing.
> Finally, for the record: I still feel very uncomfortable about not being > able to report the state of the client setup back to the sysadmin. > AFAIK, the only way to do so is to stat the mountpoints, and compare the > device ids.
Well, not only don't I see that as being horribly wrong, I actually think that the sysadmin should know what his mount setup is, even without having to ask. But since he *can* ask, using easy and standard interfaces, I don't really see what the problem really is.
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