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List:       amd-dev
Subject:    Re: amd mount point confusion
From:       Erez Zadok <ezk () cs ! sunysb ! edu>
Date:       2004-07-21 0:30:05
Message-ID: 200407210030.i6L0U55g005508 () agora ! fsl ! cs ! sunysb ! edu
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In message <40FCC559.4080501@sidewinderap.com>, Andrew Bergman writes:
> Sorry, I meant to say browsable dirs IS enabled.

Then you get a mount storm if you stat each entry.   You have to be careful
with "ls" b/c only plain 'ol

$ /bin/ls

may not stat each entry.  (When in doubt, strace it.)

But if you do any of these

$ ls -l
$ ls -F
$ ls --color (default on many GNU-based systems)

then you stat each entry and you get a mount storm.

> I turned this off and now I have the other extreme, nothing shows up in 
> /home unless the key has been accessed to mount the nfs share.  Only 
> active NFS mounts show up.

Correct, that's been the old behavior of Amd before browsable dirs was
added.

> Ideally what I want is to have the list of keys in /home, without 
> mounting each and every system on the network to do so.
> 
> If you say for example cd /home/<mountpoint> only then should it mount 
> it.  But with browsable dirs on it seriously took about a minute before 
> the ls showed the contents, and everything was mounted.

Sorry, the normal Unix file system model, and NFS in particular, are simply
incapable of doing so.  There's no way to distinguish b/t a stat for the
purpose of "chdir" or a "lookup below this name" vs. a stat for the purpose
of looking up the entry but not automounting it.

To to what you want, you need two things:

1. A special in-kernel file system in support of the such a feature.  This
   is called Autofs.

2. Changes to your OS (or at least your VFS) so as to create special file
   system methods for lookup vs. stat vs. chdir; then your Autofs-aware Amd
   can do browsable_dirs and avoid most mount storms.

AFAIK, only Solaris's Autofs v3 supports the above feature currently, and we
try and take advantage of it in am-utils-6.1.

> Thanks
> 
> Andy

Erez.
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