Messages in this thread | | | Date | Tue, 13 Jan 2004 13:46:49 -0500 | From | Mike Waychison <> | Subject | Re: [autofs] [RFC] Towards a Modern Autofs |
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raven@themaw.net wrote:
>On Mon, 12 Jan 2004, Mike Waychison wrote: > > > >>>Transparency of an autofs filesystem (as I'm calling it) is the situation >>>where, given a map >>> >>>/usr /man1 server:/usr/man1 >>> /man2 server:/usr/man2 >>> >>>where the filesystem /usr contains, say a directory lib, that needs to be >>>available while also seeing the automounted directories. >>> >>> >>> >>> >>> >>I see. This requires direct mount triggers to do properly. Trying to >>do it with some sort of passthrough to the underlying filesystem is a >>nightmare waiting to happen.. >> >> >> > >So what are we saying here? > >We install triggers at /usr/man1 and /usr/man2. >Then suppose the map had a nobrowse option. > > This is a direct map. The browse / nobrowse options do not apply to direct maps.
>Does the trigger also take care of hiding man1 and man2? > > > No. man1 and man2 appear as directories to anyone doing an lstat on them. Traversing *into* them will cause filesystems to be mounted on them. This appears to be similar to browsing of an indirect map at first, however it is a different beast. With indirect maps, we are given the right to cover up /usr to help us detects stats and traversals into its sub-directories. With direct entries, we don't have these leisure. Everything in /usr most be accessible at all times.
Your need for 'transparency' comes from the fact that you convert direct maps into indirect maps, which require the covering of /usr.
>Is there some definition of these triggers? > > > This question is up in the air.
I propose using a magic filesystem, whose root dentry has a follow_link callback defined. When somebody walks into the filesystem, the follow_link is called, which does the mount onto a different dentry, and then forwards the original caller to the new vfsmount/dentry pair.
HPA and Viro believe this is better done in the VFS layer directly by using special vfsmounts without super_blocks. The path walking code would be modified to know of these 'traps' or 'triggers' natively.
Which solution is best is left as an exercise.
-- Mike Waychison Sun Microsystems, Inc. 1 (650) 352-5299 voice 1 (416) 202-8336 voice mailto: Michael.Waychison@Sun.COM http://www.sun.com
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