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DragonFly kernel List (threaded) for 2006-10
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Re: HEADS UP - possible destabilization over the next few days

From: "Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx>
Date: Fri, 27 Oct 2006 09:19:58 +0200

Matthew Dillon wrote:
    * NULLFS mounts will not create a multiplication of namecache entries.
      All NULLFS mounts will share the same namecache topology as their
      underlying filesystems.  A system with a large number of NULLFS mounts
      will use far less kernel memory now.

    * Namecache coherency between a NULLFS mount and its underlying filesystem
      will be maintained.  Since they share the same namecache topology
      there will not be visibility issues or races when a file is created,
      removed, or renamed.

Wouldn't this mean that if I mounted a FS in the NULLFS that this mountpoint will also appear in the original tree, or is that managed by nchandles as well?

It is also my hope that by associating the mount pointer directly with
the handles that access the name cache (e.g. current dir, root dir,
jail dir, open descriptors, etc), it will become possible to perform
mount-specific special actions during lookups that will allow us to
build a solid union fs or shadowing fs implementation. I won't be working on those any time soon, but the new infrastructure should make
the concepts easier to consider.

Absolutely cool. When the mount point scanning code is fast enough, I can finally see our VFS enabled package management come true: just mount all packages you want to see together into one directory.


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