Re: [RFC] union-mount stuff

From: almesber@lrc.di.epfl.ch
Date: Thu Jun 08 2000 - 04:22:07 EST


Alexander Viro wrote:
> Not. union-mount != unionfs, it does not descend into subdirectories.
> There is no way in hell to do that and permit sharing the union-mount
> components between several mountpoints. unionfs is very different animal
> and there the main point is that you are getting real, honest
> copy-on-write,

Hmm, now I'm throughly confused :-( What is the "union" in here then ?
Is it that a lookup for a top-level component searches all file system
in that list, or does it simply mean that all the file systems are
internally linked to the same place, but only one of them is truly
visible ?

E.g., given

# mount /dev/a /mnt
# mkdir -p /mnt/foo/blah /mnt/bar
# umount /dev/a
# mount /dev/b /mnt
# mkdir -p /mnt/foo/zulu /mnt/baz
# mount -o union /dev/a /mnt

# cd /mnt/foo/blah works ?
# cd /mnt/foo/zulu works too ? (no, I guess)
# cd /mnt/baz works ?
# cd /mnt/bar works too ?
# cd /mnt; touch file works ? on which device is the file created ?
# cd /mnt/foo; touch file works ?
# cd /mnt/foo/blah; touch file works ?
# cd /mnt/foo/zulu; touch file works too ? (no, I guess)

Maybe you should define what you mean by "union" ... seems that
everybody has a slightly different idea of what it should mean.

- Werner

-- 
  _________________________________________________________________________
 / Werner Almesberger, ICA, EPFL, CH       werner.almesberger@ica.epfl.ch /
/_IN_N_032__Tel_+41_21_693_6621__Fax_+41_21_693_6610_____________________/

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