From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Russ Cox" <rsc@plan9.bell-labs.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] union directories
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Date: Wed, 21 Mar 2001 21:02:58 -0500
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Actually that's the way it's supposed to work.

    Say you have two directories free_space and non_writable.
    If you write:

    bind -bc free_space non_writable 

    You add space to non_writable. Everything works fine. free_space is before
    non_writable in non_writable. If you create a file in non_writable you
    are actually creating int in free_space.

The union looks like

 * free_space
   non_writable

where the * means the directory was bound with -c.
Creates go to the topmost starred directory.

    bind -ac non_writable2 free_space2

    non_writable2 is after free_space2 in free_space2. You should be able to
    write in free_space. *you can't*. Even stranger:

Now you have

   free_space2
 * non_writable2

Creates go to non_writable2, but the directory
isn't writable.

    bind -ac fspace1 fspace2

    Any file in fspace2 supersedes any file in fspace1 with the same name,
    but if you create a file in fspace2 it is actually created *in fspace1*!!!???.
    fspace1 is *after* fspace2 for already existing files,
    but it is *before* when you create new ones.

Now you have

   fspace2
 * fspace1

Creates go to fspace1 but fspace2 wins for lookups.

It's just the way it's defined.  Note that if you did

bind -c fspace2 fspace2
bind -ac fspace1 fspace2

you'd have

 * fspace2
 * fspace1

so creates would go to fspace2 (the fact that fspace1
is starred is ignored), and fspace2 would win for lookups.

Russ