[9fans] Union mount directory behavior?

[9fans] Union mount directory behavior?

[Nathaniel W Filardo]

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I don't actually know if this is incorrect behavior, but it strikes me as
funny:

term% ramfs -m /n/ram1
term% ramfs -m /n/ram2
term% bind /n/ram1 /n/ram
term% bind -a /n/ram2 /n/ram
term% mkdir /n/ram1/test
term% mkdir /n/ram2/test
term% touch /n/ram1/test/foo
term% touch /n/ram2/test/bar
term% ls -l /n/ram
d-rwxrwxr-x M 47 nwf nwf 0 Jan 27 23:55 /n/ram/test
d-rwxrwxr-x M 45 nwf nwf 0 Jan 27 23:55 /n/ram/test
term% ls -l /n/ram/test
--rw-rw-r-- M 45 nwf nwf 0 Jan 27 23:55 /n/ram/test/foo
term% cat /n/ram/test/bar
cat: can't open /n/ram/test/bar: '/n/ram/test/bar' does not exist

Why don't I see /n/ram/test/bar?

Kernel sources are relatively recent (replica/pull done a few days ago) but
the same behavior happens in 9vx, which makes me think it's deliberate...
but the existence of /rc/bin/replica and /386/bin/replica both suggests to
me that these are supposed to be unioned together to allow replica/... to
work at a command prompt?

--nwf;

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Re: [9fans] Union mount directory behavior?

[Russ Cox]

> term% ramfs -m /n/ram1
> term% ramfs -m /n/ram2
> term% bind /n/ram1 /n/ram
> term% bind -a /n/ram2 /n/ram
> term% mkdir /n/ram1/test
> term% mkdir /n/ram2/test
> term% touch /n/ram1/test/foo
> term% touch /n/ram2/test/bar
> term% ls -l /n/ram
> d-rwxrwxr-x M 47 nwf nwf 0 Jan 27 23:55 /n/ram/test
> d-rwxrwxr-x M 45 nwf nwf 0 Jan 27 23:55 /n/ram/test
> term% ls -l /n/ram/test
> --rw-rw-r-- M 45 nwf nwf 0 Jan 27 23:55 /n/ram/test/foo
> term% cat /n/ram/test/bar
> cat: can't open /n/ram/test/bar: '/n/ram/test/bar' does not exist
>
> Why don't I see /n/ram/test/bar?

Unions are not recursive.
You put two directories named test in /n/ram.
Because of the -a on the second bind, the one
from ram1 comes first.  When you cd into test,
you get the one from ram1.  That one only contains foo.

Russ