Julian Elischer <jul...@whistle.com> wrote:
>On Thu, 25 Feb 1999, John Polstra wrote:
>
>[...]
>>
>> Here, you did the union mount on top of an existing mount point (da1).
>> I don't know for sure, but I suspect that this is the only case in
>> which union mounts are designed to work.
>
>I was led to believe (last time I read the code) that any directory should
>be ok for a union mount....
I was led to believe the same by the manual:
union Causes the namespace at the mount point to appear as the
union of the mounted filesystem root and the existing di-
rectory. Lookups will be done in the mounted filesystem
first. If those operations fail due to a non-existent
file the underlying directory is then accessed. All cre-
ates are done in the mounted filesystem.
I did a brief experiment on the 3.0-RELEASE machine as follows:
# mount
/dev/da0s1a on / (local, writes: sync 1163 async 18438)
procfs on /proc (local)
/dev/da0s1e on /usr (local, writes: sync 363 async 41653)
/dev/da1s1e on /www/da1 (local, writes: sync 12 async 38)
# ls da1/subdir
this_is_da1
# mount -o union /dev/da2s1e da1/subdir
# ls da1/subdir
this_is_da1 this_is_da2
#
So that machine is happy enough with union nounts on top of subdirectories.
On the 3.1-STABLE machine, I tried union mounting on top of a mount
point:
# mount
/dev/da0s1a on / (local, writes: sync 9824 async 55852)
/dev/da0s1e on /www (local, writes: sync 5484 async 10400)
procfs on /proc (local)
/dev/da0s1f on /srcdelta (local, writes: sync 2569 async 2659)
# ls /srcdelta
thing
# ls /www
apache obj
# umount /srcdelta
# mount -o union /dev/da0s1f /www
# ls /www
thing
#
Still no joy.
Is it sorrect that this magic is implemented in sys/kern/vfs_lookup.c?
The odd thing is that AFAICS no-one has made significant changes to
this code.
Tony.
--
f.a.n.finch d...@dotat.at f...@demon.net
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