unionfs below: only read-only?

[Daichi GOTO]

Andriy Gapon wrote:
> $ uname -srm
> FreeBSD 7.1-PRERELEASE amd64
> 
> $ mount -t unionfs -o below -o rw /usr/ports/distfiles
> /export/j386/usr/ports/distfiles
> mount_unionfs: /export/j386/usr/ports/distfiles: : Operation not supported
> Exit 71
> 
> $ mount -t unionfs -o below -o ro /usr/ports/distfiles
> /export/j386/usr/ports/distfiles
> Exit 0

I need more information to think. Please get up off result of
df(1) and mount(8).

And... check the permission of /export/j386/usr/ports/distfiles.
I'm doubting that permission of /export/j386/usr/ports/distfiles is
read only.

> My intention was to mount /usr/ports/distfiles into a jail but in such
> way that jail can not modify any "global" files but can add some files
> of its own.
> This is similar to the last example in mount_unionfs(8):
> mount -t unionfs -o noatime -o below /sys $HOME/sys
> 
> But it seems that with -o below I can mount a filesystem only in RO mode
> which is totally useless because I can not write anything to "uniondir"
> i.e. /export/j386/usr/ports/distfiles:
> $ cp ~/tar/diablo-caffe-freebsd6-i386-1.5.0_07-b01.tar.bz2
> /export/j386/usr/ports/distfiles/
> cp:
> /export/j386/usr/ports/distfiles/diablo-caffe-freebsd6-i386-1.5.0_07-b01.tar.bz2:
> Read-only file system
> Exit 1
> 
> So effectively this is a nullfs ro mount.
> 
> Is there a buglet or am I missing something?
> 


-- 
   Daichi GOTO, http://people.freebsd.org/~daichi