On Nov 3, 2005, at 11:50 AM, Steven M. Bellovin wrote:
In message <20051103191902.GB547%hanele.ics.muni.cz@localhost>, Jachym Holecek writes:Cool. We could further have /dev union mounted to avoid the mmap() dance + saving a few bytes of code. I'll test it this night.Patch below (modified version of Dave's one).[Steven M. Bellovin]Last time I tried it, I couldn't union-mount a tmpfs over anything. Itwould be nice if that worked.Some naive tests seem to work for me (tmpfs union-over ffs2). Do you see the problem in fresh -current as well?Here's an example of a failure that doesn't occur with mfs:
Don't use a unionfs ... use a union mount! That's different from unionfs. unionfs is broken and buggy, and I would never trust it for a production system at this point. It needs too much work.
Do a "mount -t tmpfs -o union swap /dev" instead.
# mount -t tmpfs /dev/wd0b /mnt
# mount
/dev/wd0a on / type ffs (local)
tmpfs on /tmp type tmpfs (local)
kernfs on /kern type kernfs (local)
procfs on /proc type procfs (local)
tmpfs on /mnt type tmpfs (local)
# mount -t union /mnt /usr/src
mount_union: /mnt on /usr/src: Operation not supported
# mount -t union /usr/src /mnt
# mount
/dev/wd0a on / type ffs (local)
tmpfs on /tmp type tmpfs (local)
kernfs on /kern type kernfs (local)
procfs on /proc type procfs (local)
tmpfs on /mnt type tmpfs (local)
<above>:/usr/src on /mnt type union (local)
# umount /usr/src
umount: /usr/src: not currently mounted
# umount /mnt
# umount /mnt
# mount -t mfs /dev/wd0b /mnt
# mount
/dev/wd0a on / type ffs (local)
tmpfs on /tmp type tmpfs (local)
kernfs on /kern type kernfs (local)
procfs on /proc type procfs (local)
mfs:1661 on /mnt type mfs (synchronous, local)
# mount -t union /mnt /usr/src
# umount /usr/src
# mount -t union /usr/src /mnt
# umount /mnt
# umount /mnt
--Steven M. Bellovin, http://www.cs.columbia.edu/~smb
-- thorpej