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Subject[Announce][CFT] loopback mounts and stuff
	Folks, there is a cleanup of mount-related stuff underway. Right
now the patch seems to be usable for testing.
It doesn't include pieces in nfsd and auotfs*, so these simply
wont compile, but it should <knocking the wood> work with everything else.

It allows
a) to mount the same filesystem several times. Yup, ext2 included. No
cache coherency problems - all instances share the dentry tree.
b) to work with shmfs without mounting it.
c) to do explicit loopback mount. As in
# mount -t bind /usr/X11R6 /mnt
# ls /mnt
bin doc include lib man share
# cd /mnt
# ls ..
bin dev home lost+found mnt proc sbin usr
boot etc lib misc opt root tmp var
(IOW, unlike the usage of symlinks it gives correct behaviour on ..)
d) to mark filesystem type as 'single'. One superblock will be created
when you initialize the driver, all later mounts of that type will be
aliases to that one. IOW, we can start storing procfs immediately in
dcache - just a normal tree. Moreover, kernel can access that tree even
if it's not mounted by user. That's how the shmfs stuff is done. Oh, and
all instances will share the device number, so you can create a thousand
chroot jails, mount devpts on each and spend 1 (one) anonymous device.
Ditto for procfs, etc.

Patch (against 2.3.99-pre3) lives on
ftp://ftp.math.psu.edu/pub/viro/mount-patch-4.

Folks, give it a try. There may be bugs. I think that it's cleaner than
the old code, but don't let it play with critical data. Bug reports are
more than welcome, indeed. Another thing that is _very_ welcome is a
discussion of the export rules in situation when filesystems on server may
be mounted several times (as well as the current implementation - I'ld
really like to hear comments on it, in particular on the exp_parent().
It's either buggy and doesn't what it is supposed to do or contains
seriously superfluous code). General comments on the patch are also
welcome, indeed.
Cheers,
Al


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