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SubjectRe: knfsd and submounts
Miquel van Smoorenburg wrote:
> According to Dominik Kubla:
> > Hmm, let's see. says:
> >
> > Emulate Sun NFS daemon
> > If you would like for the server to allow clients to access
> > directories that are mount points on the local filesystem (this is
> > how nfsd behaves on Sun systems), say yes here. If unsure, say N.
> >
> > Ah, I see! That's the equivalent to unfsd's "--re-export" option, right?
> No, I don't think so ..
> Say you have /usr/fnord on your root filesystem. Then, /usr gets mounted
> and /usr/fnord dissapears. When you export / over NFS, /usr is not exported.
> Do you now get to see /usr/fnord on the NFS client, or not? _That_ is
> what the option CONFIG_NFSD_SUN does, at least if I'm understanding
> things correctly.

Mine works thusly. I've got the following mount points:
/dev/hda1 on / type ext2 (rw)
/dev/hda6 on /home type ext2 (rw)
/dev/hda2 on /usr type ext2 (rw)
/dev/hda5 on /var type ext2 (rw)

In /etc/exports, one of my shares is:

/ reliant(rw,no_root_squash) excelsior

Now, locally, I do an ls:
[root@ds9 /root]# ls /usr
X11R6/ doc/ i386-redhat-linux/ info/ local/ reliant/
bin/ etc/ i486-linux-libc5/ lib/ lost+found/ sbin/
dict/ games/ include/ libexec/ man/ share/

From reliant, I mount the ds9:/ export and do an ls of the
<mountpoint>/usr directory:
Connection to ds9 closed.
me2v:reliant me2v$ su -c 'mount ds9:/ /mnt/ds9'
me2v:reliant me2v$ ls /mnt/ds9/usr
me2v:reliant me2v$

Now, the kernel was configured with the following Network File System
# Network File Systems
# CONFIG_CODA_FS is not set
# CONFIG_NCP_FS is not set

Plainly, the CONFIG_NFSD_SUN does something other than what the says it does. I'm not sure what, but it *doesn't* allow
submounts to be viewed as part of the total exported filesystem; only
the physical partition is exported, and not any of the other partitions
mounted on the exported partition (I know, we export directories, by for
clarity's sake...)

> > So the only way to export say a multigigabyte FTP server without to much
> > hassle is to put the filesystem on a software RAID or LVM. (Which i had
> > so i did not experience that particular problem in the first place.)
> > That's suboptimal.
> Yup..

Yes, definitely sub-optimal. However, also, definitely something to
drool over... ;)

Matthew Vanecek
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