NFS access to loopback mounts

DISCUSSION Keith Owens 2 participants 2 messages Apr 11, 2002

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Keith Owens

author

2002-04-11 05:41 UTC #0 lore raw

Is accessing a loopback mount via NFS supposed to work or not? If not, how do you export iso contents without duplicating the entire iso?

Machine A.
mount -t iso9660 -o ro,loop /foo/iso /mnt/iso /etc/exports contains /mnt *(rw,no_root_squash,no_all_squash)

Machine B.
mount -t nfs A:/mnt/iso /local/iso

B says
mount: A:/mnt/iso failed, reason given by server: Permission denied
A says
rpc.mountd: authenticated mount request from ... for /mnt/iso(/mnt) rpc.mountd: getfh failed: Operation not permitted

strace rpc.mountd on A
stat64("/mnt/iso", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 nfsservctl(0x8, 0xbfffda80, 0x80553a0) = -1 EPERM (Operation not permitted)

If A does not have the loopback mounted then B can mount A:/mnt/iso over NFGS, getting an empty directrory. Not a permission problem.

A and B are running 2.4.18-XFS, nfs-utils-0.3.1-13, mount-2.11g-5. A is built with

CONFIG_NFS_FS=m
CONFIG_NFS_V3=y
# CONFIG_ROOT_NFS is not set
CONFIG_NFSD=m
CONFIG_NFSD_V3=y
CONFIG_SUNRPC=m
CONFIG_LOCKD=m
CONFIG_LOCKD_V4=y

I have a note from April 2000 where NFS access to a loopback mount used to work. Before I dig through two years of kernels to find out where it stopped working, is it valid to access loopback via NFS?

AFAIK doing NFS first then loopback on the local NFS directory has never worked.

Bill Davidsen

2002-04-11 13:25 UTC #1 lore raw

Quoted 10 lines · Keith Owens

Is accessing a loopback mount via NFS supposed to work or not? If not, how do you export iso contents without duplicating the entire iso?
Machine A.
mount -t iso9660 -o ro,loop /foo/iso /mnt/iso /etc/exports contains /mnt *(rw,no_root_squash,no_all_squash)
Machine B.
mount -t nfs A:/mnt/iso /local/iso

Quoted 6 lines

I have a note from April 2000 where NFS access to a loopback mount used to work. Before I dig through two years of kernels to find out where it stopped working, is it valid to access loopback via NFS?
AFAIK doing NFS first then loopback on the local NFS directory has never worked.

I usually export a CD by mounting and exporting that, actually. If you
have the space for the ISO I would think that just copying it from CD to a hierarchy would take no more space (although if you want to have the ISO image handy for burning that would take more space).

Can you export the directory with the ISO image and do a loopback mount
on the client end? haven't tried that, and I'm working on a laptop at the end of a slow modem this morning, so I'm not able to try it here.

Oops, I'm wrong, I could ssh into a machine with an NFS directory
containing ISO images, and I did nicely mount one and look at the contents.

So to answer your questions, I have no idea why it doesn't work, but you
can get around it if the NFS client is a Linux machine.

While we're mentioning loopback problems, mounting a CD with loopack and
offset:
mount -o ro,loop,offset=7480 /dev/cdrom /mnt
used to work and doesn't. I get these CDs all the time with a chunk of binary data of variable length and an ISO image. Used to work, and I can mount them on 2.0 and 2.2 systems still. I posted that one before and got no feedback other than one private E-mail saying that the format was dumb and I should change it. Since it works for the client and is written by hardware, LOL.

Signature · 3 lines

bill davidsen <[email protected]>
  CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.