getcwd lies on/under nfs4-mounted zfs dataset

[Rick Macklem]

pluknet at gmail.com wrote:
> Hi.
> 
> We stuck with the problem getting wrong current directory path
> when sitting on/under zfs dataset filesystem mounted over NFSv4.
> Both nfs server and client are 10.0-CURRENT from December or so.
> 
> The component path "user3" unexpectedly appears to be "." (dot).
> nfs-client:/home/user3 # pwd
> /home/.
> nfs-client:/home/user3/var/run # pwd
> /home/./var/run
> 
Ok, I've figured out what is going on. The algorithm in libc
works, but vn_fullpath1() doesn't. The latter assumes that
"mount points" are marked with VV_ROOT etc. For the
"pseudo mount points" (which are mount points within the
directory tree on the NFSv4 server), this isn't the case.

If you:
sysctl debug.disablecwd=1
sysctl debug.disablefullpath=1

it works. (At least for the UFS case I tested.)

I can't see how this can be made to work correctly
for vn_fullpath1() unless it was re-written to use the
same algorithm that lib/libc/gen/getcwd.c implements.

I was pretty sure this used to work. Maybe the syscalls
used to be disabled by default or weren't used by the
libc functions?

Anyhow, sorry about the cofusing posts while I figured
out what was going on, rick
ps: Don't use the patch I posted. It isn't needed and
    will break stuff.

> nfs-client:~ # procstat -f 3225
> PID COMM FD T V FLAGS REF OFFSET PRO NAME
> 3225 a.out text v r r-------- - - - /home/./var/a.out
> 3225 a.out ctty v c rw------- - - - /dev/pts/2
> 3225 a.out cwd v d r-------- - - - /home/./var
> 3225 a.out root v d r-------- - - - /
> 
> The used setup follows.
> 
> 1. NFS Server with local ZFS:
> # cat /etc/exports
> V4: / -sec=sys
> 
> # zfs list
> pool1 10.4M 122G 580K /pool1
> pool1/user3 on /pool1/user3 (zfs, NFS exported, local, nfsv4acls)
> 
> Exports list on localhost:
> /pool1/user3 109.70.28.0
> /pool1 109.70.28.0
> 
> # zfs get sharenfs pool1/user3
> NAME PROPERTY VALUE SOURCE
> pool1/user3 sharenfs -alldirs -maproot=root -network=109.70.28.0/24
> local
> 
> 2. pool1 is mounted on NFSv4 client:
> nfs-server:/pool1 on /home (nfs, noatime, nfsv4acls)
> 
> So that on NFS client the "pool1/user3" dataset comes at /home/user3.
> / - ufs
> /home - zpool-over-nfsv4
> /home/user3 - zfs dataset "pool1/user3"
> 
> At the same time it works as expected when we're not on zfs dataset,
> but directly on its parent zfs pool (also over NFSv4), e.g.
> nfs-client:/home/non_dataset_dir # pwd
> /home/non_dataset_dir
> 
> The ls command works as expected:
> nfs-client:/# ls -dl /home/user3/var/
> drwxrwxrwt+ 6 root wheel 6 Jan 10 16:19 /home/user3/var/
> 
> --
> wbr,
> pluknet
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