Test to trace kernel bug in fsconfig(2) with nfs

[Richard Haines <richard_c_haines@btinternet.com>]

The test program 'fsmount.c' sent in [1], can be used along with the
test script below to show a kernel bug when calling fsconfig(2) with
any valid option for an nfs mounted filesystem.

This problem is not related to the btrfs bug I reported in [1], however
I suspect that once vanilla NFS options can be set, it may uncover the
same issue as in [1].

[1] 
https://lore.kernel.org/selinux/c02674c970fa292610402aa866c4068772d9ad4e.camel@btinternet.com/T/#u

Copy the statements below into nfs-test.sh and run.

MOUNT=/home # must be a top-level mount
TESTDIR=$MOUNT/MOUNT-FS-MULTI/selinux-testsuite
systemctl start nfs-server
exportfs -orw,no_root_squash,security_label localhost:$MOUNT
mkdir -p /mnt/selinux-testsuite
# mount works:
#mount -t nfs -o
"vers=4.2,rootcontext=system_u:object_r:unconfined_t:s0"
localhost:$TESTDIR /mnt/selinux-testsuite
# Both of these give: Failed fsconfig(2): Invalid argument (nfsvers=4.2
or vers=4.2 fail)
./fsmount nfs localhost.localdomain:$TESTDIR /mnt/selinux-testsuite
"nfsvers=4.2"
#./fsmount nfs localhost.localdomain:$TESTDIR /mnt/selinux-testsuite
"nfsvers=4.2,rootcontext=system_u:object_r:unconfined_t:s0"
umount /mnt/selinux-testsuite
exportfs -u localhost:$MOUNT
systemctl stop nfs-server