fs/9p: regression in 6.8-rc1

[Eric Van Hensbergen <ericvh@kernel.org>]

I caught a problem in the new netfs code when running in 9p when running
with nocache mode.  A regression sweep is turning up a:
 [ 1084.438387] netfs: Zero-sized write [R=1b6da]
when running my ldconfig test (included at the end of this)
it reports:
/sbin/ldconfig.real: Writing of cache extension data failed: Input/output error

I will try to dig into this later today if I have time, but not sure I'll get
to it so I wanted to make other folks aware.  I'm not sure how much other
elements of my test harness are contributing to reproducing the problem.

	-eric

--snip--
# setup chroot

mount -o bind /dev /mnt/9/dev
mount -o bind /sys /mnt/9/sys

# test mmap via ldconfig doesn't produce lots of errors

chroot /mnt/9 ldconfig -C /tmp/testldconfig.cache > $LOG.log 2>&1

if [ -s $LOG.log ]; then
    echo "FAIL"
else
    echo "SUCCESS"
fi