bug#53037: df/total-verify fail with cephfs

[Dylan Simon]

>From Paul Eggert <eggert@cs.ucla.edu>, Wed, Jan 05, 2022 at 01:05:03PM -0800:
> On 1/5/22 11:27, Dylan Simon wrote:
> > Only adding rows with all known values
> > might make sense but would still break the test (wrong total total instead):
> > 
> >    if (known_value (iv->total) && known_value (iv->available)) {
> >      grand_fsu.fsu_files += iv->total;
> >      grand_fsu.fsu_ffree += iv->available;
> >    }
> 
> Sorry, I'm not quite following. If you make the above change, what will the
> output look like instead? And how will that break the test?

Then it will look like this (I'm inferring, haven't actually tried it):

Filesystem        Inodes     IUsed    IFree IUse% Mounted on
/dev/sda1       20971520    529832 20441688    3% /
ceph           901006598         -        -     - /mnt/ceph
total           20971520    529832 20441688    3% -

That is, the ceph line will just be excluded completely from the total.  Now
the used and free lines add up correctly, but total Inodes does not.