svn commit: r320803 - head/sbin/mount

[Edward Tomasz Napierala]

On 0708T1102, Ian Lepore wrote:
> On Sat, 2017-07-08 at 09:50 -0700, Rodney W. Grimes wrote:
> > [ Charset UTF-8 unsupported, converting... ]
> > > 
> > > Author: trasz
> > > Date: Sat Jul  8 11:06:27 2017
> > > New Revision: 320803
> > > URL: https://svnweb.freebsd.org/changeset/base/320803
> > > 
> > > Log:
> > >   Fix "mount -uw /" when the filesystem type doesn't match.
> > >   
> > >   This basically makes "mount -uw /" work when the filesystem
> > >   mounted on / is NFS, but the one configured in fstab(5) is UFS,
> > >   which can happen when you forget to modify fstab.
> > Please do not silence user errors because they are inconvinient,
> > this is a configuration error and the system should fail to 
> > mount the incorrectly configured root.
> > 
> > If we start changing things to silently ignore user configuration
> > errors we are going down a very slippery road.

It doesn't silence down the error.  What it does is it makes it possible
to use "mount -uw /" - previously it would fail in a rather nonsensical
way, by calling "mount_nfs -o upgrade,rw /dev/ada0 /".

> IMO, this change fixes the right problem, but maybe does so the wrong
> way.  Mount -u is by definition an update to an existing mount.  There
> should be no need to consult /etc/fstab for an existing mount since the
> info is available from the kernel.
> 
> Note that I say the foregoing with my user hat on.  I haven't looked at
> the code to see if there's some reason why my common-sensical way of
> thinking about it is actually impossible to implement for some reason.

I wouldn't expect it to consult fstab either, to be honest.  But it does,
and I suspect changing that would break someone's config.