mergemaster improvement (auto-update for not modified files)

[M. Warner Losh]

In message: <20050503222512.GA53874 at crow.addict.de>
            Juergen Unger <j.unger at addict.de> writes:
: On Tue, May 03, 2005 at 11:15:51AM -0700, Julian Elischer wrote:
: > c0ldbyte wrote:
: [...]
: > >But with all due respect, This just seems like another case of a
: > >"Bike Shed" incident.
: > not at all.
: > I've wanted this for a long time..
: > files that I have not touched are at default state and I wnat them to move 
: > to teh new default state. Files I have touched, I want to look at by hand.
: 
: so do I.  And to go a step further: why do we at all have to run
: this things in single-user mode ?
: Not that I am not aware of the technical reasons for it

The technical reasons are very simple.  If a new system call is
created, and programs use that new system call, then if you do an
installworld before you boot the kernel, that can result in binaries
not working.  This has happened with important ones like /bin/sh in
the past.  In addition, if you aren't running single user, many
different races exist in the installation process that can result in
bad behavior.  There are also potential problems with symbols in
there's a large jump between the revisions being updated.

Usually you can get away with it, but if you want to be safe, you must
do the install in single user.  Usually, however, has lead in the past
to problems, which is why the project recommendations are
conservative.

Warner