Re: [Qemu-devel] [PATCH] pc: reduce duplication, fix PIIX descriptions

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Aug 27, 2013 at 01:09:23PM -0300, Eduardo Habkost wrote:
> On Tue, Aug 27, 2013 at 09:51:22AM +0200, Markus Armbruster wrote:
> > "Michael S. Tsirkin" <mst@redhat.com> writes:
> > 
> > > We have a lot of code duplication between machine types,
> > > this increases with each new machine type
> > > and each new field.
> > >
> > > This has already introduced a minor bug: description
> > > for pc-1.3 says "Standard PC" while description for
> > > pc-1.4 is "Standard PC (i440FX + PIIX, 1996)"
> > > which makes you think 1.3 is somehow more standard,
> > > or newer, while in fact it's a revision of the same PC.
> > 
> > I wouldn't call it a bug.  We're in the habit of never changing old
> > machine types, so when we created pc-i440fx-1.4 and pc-q35-1.4 with a
> > .desc that clearly explains the difference, we didn't change the older
> > versions the PC machine types as well.
> > 
> > That may have been overly cautious.  As long as .desc is not exposed to
> > the guest, it's not ABI, thus can be changed.
> 
> I just confirmed that on qemu-system-x86_64 the only place where .desc
> is used is on the machine_parse() help/error code at vl.c. I don't know
> about other architectures.

Generally, one would hope we won't expose random
internal stuff to guests :).

> I suggest we explicitly document the field as a human-readable
> machine-type description that should be never exposed to the guest (just
> in case somebody decides to use .desc on some guest-visible table one
> day).

Where would you document this?

> -- 
> Eduardo