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

[Markus Armbruster <armbru@redhat.com>]

Eduardo Habkost <ehabkost@redhat.com> writes:

> 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.
>
> 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).

My "[PATCH v2 7/7] smbios: Set system manufacturer, product & version by
default"[*] puts .desc in SMBIOS type 1 entry product name.  Makes more
sense than our current "Bochs".

I'm fine with reserving .desc for QEMU help, I'll simply create another
member that may be exposed to the guest then.


[*] On list since mid July, Reviewed-by: Eric, Ignored-by: all
maintainers.