Re: [Qemu-devel] [PATCH v2] update names in option tables to match with actual command-line spelling

[Markus Armbruster <armbru@redhat.com>]

[cc: Eric yet again :)]

Paolo Bonzini <pbonzini@redhat.com> writes:

> Il 17/03/2014 09:23, Markus Armbruster ha scritto:
>> > This patch makes all names in option table to match with actual
>> > command-line spelling, it will be helpful when we search in option
>> > tables.
>>
>> As discussed in [*], the QemuOptsList member name values are ABI:
>> changing them can break existing -readconfig configuration files.  If we
>> decide breaking ABI is okay here (big if!), we need to document it
>> prominently in the commit message.
>
> I think in some (rare) cases breaking the rule is okay.  For example,
> the pending conversion of "-m" to QemuOpts uses "memory".

Breaking naming consistency rules is one thing, breaking ABI an entirely
different one.

While I'm not overly scared of the ABI change bugaboo, I do insist on
considering the implications, and on proper documentation.

> However, I don't think adding "-opts" is a good thing to do.  Which
> one is most readable?
>
>    [m]
>       size = 128M
>       max = 512M
>
>    [memory]
>       size = 128M
>       max = 512M
>
>    [memory-opts]
>       size = 128M
>       max = 512M

That's a no-brainer :)

I'm all for naming configuration file sections sensibly.  While I value
consistency between section names and command line options, I agree with
you that having sensible section names trumps consistency with the
command line.

In this case, consistency with command line could easily be preserved by
making -m sugar for --memory.

I doubt changing existing section names to make them prettier or more
consistent with the command is worth the ABI breakage.  Any inconsistent
or ugly names that haven't been released yet should be fixed right away,
of course.

This patch changes:

    from        to          introduced in
    acpi        acpitable   0c764a9 v1.5.0
    boot-opts   boot        3d3b830 v1.0
    smp-opts    smp         12b7f57 v1.6.0

All three have calcified into ABI already.

> I'm for including this patch in 2.0.

Not without explaining the ABI breakage in the commit message.  We
should also make sure to cover it in the release notes[*].

Moreover, if exceptions from the rule "QemuOptsList name must match the
name of the (non-sugared) command line option using it" are or will be
permissible, then Amos's comment on QemuOptsList member name needs to be
clarified.


[*] Release note material is being collected at
http://wiki.qemu.org/ChangeLog/2.0