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Re: [PATCH] vl, qemu-config: remove -set
From: |
Markus Armbruster |
Subject: |
Re: [PATCH] vl, qemu-config: remove -set |
Date: |
Thu, 12 Nov 2020 07:55:34 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) |
Paolo Bonzini <pbonzini@redhat.com> writes:
> On 11/11/20 16:03, Daniel P. Berrangé wrote:
>> On Wed, Nov 11, 2020 at 08:57:16AM -0500, Paolo Bonzini wrote:
>>> -set as far as I can see has basically no use. It was intended as an
>>> override
>>> mechanism for configuration files, but even configuration files themselves
>>> are hardly used. Drop it with prejudice.
>>>
>>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>>> ---
>>> docs/system/deprecated.rst | 6 ++++++
>>> include/qemu/config-file.h | 1 -
>>> qemu-options.hx | 9 ---------
>>> softmmu/vl.c | 4 ----
>>> util/qemu-config.c | 33 ---------------------------------
>>> 5 files changed, 6 insertions(+), 47 deletions(-)
>>
>> iotest 068 uses -set and qtest vhost-user-text.c also does
>> IOW, it looks like it is valid to use -set, even if you're not using
>> -readconfig.
Of course that's valid.
>> Libvirt doesn't use -set, but we've had users who make use of
>> libvirt
>> command line passthrough for QEMU with -set.
>
> Hmm, indeed:
>
> https://patchwork.kernel.org/project/qemu-devel/patch/20181218041625.24969-16-mst@redhat.com/
Such monkey-patching may not be wise, but unwise != invalid.
>> IOW, I'm not convinced real world usage is near zero as suggested.
Guessing the gamut of usage out there in the real world correctly is
always a tall order :)
> Yes, perhaps it's not. :) Though for both tests you pointed out it's
> even cleaner not to use it, there seems to be real world usage at
> least with "device".
I have common test configurations files for -readconfig. I've used -set
for quick monkey-patching once in a great while. Now, such ad hoc use
is a *weak* argument against ditching the feature. But it does
undermine the "basically no use" proposition.
> It is probably more viable to deprecate or even forbid usage of "-set"
> with anything but "device". vhost-user-test.c would still be
> affected, but it's a relatively small patch.
Deprecating only some uses buys us next to nothing, I think. If we want
to deprecate it, just deprecate it.
Immediate removal of -set / rejection of -set for some option groups
needs more justification than just "I think we can get away with it":
there has to be a tangible benefit. What would immediate removal buy us
over the orthodox "deprecate, wait for grace period to expire, remove"?