From: Paolo Bonzini <pbonzini@redhat.com>
To: Markus Armbruster <armbru@redhat.com>
Cc: "Philippe Mathieu-Daudé" <philmd@redhat.com>,
qemu-devel <qemu-devel@nongnu.org>
Subject: Re: [RFC PATCH] qapi: Incorrect attempt to fix building with MC146818RTC=n
Date: Wed, 22 Jan 2020 15:30:59 +0100 [thread overview]
Message-ID: <3b991266-de2a-a9a6-ef68-1791f7bd838b@redhat.com> (raw)
In-Reply-To: <87tv4oyrnj.fsf@dusky.pond.sub.org>
On 22/01/20 06:41, Markus Armbruster wrote:
> Paolo Bonzini <pbonzini@redhat.com> writes:
>
>> Il mar 21 gen 2020, 15:22 Markus Armbruster <armbru@redhat.com> ha scritto:
>>
>>>> To see it a different way, these are the "C bindings" to QMP, just that
>>>> the implementation is an in-process call rather than RPC. If the QAPI
>>>> code generator was also able to generate Python bindings and the like,
>>>> they would have to be the same for all QEMU binaries, wouldn't they?
>>>
>>> Ommitting the kind of #if we've been discussing is relatively harmless
>>> but what about this one, in qapi-types-block-core.h:
>>>
>>> typedef enum BlockdevDriver {
>>> BLOCKDEV_DRIVER_BLKDEBUG,
>>> [...]
>>> #if defined(CONFIG_REPLICATION)
>>> BLOCKDEV_DRIVER_REPLICATION,
>>> #endif /* defined(CONFIG_REPLICATION) */
>>> [...]
>>> BLOCKDEV_DRIVER__MAX,
>>> } BlockdevDriver;
>>>
>>
>> Well, I don't think this should be conditional at all. Introspection is a
>> tool to detect unsupported features, not working features.
>
> Isn't this what it does? To detect "replication" is unsupported, check
> whether it's absent, and "supported" does not imply "works".
Indeed...
>> KVM will be
>> present in introspection data even if /dev/kvm doesn't exist on your
>> machine or you don't have permission to access it.
>
> Yes.
>
> QAPI/QMP introspection is compile-time static by design. It can't tell
> you more than "this QEMU build supports X".
... and I think it would be fine even if it told you less: "this QEMU
will not give a parse error if X appears in QMP syntax". For example,
QEMU could accept "replication" even if CONFIG_REPLICATION is not
defined and therefore using it would always fail. This would allow
limiting even more use of conditional compilation.
Paolo
next prev parent reply other threads:[~2020-01-22 14:32 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-31 18:49 [RFC PATCH] qapi: Incorrect attempt to fix building with MC146818RTC=n Philippe Mathieu-Daudé
2020-01-07 10:34 ` Paolo Bonzini
2020-01-13 14:01 ` Markus Armbruster
2020-01-18 20:47 ` Paolo Bonzini
2020-01-21 5:49 ` Markus Armbruster
2020-01-21 8:16 ` Paolo Bonzini
2020-01-21 14:22 ` Markus Armbruster
2020-01-21 14:48 ` Philippe Mathieu-Daudé
2020-01-21 20:44 ` Paolo Bonzini
2020-01-22 5:41 ` Markus Armbruster
2020-01-22 14:30 ` Paolo Bonzini [this message]
2020-01-23 8:21 ` Markus Armbruster
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