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Re: [Qemu-devel] [PULL 14/15] qapi: Don't box branches of flat unions
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PULL 14/15] qapi: Don't box branches of flat unions |
Date: |
Tue, 23 Feb 2016 08:18:55 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 |
On 02/23/2016 07:50 AM, Daniel P. Berrange wrote:
> On Fri, Feb 19, 2016 at 01:18:05PM +0100, Markus Armbruster wrote:
>> From: Eric Blake <address@hidden>
>>
>> There's no reason to do two malloc's for a flat union; let's just
>> inline the branch struct directly into the C union branch of the
>> flat union.
>>
>
> My code needs todo something a little different though - it needs
> to directly visit one of the union branches. Previously, I could
> allocate a QCryptoBlockOptions and then visit a specific union
> branch like this:
>
> QCryptoBlockOptions *opts = NULL;
>
> opts = g_new0(QCryptoBlockOptions, 1);
> opts.format = Q_CRYPTO_BLOCK_FORMAT_LUKS
>
> visit_type_QCryptoBlockOptionsLUKS(v, "luks", &opts.u.luks, errp)
which allocated a pointer and visited the fields. We no longer need the
pointer, but still need the fields visited.
>
>
> I need todo this, because my visitor instance does not have any
> 'format' field to visit - we know the format upfront from the
> block layer driver choice. So we need to directly visit the
> appropriate inline union branch. This no longer works, because
> the opts.u.luks field is now inlined instead of being boxed :-(
You're using OptsVisitor, right? Is it possible to hack the QemuOpts
that you feed to opts_visitor_new() to include a 'format' field?
>
> I could visit_type_QCryptoBlockOptionsLUKS_fields(v, opts.u.luks, errp)
> but the '_fields' methods are all declared static in qapi-visit.c
> preventing their use.
>
> IMHO, now that QAPI inlines the flat unions, we should be making
> the _fields() methods public.
But my suggestion would just be a hack. Yours makes more sense in the
long run, so I'll go ahead and propose that patch.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- [Qemu-devel] [PULL 06/15] qapi-visit: Simplify how we visit common union members, (continued)
- [Qemu-devel] [PULL 06/15] qapi-visit: Simplify how we visit common union members, Markus Armbruster, 2016/02/19
- [Qemu-devel] [PULL 10/15] qapi: Adjust layout of FooList types, Markus Armbruster, 2016/02/19
- [Qemu-devel] [PULL 13/15] qapi: Don't box struct branch of alternate, Markus Armbruster, 2016/02/19
- [Qemu-devel] [PULL 03/15] qapi: Forbid empty unions and useless alternates, Markus Armbruster, 2016/02/19
- [Qemu-devel] [PULL 11/15] qapi: Emit structs used as variants in topological order, Markus Armbruster, 2016/02/19
- [Qemu-devel] [PULL 07/15] qapi: Visit variants in visit_type_FOO_fields(), Markus Armbruster, 2016/02/19
- [Qemu-devel] [PULL 05/15] qapi: Add tests of complex objects within alternate, Markus Armbruster, 2016/02/19
- [Qemu-devel] [PULL 15/15] qapi: Change visit_start_implicit_struct to visit_start_alternate, Markus Armbruster, 2016/02/19
- [Qemu-devel] [PULL 14/15] qapi: Don't box branches of flat unions, Markus Armbruster, 2016/02/19
- Re: [Qemu-devel] [PULL 00/15] QAPI patches for 2016-02-19, Peter Maydell, 2016/02/19