[PATCH] virhostcpu: Fix build with clang and newest kernel headers

[Peter Krempa]

On Tue, Aug 23, 2022 at 16:38:46 +0200, Michal Prívozník wrote:
> On 8/23/22 16:15, Peter Krempa wrote:
> > The most recent environment e.g. present in our Fedora Rawhide builds
> > fail to build the tree with clang with the following error:
> > 
> > ../src/util/virhostcpu.c:1291:25: error: field 'header' with variable sized type 'struct kvm_msrs' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end]
> >         struct kvm_msrs header;
> >                         ^
> > 
> > The problem seems to be that clang doesn't like the new way the
> > 'entries' field in struct kvm_msrs is declared.
> > 
> > To work around the issue we can simply allocate the variable dynamically
> > and use the 'entries' member as it was intended to to access the
> > members.
> > 
> > Signed-off-by: Peter Krempa <pkrempa at redhat.com>
> > ---
> >  src/util/virhostcpu.c | 15 ++++++---------
> >  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> Yeah, since this code is heavily inspired by QEMU I wanted to wait a bit
> to see how QEMU deals with this because allocating those few bytes
> looked needless to me. But I guess there's no better solution. Anyway,

This is a usual way how we deal with such structs e.g. in
virNetDevGetEthtoolGFeatures. Additionally now it uses the intended
accessor declared in 'struct kvm_msrs'.

Also we have A LOT places where we allocate short temp strings just to
format something. I'd not worry about overhead too much.