On Fri, 2012-10-05 at 18:05 +0000, Blue Swirl wrote:
> On Fri, Oct 5, 2012 at 5:33 PM, Alex Williamson
> <alex.williamson@xxxxxxxxxx> wrote:
> > On Fri, 2012-10-05 at 17:22 +0000, Blue Swirl wrote:
> >> On Fri, Oct 5, 2012 at 5:11 PM, Alex Williamson
> >> <alex.williamson@xxxxxxxxxx> wrote:
> >> > On Fri, 2012-10-05 at 16:54 +0000, Blue Swirl wrote:
> >> >> On Wed, Sep 26, 2012 at 5:19 PM, Alex Williamson
> >> >> <alex.williamson@xxxxxxxxxx> wrote:
> >> >> > +
> >> >> > +typedef struct QEMU_PACKED VFIOIRQSetFD {
> >> >> > + struct vfio_irq_set irq_set;
> >> >> > + int32_t fd;
> >> >> > +} VFIOIRQSetFD;
> >> >>
> >> >> I'm now getting this error from Clang:
> >> >>
> >> >> /src/qemu/hw/vfio_pci.c:126:25: error: field 'irq_set' with variable
> >> >> sized type 'struct vfio_irq_set' not at the end of a struct or class
> >> >> is a GNU extension [-Werror,-Wgnu]
> >> >> struct vfio_irq_set irq_set;
> >> >>
> >> >> Does the kernel really use the fd field, isn't it implicit from the
> >> >> ioctl fd or are they different?
> >> >
> >> > The kernel side is defined as:
> >> >
> >> > struct vfio_irq_set {
> >> > __u32 argsz;
> >> > __u32 flags;
> >> > __u32 index;
> >> > __u32 start;
> >> > __u32 count;
> >> > __u8 data[];
> >> > };
> >>
> >> Then the kernel only expects vfio_irq_set structure, not VFIOIRQSetFD,
> >> so you should use &irq_set_fd.irq_set instead of &irq_set_fd for the
> >> ioctl(). Then VFIOIRQSetFD can be rearranged to have fd field first,
> >> also QEMU_PACKED is not necessary.
> >
> > Sorry, I was unclear. The kernel sees fd as data[0], that's the point
> > of the structure, so re-arranging it makes it useless. Thanks,
>
> I see. The example in GCC shows how to statically initialize flexible
> array members properly but it does not seem to work:
> http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
That's not going to like that the data type is actually different for
this use case.
> Also, Clang does not like that syntax either.
>
> Maybe it's best to use g_malloc with room for the extra int.
:( Ok, I'll write a patch to make it dynamically allocated. Thanks,
Alex
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