Re: [Qemu-devel] [RFC] New device API

[Anthony Liguori <anthony@codemonkey.ws>]

Paul Brook wrote:
> On Wednesday 06 May 2009, Paul Brook wrote:
>   
>>>> The attached patch is my attempt at a new internal API for device
>>>> creation in qemu.
>>>>         
>>> Instead of recreating constructors, I think we should just use GCC's
>>> constructor attribute.  This gives us ordering which will be important
>>> when dealing with buses.
>>>       
>> The reason I'm not using constructors is because you have to workaround
>> ordering issues. All constructors are run before main(), so there's a very
>> limited amount they can actually do, and constructor priorities are not
>> available on all hosts.
>>     

I was going to make an argument that you want to have multiple 
constructors in a single file.  However, I think this is wrong.  I think 
you want to make sure that you only register one device per file.

> Oh, the other thing is that constructors don't work when you put objects in a 
> static library.  You need am explicit dependency to pull in objects.
>   

I think I'd be happier if we just made it a little less connected.  So, 
something like:

static DeviceType *qdev_register(const char *name, int size, qdev_initfn init,
                                 void *opaque)
{
}

device_init(qdev_register);

Then:

#! /bin/sh
# Call device init functions.

file="$1"
shift
devices="$@"
echo '/* Generated by gen_devices.sh */' > $file
echo '#include "sysemu.h"' >> $file
echo "void register_devices(void)" >> $file
echo "{" >> $file
for x in $devices ; do
    sed -e 's:$device_init(\(.*)\);$:#qdevice \1:g' | grep '#qdevice' | cut -f2- -d' ' | while read DEVICE_INIT; do
        echo "{ extern void qemu_do_device_init_${DEVICE_INIT}(void); qemu_do_device_init_${DEVICE_INIT}(); }"
    done
done
echo "}" >> $file

And:

#define device_init(func) \
void qemu_do_device_init ## func (void) { \
    func(); \
}

This requires that device_init() functions always are unique names.  It also means we can switch to constructors down the road if we wanted to and that problem goes away.  Also, it introduces a saner way to introduce priority.  We can have device_init(), pci_device_init(), virtio_device_init(), etc.

I haven't tried any of this code BTW.

Regards,

Anthony Liguori


> Paul
>
>
>