On 11/10/13 15:50, Will Deacon wrote:
> On Fri, Oct 11, 2013 at 03:36:30PM +0100, Marc Zyngier wrote:
>> Wrap all accesses to virt_queue data structures shared between
>> host and guest with byte swapping helpers.
>>
>> Should the architecture only support one endianness, these helpers
>> are reduced to the identity function.
>>
>> Cc: Pekka Enberg <penberg@xxxxxxxxxx>
>> Cc: Will Deacon <will.deacon@xxxxxxx>
>> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
>> ---
>> tools/kvm/include/kvm/virtio.h | 189 ++++++++++++++++++++++++++++++++++++++++-
>> tools/kvm/virtio/core.c | 59 +++++++------
>> 2 files changed, 219 insertions(+), 29 deletions(-)
>>
>> diff --git a/tools/kvm/include/kvm/virtio.h b/tools/kvm/include/kvm/virtio.h
>> index d6b0f47..04ec137 100644
>> --- a/tools/kvm/include/kvm/virtio.h
>> +++ b/tools/kvm/include/kvm/virtio.h
>> @@ -1,6 +1,8 @@
>> #ifndef KVM__VIRTIO_H
>> #define KVM__VIRTIO_H
>>
>> +#include <endian.h>
>> +
>> #include <linux/virtio_ring.h>
>> #include <linux/virtio_pci.h>
>>
>> @@ -29,15 +31,194 @@ struct virt_queue {
>> u16 endian;
>> };
>>
>> +/*
>> + * The default policy is not to cope with the guest endianness.
>> + * It also helps not breaking archs that do not care about supporting
>> + * such a configuration.
>> + */
>
> Jesus Marc, are you *trying* to crash my preprocessor? Seriously though,
> maybe this is better done as a block:
>
> #if __BYTE_ORDER == __BIG_ENDIAN
> #define virtio_le16toh(x) le16toh(x)
> #define virtio_be16toh(x)
> [...]
>
The preprocessor magic to turn the functions into one-liners is pretty
gruesome in itself, though...
>> +#ifndef VIRTIO_RING_ENDIAN
>> +#define VIRTIO_RING_ENDIAN 0
>> +#endif
>> +
>> +#if (VIRTIO_RING_ENDIAN & ((1UL << VIRTIO_RING_F_GUEST_LE) | (1UL << VIRTIO_RING_F_GUEST_BE)))
>> +
>> +#ifndef __BYTE_ORDER
>> +#error "No byteorder? Giving up..."
>> +#endif
#ifdef __BYTE_ORDER
#if __BYTE_ORDER == __BIG_ENDIAN
#define BYTEORDER_TOKEN be
#define ENDIAN_OPPOSITE VIRTIO_ENDIAN_LE
#else
#define BYTEORDER_TOKEN le
#define ENDIAN_OPPOSITE VIRTIO_ENDIAN_BE
#endif
#define _CAT3(a,b,c) a##b##c
#define CAT3(a,b,c) _CAT3(a,b,c)
#define vio_gtoh(size, val) (endian==ENDIAN_OPPOSITE) ?\
CAT3(BYTEORDER_TOKEN,size,toh(val)) : val
#define vio_htog(size, val) (endian==ENDIAN_OPPOSITE) ?\
CAT3(hto,BYTEORDER_TOKEN,size(val)) : val
#else
#error "No byteorder? Giving up..."
#endif
>> +
>> +
>> +static inline __u16 __virtio_guest_to_host_u16(u16 endian, __u16 val)
>> +{
>> +#if __BYTE_ORDER == __BIG_ENDIAN
>> + if (endian == VIRTIO_ENDIAN_LE)
>> + return le16toh(val);
>> +#else
>> + if (endian == VIRTIO_ENDIAN_BE)
>> + return be16toh(val);
>> +#endif
{
return vio_gtoh(16, val);
}
On the upside however, it does remove all the duplication and keep all
the mess in one place.
Robin.
>
> Then you can just use the endian parameter to do the right thing.
>
> Will
>
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