On Thu, 23 Feb 2017 16:21:47 +0100 Paolo Bonzini <pbonz...@redhat.com> wrote:
> On 23/02/2017 15:35, Peter Maydell wrote: > > On 23 February 2017 at 12:53, Paolo Bonzini <pbonz...@redhat.com> wrote: > >> > >> > >> On 23/02/2017 13:26, Peter Maydell wrote: > >>> On 23 February 2017 at 11:43, Paolo Bonzini <pbonz...@redhat.com> wrote: > >>>> On 23/02/2017 12:34, Peter Maydell wrote: > >>>>> We should probably update the doc comment to note that the > >>>>> pointer is to host-endianness memory (and that this is not > >>>>> like normal RAM which is target-endian)... > >>>> > >>>> I wouldn't call it host-endianness memory, and I disagree that normal > >>>> RAM is target-endian---in both cases it's just a bunch of bytes. > >>>> > >>>> However, the access done by the MemoryRegionOps callbacks needs to match > >>>> the endianness declared by the MemoryRegionOps themselves. > >>> > >>> Well, if the guest stores a bunch of integers to the memory, which > >>> way round do you see them when you look at the bunch of bytes? > >> > >> You see them in whatever endianness the guest used. > > > > I'm confused. I said "normal RAM and this ramdevice memory are > > different", and you seem to be saying they're the same. I don't > > think they are (in particular I think with a BE guest on an > > LE host they'll look different). > > No, they look entirely the same. The only difference is that they go > through MemoryRegionOps instead of memcpy. Is this true for vfio use case? If we use memcpy we're talking directly to the device with no endian conversions. If we use read/write then there is an endian conversion in the host kernel.
