On Thu, 23 Feb 2017 16:47:23 +0100 Paolo Bonzini <pbonz...@redhat.com> wrote:
> On 23/02/2017 16:39, Alex Williamson wrote: > > 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. > > But ramd MemoryRegionOps do not use file read/write, they use memory > read/write, so they talk directly to the device. Ah ha! Ding! ;) Sorry, I forgot that.
