Re: [PATCH] KVM: PPC: Book3S HV: return htab entries in big endian

[Alexey Kardashevskiy <aik@ozlabs.ru>]

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On 10/04/2014 07:05 AM, Alexander Graf wrote:
> 
> 
> 
>> Am 03.10.2014 um 14:05 schrieb Paul Mackerras <paulus@samba.org>:
>> 
>>> On Thu, Oct 02, 2014 at 07:06:40PM +0200, Alexander Graf wrote:
>>> 
>>> I think we're best off to keep the user space API native endian.
>>> So really we should only ever have to convert from big to native
>>> endian on read and native to big on write.
>>> 
>>> With that QEMU should do the "right thing" already, no?
>> 
>> I believe that when migrating a guest, QEMU just passes the byte 
>> stream it gets from the htab fd along to the destination QEMU with 
>> little or no interpretation, and the destination QEMU writes the
>> byte stream to the htab fd for the receiving VM. Alexey would be
>> able to say for sure.
>> 
>> If that's the case, then perhaps it's best to define that byte
>> stream to contain values of one specific endianness, and for
>> compatibility that would be big endian.
>> 
>> I assume we would want to be able to migrate a guest from a BE host 
>> to an LE host or vice versa. If not then the question is moot.
> 
> Yes, the migration stream needs to stay host endian agnostic, so it 
> should be BE. Whether QEMU or kvm does the conversion is an 
> implementation detail I don't mind much for either way.


I find it lot easier if every binary interface has defined endianness,
using native endian just creates problems.


> But keep in mind that qemu also uses the htab fd for htab
> introspection that it does for gdbstub emulation or the x monitor
> command.


- -- 
Alexey
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