Re: [Qemu-devel] [PATCH RFC] ps2: set the keybord output buffer size as the same as kernel

[Juan Quintela]

Gerd Hoffmann <address@hidden> wrote:
> On Mi, 2014-04-23 at 09:32 +0000, Gonglei (Arei) wrote:
>> > 
>> > Hi, Gerd and Juan.
>> > 
>> > Thanks for your guides about the confuse live migration about changing the
>> > keyboard buffer size.
>> > According your suggestion, I got two solutions to address the issue:
>> > 
>> > - Keep the data array 256 bytes long, change the
>> > rptr/wptr/count/data array at
>> > post_load(), both
>> >  Ps/2 keyboard and mouse. This solution can be compatible with older qemu
>> > versions, which can
>> >  do live migration each other.
>> > 
>> > -Change the data array to 16 bytes, still save as PS2_QUEUE_SIZE. Reset the
>> > rptr/wptr/count at
>> > post_load(), both ps/2 keyboard and mouse. Add VMSTATE_UNUSED(256-16) in
>> > struct vmstate_ps2_common.
>> > This solution just save the 16 bytes buffer and drop the rest, So we can't
>> > migrate vm to older qemu versions.
>> > But migration from old qemu to new qemu is ok.
>> > 
>> Sorry, the second solution also support cross-version live migration
>> each other.

> But you loose anything in the buffer when migrating from old -> new.

Anything bigger than 16bytes, no?  And that is the whole point that we
are talking about?  Or the 16bytes that we are using can be at any place
on the buffer?  If that is the case, I agree that the first option is
better for some versions.  Sorry for my missunderstanding.

Later, Juan.

PD.  No, I don't claim to understand how PS2 work at all.