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

[Gerd Hoffmann]

On Mi, 2014-04-23 at 11:45 +0200, Juan Quintela wrote:
> "Gonglei (Arei)" <address@hidden> 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.
> 
> Second solution is better in the sense that it allows forward and
> backward migration.   The first one only allows forward migration.

No, first goes both ways too, and unlike the second it doesn't loose the
buffer content as long as less than 16 bytes are actually used.

cheers,
  Gerd