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


From: Gonglei (Arei)
Subject: Re: [Qemu-devel] [PATCH RFC] ps2: set the keybord output buffer size as the same as kernel
Date: Wed, 23 Apr 2014 13:01:15 +0000

> 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.
> 
Actually, in my hundreds of times testing, about the queue buffer value, at the 
migration dest end
the rptr always equal with wptr, the value range is [0, 256), and count value 
always is 0.
So, in the old qemu versions, the 16 bytes data maybe at any place on the 
buffer. The queue just be 
realized to a lined container by data array, the rptr/wptr will fill it 
cyclically. 

So, I want to post a normal patch about the first solution, can I? Thanks.


Best regards,
-Gonglei



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