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Subject: Re: [Qemu-devel] Multi-head support RFC
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To: Gerd Hoffmann <kraxel@redhat.com>
Cc: qemu-devel@nongnu.org

On 11/19/2013 1:57 AM, Gerd Hoffmann wrote:
>    Hi,
>
>> I think it would be better if the HwOps calls all took a QemuConsole
>> instead of the opaque structure. The hw implementations can dig their
>> opaque structure out from there.
> QemuConsole is private to ui/console.c though (and I prefer to keep it
> this way).  So we need either a helper function to query con->hw or we
> keep the opaque and pass QemuConsole as additional parameter.
>
> When going this route.
>
> Alternative approach:
>
> struct my_gfx_card_state {
>      PCIDevice pci;
>      [ ... ]
>      struct my_head_state {
>          QemuConsole *con;
>          [ ... ]
>      } heads[MAX_HEADS];
> }
>
> Then instead of
>
>     graphic_console_init(..., &state);
>
> call
>
>     graphic_console_init(..., &state->heads[i]);
>
> so you can figure the head in the callbacks.

What I had prototyped (I got impatient) was to add a helper: 
qemu_console_hw_opaque() to console.c so the HwOps could query the 
opaque pointer. I don't like it because it requires an additional 
function call at the top of frequently called operations... However I'm 
not a huge fan of the head state array either, since it will require 
either pointer duplication, or pointer acrobatics, or the same helper 
function to get the card state.

A third option would be to use the console index as a parameter to each 
HwOp. graphic_console_init and QemuConsole could remain unchanged, as 
could all the graphic_hw_*() helpers. If the HwOp needs the QemuConsole 
for any given operation, it could then use 
qemu_console_lookup_by_index(). Many operations would only need the 
index though.

> cheers,
>    Gerd
>
>
>