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From: "Blue Swirl" <blauwirbel@gmail.com>
Subject: Re: [Qemu-devel] [PATCH 1/6] Use IO port for qemu<->guest BIOS
	communication.
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To: qemu-devel@nongnu.org

On 8/24/08, Gleb Natapov <gleb@qumranet.com> wrote:
> Use PIO to get configuration info between qemu process and guest BIOS.

Could you make this a separate device, so that it could be used in
other machines? There is nothing PC-specific.

>  +static uint32_t bios_cfg_read(void *opaque, uint32_t addr)
>  +{
>  +    BIOSCfgEntry *e = &bios_params.entries[bios_params.entry];

You should use the opaque parameter and cast that to BIOSCfgState.

>  +    if (!e->data)
>  +        return 0;
>  +
>  +    return e->data[bios_params.cur_offset++ % e->len];

Instead of using modular arithmetic, zero should be returned for invalid values.

>  +static void bios_cfg_write(void *opaque, uint32_t addr, uint32_t value)
>  +{
>  +    bios_params.entry = value % BIOS_CFG_MAX_ENTRY;

Same here, its important for downward compatibility.

>  +    bios_cfg_add_data(BIOS_CFG_SIGNATURE, "QEMU", 4);

I'd add:
+    bios_cfg_add_data(BIOS_CFG_ID, 1, 4);