Re: [Qemu-devel] Slow kernel/initrd loading via fw_cfg; Was Re: Hack integrating SeaBios / LinuxBoot option rom with QEMU trace backends

[Kevin O'Connor]

On Tue, Oct 11, 2011 at 08:17:28AM -0500, Anthony Liguori wrote:
> On 10/11/2011 04:55 AM, Avi Kivity wrote:
> >On 10/11/2011 11:50 AM, Gleb Natapov wrote:
> >>But loading MBs of data through fw_cfg interface is just abusing it.
> >>You wouldn't use pio on real HW to move megabytes of data and expect
> >>good performance.
> >
> >True, this is a point in favour of a true dma interface.
> 
> Doing kernel loading through fw_cfg has always been a bit ugly.
> 
> A better approach would be to implement a PCI device with a ROM bar
> that contained an option ROM that read additional bars from the
> device to get at the kernel and initrd.

If one is willing to add a PCI device, then one could add a virtio
block device with a non-standard PCI device/vendor code and teach
SeaBIOS to scan these non-standard ids.  It's a bit of a hack, but it
would be a simple way of creating a drive visible by the bios but
hidden from the OS.

-Kevin