On 08/04/2010 12:31 PM, Alexander Graf wrote:
On 04.08.2010, at 19:26, Anthony Liguori wrote:
On 08/04/2010 11:45 AM, Alexander Graf wrote:
Frankly, I partially agreed to your point when we were talking about 300ms vs. 2 seconds. Now that we're talking 8 seconds that whole point is moot. We chose the wrong interface to transfer kernel+initrd data into the guest.
Now the question is how to fix that. I would veto against anything normally guest-OS-visible. By occupying the floppy, you lose a floppy drive in the guest. By occupying a disk, you see an unwanted disk in the guest.
Introduce a new virtio device type (say, id 6). Teach SeaBIOS that 6 is exactly like virtio-blk (id 2). Make it clear that id 6 is only to be used by firmware and that normal guest drivers should not be written for id 6.
Why not make id 6 be a fw_cfg virtio interface?
Because that's a ton more work and we need fw_cfg to be available before
PCI is. IOW, fw_cfg cannot be a PCI interface.
Regards,
Anthony Liguori
That way we'd stay 100% compatible to everything we have and also get a fast path for reading big chunks of data from fw_cfg. All we'd need is a command to set the 'file' we're in.
Even better yet, why not use virtio-9p and expose all of fw_cfg as files? Then implement a simple virtio-9p client in SeaBIOS and maybe even get direct kernel/initrd boot from a real 9p system ;).
Alex
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