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Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) dev
From: |
Alexander Graf |
Subject: |
Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device |
Date: |
Mon, 19 Jul 2010 11:13:38 +0200 |
On 19.07.2010, at 11:10, Gleb Natapov wrote:
> On Mon, Jul 19, 2010 at 11:02:54AM +0200, Alexander Graf wrote:
>>
>> On 19.07.2010, at 11:00, Gleb Natapov wrote:
>>
>>> On Mon, Jul 19, 2010 at 10:54:43AM +0200, Alexander Graf wrote:
>>>>
>>>> On 19.07.2010, at 10:48, Gleb Natapov wrote:
>>>>
>>>>>
>>>>>> Were there DMA capable devices back in ISA times? There must be. If so,
>>>>>> we can just take a look at what they do and do it similarly. Bus
>>>>>> mastering was a new thing for PCI, right?
>>>>>>
>>>>> I think IDE can be considered DMA capable ISA device, no? At least
>>>>> it works by writing to PIO ports and getting result into memory, but
>>>>> with interrupts and status bits and everything that real device should
>>>>> have. On board DMA engine is also ISA device.
>>>>
>>>> We could define our device to be polling. So all we need is a status bit
>>>> that the guest sets when it starts the DMA and the device unsets when the
>>>> DMA is done. In our case that should be immediate, because the PIO invokes
>>>> the full code paths, but it would look more like a real device, no?
>>>>
>>> This is better, but it shouldn't be synchronous. Kernel and initrd are
>>> on disk so why not setup aio and read them from io thread allowing vcpu
>>> thread immediately return to guest mode to process interrupts.
>>
>> That would work with the above described device model. If we're going
>> synchronous or asynchronous would become an implementation detail.
>>
> If vcpu thread will sleep for too much time without processing events we can
> see strange timeouts in a guest.
I don't think I understand what you mean?
>
>>> Or why
>>> not use virtio-serial while we are at it? After all virtio-serial is
>>> there to allow host and guest communication.
>>
>> Because virtio-serial needs us to set up the full virtio-pci stack. That's
>> too much to mess with in an option rom IMHO.
>>
> We already do it for virtio-blk. Read only support is very small in
> LOC there. Don't know about virtio-serial protocol.
The virtio-blk model uses the whole pxe framework. For our in-tree option roms
we're trying to be simple. And I'd like to keep it that way. I really don't
want to add PCI enumeration and BAR setup to that code.
Alex
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, (continued)
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Alexander Graf, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Gleb Natapov, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Alexander Graf, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Gleb Natapov, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Alexander Graf, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Gleb Natapov, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Alexander Graf, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Gleb Natapov, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Alexander Graf, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Gleb Natapov, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device,
Alexander Graf <=
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Gleb Natapov, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Alexander Graf, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Gleb Natapov, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Richard W.M. Jones, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Jamie Lokier, 2010/07/20
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Gleb Natapov, 2010/07/20
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Richard W.M. Jones, 2010/07/20
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Richard W.M. Jones, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Richard W.M. Jones, 2010/07/19
- Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device, Gleb Natapov, 2010/07/19