Re: [Xen-devel] virtual bios question

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2011-05-26 at 14:15 +0100, Daniel Castro wrote:
> CC the mail List.
> 
> 
> 
> On Thu, May 26, 2011 at 9:18 PM, henanwxr <henanwxr@xxxxxxxxxxx> wrote:
> > Hi, thank you for your reply, but I am not very clear. Can you explain in 
> > detail?
> > Do you mean qemu-dm don't execute the virtual bios?
> > But in my opinion, a plain qemu emulator will execute the virtual bios in 
> > its initialization, when qemu-dm work with hvmloader, how does qemu-dm  
> > ignore the execution of its virtual bios?
> 
> The Virtual BIOS is not something you execute per se. qemu-dm is the
> executable, it loads the memory with a binary blob,

strictly speaking it is the domain builder which loads things into
memory, qemu-dm doesn't have anything to do with it.

In a xen system qemu only provides emulation for devices, qemu's code
execution functionality is unused in this context.

>  that binary blob
> is hvmloader (hvmloader has more functions, this is one), inside
> hvmloader is another binary blob that is rombios, the virtual BIOS.
> After all this is loaded to the memory the balloon driver reserved the
> bootloader quicks in using the BIOS and the emulated ide disk provided
> by qemu but interfaced through the virtual BIOS, the bootloader
> process starts, it reads the boot sector 0 from the emulated disk and
> jumps to the bootstrap just like a regular boot sequence. The loading
> HVM Kernel sees memory as if it were the only system running on the
> machine because it sees memory starting from 0, the BIOS is located at
> 0x00000400. When in fact it resides somewhere in main memory (not
> starting from 0) that is controlled by the dom0.
> 
> Some of the boot steps are missing.
> 
> Daniel
> 
> >
> >
> >
> > --------------------------------------------------
> > From: "Daniel Castro" <evil.dani@xxxxxxxxx>
> > Sent: Thursday, May 26, 2011 5:26 PM
> > To: "confucius" <henanwxr@xxxxxxxxxxx>
> > Subject: Re: [Xen-devel] virtual bios question
> >
> >> As I understand it, please se below:
> >>
> >>
> >>
> >> On Thu, May 26, 2011 at 2:16 PM, confucius <henanwxr@xxxxxxxxxxx> wrote:
> >>> Hi, when user create the virtual machine, then:
> >>> which code execute firstly, hvmloaer or qemu-dm?I have traced the codes 
> >>> flow
> >>> and found qemu-dm run before hvmloader,right?
> >>>
> >>> And virtual bios code are both in hvmloader and qemu-dm, but I think it
> >>> should be only one of virtual bios
> >>> will be used to initialize the virutal device in qemu-dm.I find at the end
> >>> of hvmloader it will jmp to 0xffff0, that is the bios entry,so I think  
> >>> the
> >>> virtual bios in hvmloader will function. But how qemu-dm ingore the
> >>> execution of its virual bios inside?
> >>>
> >>> Any one help me? Thanks.
> >>
> >> When the domain builder is called, it created the qemu-dm in
> >> userspace, the baloon driver for memory is called to reserve the
> >> necesary memory. Qemu uses hvmloader to create the necesary
> >> information for a machine to boot (hvmloader is the payload for qemu),
> >> the BIOS is included as a binary blob inside hvmloader. So for
> >> example, the BIOS binary image will me found in the expected memory
> >> address as well as ACPI tables and all the usual things that a
> >> baremetal machine would find.
> >> Both hvmloader and qemu work in concert to make the BIOS work. then
> >> the BIOS calls the bootloader in the primary IDE device provided by
> >> qemu, this can be changed with configurations options.
> >>
> >> Hope this helps.
> >>
> >> Daniel
> >>>
> >>>
> >>> --
> >>> View this message in context: 
> >>> http://xen.1045712.n5.nabble.com/virtual-bios-question-tp4427579p4427579.html
> >>> Sent from the Xen - Dev mailing list archive at Nabble.com.
> >>>
> >>> _______________________________________________
> >>> Xen-devel mailing list
> >>> Xen-devel@xxxxxxxxxxxxxxxxxxx
> >>> http://lists.xensource.com/xen-devel
> >>>
> >>
> >>
> >>
> >> --
> >> +-=====---------------------------+
> >> | +---------------------------------+ | This space intentionally blank
> >> for notetaking.
> >> | |   | Daniel Castro,                |
> >> | |   | Consultant/Programmer.|
> >> | |   | U Andes                         |
> >> +-------------------------------------+
> >>
> 
> 
> 
> -- 
> +-=====---------------------------+
> | +---------------------------------+ | This space intentionally blank
> for notetaking.
> | |   | Daniel Castro,                |
> | |   | Consultant/Programmer.|
> | |   | U Andes                         |
> +-------------------------------------+
> 
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