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Re: [Xen-devel] [PATCH] libxl: Specify the target ram size to Qemu (new)

To: Keir Fraser <keir@xxxxxxx>
Subject: Re: [Xen-devel] [PATCH] libxl: Specify the target ram size to Qemu (new) when calling it
From: Anthony PERARD <anthony.perard@xxxxxxxxxx>
Date: Thu, 6 Jan 2011 15:12:51 +0000 (GMT)
Cc: Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
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On Thu, 6 Jan 2011, Keir Fraser wrote:

> On 06/01/2011 14:28, "Ian Jackson" <Ian.Jackson@xxxxxxxxxxxxx> wrote:
> > anthony.perard@xxxxxxxxxx writes ("[Xen-devel] [PATCH] libxl: Specify the
> > target ram size to Qemu (new) when calling it"):
> >> This patch adds target_ram in device_model_info structure, to be used in
> >> libxl_build_device_model_args_new. Qemu upstream needs to know about it.
> >
> > I have applied this patch, thanks.
> >
> > I'm just a little concerned, though: can you explain _why_ qemu
> > upstream needs to know the target ram size ?
> Qemu used to be responsible for initialising BIOS info tables, including
> memory size information such as e820, in lieu of the virtual BIOS doing it.
> I ripped all that out from our diverged tree, and put it in
> hvmloader/rombios, but maybe they still do it in upstream qemu. I think it
> would be harmless if so, since hvmloader/rombios will overwrite/ignore.

There are another reason, qemu "allocate" the memory for the vga at a
dynamic address. In qemu-xen, this address is static. So qemu need to
know the size of the ram to put the memory of the vga after the ram.
Qemu do the same for other memory like the rom of a nic.

Information about the ram is put in the struct RAMBlock of qemu.

Anthony PERARD

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