[Qemu-devel] Re: [PATCHv4 15/15] Pass boot device list to firmware.

[Gleb Natapov]

On Mon, Nov 15, 2010 at 09:52:19PM -0500, Kevin O'Connor wrote:
> On Mon, Nov 15, 2010 at 03:36:25PM +0200, Gleb Natapov wrote:
> > On Mon, Nov 15, 2010 at 08:26:35AM -0500, Kevin O'Connor wrote:
> > > On Mon, Nov 15, 2010 at 09:40:08AM +0200, Gleb Natapov wrote:
> > > > On Sun, Nov 14, 2010 at 10:40:33PM -0500, Kevin O'Connor wrote:
> > > > > Why not just return a newline separated list that is null terminated?
> > > > > 
> > > > Doing it like this will needlessly complicate firmware side. How do you
> > > > know how much memory to allocate before reading device list?
> > > 
> > > My preference would be for the size to be exposed via the
> > > QEMU_CFG_FILE_DIR selector.  (My preference would be for all objects
> > > in fw_cfg to have entries in QEMU_CFG_FILE_DIR describing their size
> > > in a reliable manner.)
> > > 
> > Will interface suggested by Blue will be good for you? The one with two
> > fw_cfg ids. BOOTINDEX_LEN for len and BOOTINDEX_DATA for device list. I
> 
> I dislike how different fw_cfg objects pass the length in different
> ways (eg, QEMU_CFG_E820_TABLE passes length as first 4 bytes).  This
> is a common problem - I'd prefer if we could adopt one uniform way of
> passing length.  I think QEMU_CFG_FILE_DIR solves this problem well.
>
Looking at available fw cfg option I see that _SIZE _DATA is also a
common pattern. The problem with QEMU_CFG_FILE_DIR is that we have very
little available slots right now. If we a going to require everything to
use it we better grow number of available slots considerably now while
it is easily done (no option defined above file slots yet).

I personally do not have preferences one way or the other. Blue are you
OK with using QEMU_CFG_FILE_DIR?

> I also have an ulterior motive here.  If the boot order is exposed as
> a newline separated list via an entry in QEMU_CFG_FILE_DIR, then this
> becomes free for coreboot users as well.  (On coreboot, the boot order
> could be placed in a "file" in flash with no change to the seabios
> code.)
> 
You can define get_boot_order() function and implement it differently
for qemu and coreboot. For coreboot it will be one linear. Just call
cbfs_copyfile("bootorder"). BTW why newline separation is important? 

--
                        Gleb.