Re: [Qemu-devel] [PATCH 1/2] pc: add etc/e820 fw_cfg file

[Gerd Hoffmann]

On Di, 2013-11-05 at 18:48 +0100, Andrea Arcangeli wrote:
> Hi,
> 
> On Mon, Nov 04, 2013 at 01:17:10PM +0100, Gerd Hoffmann wrote:
> > Unlike the existing FW_CFG_E820_TABLE entry which carries reservations
> > only the new etc/e820 file also has entries for RAM.
> 
> Acked, it looks the best the way to go if the objective is to keep
> backwards compatibility with older seabios protocol.
> 
> I have to trust you on why we need to stay backwards compatible at all
> times and why we can't commit an updated bios.bin before a new seabios
> stable release happened.

It's seabios policy, for good reasons.  Basically because it is a PITA
in certain cases if there are strict version requirements.  Also note
that seabios isn't the only possible firmware for qemu.

> About the file, I wonder what happens if too many people starts to use
> files and we'll run out of FW_CFG_FILE_SLOTS at runtime (assert(index
> < FW_CFG_FILE_SLOTS);).

Probably we should simply raise the number of slots.  We don't have
allocated any FW_CFG slots behind the file slot range yet, so there is
space.  Also there is a count in the file list struct and firmware uses
that to figure how many files are there and dynamically allocate memory
for the list, so growing the list shouldn't cause problems on the
firmware side too.

> Probably one patch could be added to
> s/FW_CFG_E820_TABLE/FW_CFG_E820_TABLE_OLD/, otherwise if somebody read
> fw_cfg.h, it won't be apparent that the grepping shouldn't stop there
> to reach the real e820 map.

Yep, either that or a comment.  Also there are more obsolete fw_cfg
entries I think.  Isn't the num_cpus entry superseded by numa info?

cheers,
  Gerd