Re: [Qemu-devel] fw cfg files cross-version migration races

[Michael S. Tsirkin]

On Mon, Jun 08, 2015 at 09:32:53AM -0400, Gabriel L. Somlo wrote:
> On Mon, Jun 08, 2015 at 02:33:45PM +0200, Gerd Hoffmann wrote:
> >  Hi,
> > 
> > > I'm wonderingjust when exactly to start sorting items in fw_cfg ? 
> > 
> > I'd suggest to sort as entries are added, i.e. just insert the new entry
> > at the correct place instead of tacking it to the end.  So the list is
> > always sorted.
> 
> I was thinking that too, but since these are all arrays (not linked
> lists), I'm a bit put off by the idea of having to shift everything
> that's already in there by one position upon each "sorted insert".
> Not to mention updating the "select" field of each FWCfgFile entry in
> the directory (and maybe sorting/shifting the FWCfgFiles directory
> itself) :(
> 
> Combined with "only do this on machine versions 2.4 or later", maybe
> just sorting everything during the machine_ready callback would be
> less hairy ?

Unfortunately we have a bunch of code adding fw cfg entries
after machine ready.

> I'll be on vacation for one week, so meditating on this in the back
> of my mind might help come up with something... :)
> 
> Thanks,
> --Gabriel