Re: [PATCH] ArmPkg/PlatformBootManagerLib: regenerate boot options on boot failure

["Leif Lindholm" <leif@nuviainc.com>]

On Wed, Jun 17, 2020 at 14:59:45 +0200, Ard Biesheuvel wrote:
> > > > Something like:
> > > > "On entry, the UiApp instantiates the autogenerated boot options that
> > > > we used to rely on - but it does not consume them. This breaks the
> > > > unattended..."
> > > 
> > > OK
> > > 
> > > > I assume the UiApp only ever *adds* entries, which is why checking
> > > > number of entries is sufficient?
> > > > 
> > > 
> > > It only manages entries that it instantiated itself, but it may also remove
> > > entries if the underlying hardware has disappeared.
> > 
> > Hmm, that's a bit trickier then. I mean, it's unlikely, but I'm sure
> > there's situations that could happen.
> > Would we run the risk of getting bug reports like "system fails to
> > boot from Ethernet when inifiniband switch powered off"? Or if some
> > virtual devices presented by a BMC appear/disappear?
> > 
> 
> If the boot entries are not refreshed, you will retain the old ones. So the
> only way this could lead to a boot failure is when you rely on automatically
> generated boot entries to device that disappear and reappear in a different
> place, e.g., move a Ethernet PCIe card to a different slot. Note that USB
> devices plugged into a different port will still work fine, though, as they
> rely on the removable boot path in this case, which will be attempted anyway
> before doing the UnableToBoot().
> 
> Note that the failure mode here is being dropped into the menu, where before
> you were always dropped into the Shell. The case we are trying to address
> here is zero intervention network boot after putting the device into
> circulation, and that should work correctly with this change: if the network
> boot path did not exist before, it will be added, in which case the number
> of boot options will increase.

OK. I'm not convinced we're not going to see a report of this
somewhere down the line, but I think you've managed to convince me
it's an unlikely enough situation, and a fallback, that we can bump it
to then (and it *is* a behavioural improvement in all other cases).

Reviewed-by: Leif Lindholm <leif@nuviainc.com>
(with the commit message update)

/
    Leif