[U-Boot] [PATCH 2/2] efi_loader: set the dhcp ack received flag

[Patrick Wildt]

On Fri, Mar 23, 2018 at 08:04:27PM +0100, Heinrich Schuchardt wrote:
> On 03/23/2018 08:01 PM, Heinrich Schuchardt wrote:
> >>From 689ada7663efae5ef13d021f3266e081d1d53293 Mon Sep 17 00:00:00 2001
> > From: Patrick Wildt <patrick at blueri.se>
> > Date: Fri, 23 Mar 2018 15:38:48 +0100
> > Subject: [PATCH 2/2] efi_loader: set the dhcp ack received flag
> > 
> > The PXE object contains a flag that specifies whether or not a DHCP
> > ACK has been received.  This might be used by programs to find out
> > whether or not it is worth to read the DHCP information ot ouf our
> > object.
> > 
> 
> Why should we implement this change now without a consumer for the
> information?
> 
> > Signed-off-by: Patrick Wildt <patrick at blueri.se>
> > ---
> >  include/efi_api.h        | 4 +++-
> >  lib/efi_loader/efi_net.c | 4 +++-
> >  2 files changed, 6 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/efi_api.h b/include/efi_api.h
> > index 3ba650e57e..7dfa17f5c6 100644
> > --- a/include/efi_api.h
> > +++ b/include/efi_api.h
> > @@ -756,7 +756,9 @@ struct efi_pxe_packet {
> > 
> >  struct efi_pxe_mode
> >  {
> > -	u8 unused[52];
> > +	u8 unused1[9];
> > +	u8 dhcp_ack_received;
> 
> Why use a byte in the middle of the unused region?

The EFI Spec defines shared interfaces.  In this case u-boot implements
the PXE Base Code Protocol, and "struct efi_pxe_mode" is a definition
for a struct that is shared on the interface.  The struct is defined in
UEFI Spec 2.6 Chapter 23.3 as EFI_PXE_BASE_CODE_MODE.  In this struct,
theres a boolean called DhcpAckReceivd, which is the 10th member of the
struct.  Since booleans in EFI are defined to uint8_t, this means it's
the 10th byte starting from the beginning of the struct.  Since u-boot
does not define all of the members of the struct, the first 52 bytes are
"unused".  Since I am now accessing a field in the interface in the
middle of those 52 bytes, it is split up into a first set and a second
set of unused bytes, with the new dhcp_ack_received in the middle.
Thus, it's not just a simple byte in the middle of an unused region and
putting it somewhere else would violate the spec.

The consumer in this case would be the EFI Application being booted
using the "bootefi" command.

Please correct me if I'm wrong.

Best regards,
Patrick

> 
> Best regards
> 
> Heinrich
> 
> > +	u8 unused2[42];
> >  	struct efi_pxe_packet dhcp_discover;
> >  	struct efi_pxe_packet dhcp_ack;
> >  	struct efi_pxe_packet proxy_offer;
> > diff --git a/lib/efi_loader/efi_net.c b/lib/efi_loader/efi_net.c
> > index 8c5d5b492c..0b9c7b9345 100644
> > --- a/lib/efi_loader/efi_net.c
> > +++ b/lib/efi_loader/efi_net.c
> > @@ -332,8 +332,10 @@ int efi_net_register(void)
> >  	netobj->net_mode.max_packet_size = PKTSIZE;
> > 
> >  	netobj->pxe.mode = &netobj->pxe_mode;
> > -	if (dhcp_ack)
> > +	if (dhcp_ack) {
> >  		netobj->pxe_mode.dhcp_ack = *dhcp_ack;
> > +		netobj->pxe_mode.dhcp_ack_received = 1;
> > +	}
> > 
> >  	/*
> >  	 * Create WaitForPacket event.
> > 
>