Re: [2.02][PATCH] bootp: export server IP as environment variable

[Daniel Kiper]

On Mon, Nov 21, 2016 at 10:52:24PM +0300, Andrei Borzenkov wrote:
> 21.11.2016 16:09, Daniel Kiper ??????????:
> > On Fri, Nov 18, 2016 at 09:11:47PM +0300, Andrei Borzenkov wrote:
> >> 17.11.2016 22:02, Daniel Kiper ??????????:
> >>> On Fri, Mar 18, 2016 at 08:42:00PM +0300, Andrei Borzenkov wrote:
> >>>> Network boot autoconfiguration sets default server to next server IP
> >>>> (siaddr) from BOOTP/DHCP reply, but manual configuration using net_bootp
> >>>> exports only server name. Unfortunately semantic of server name is not
> >>>> clearly defined. BOOTP RFC 951 defines it only for client request, and
> >>>> DHCP RFC 1541 only mentions it, without any implied usage. It looks like
> >>>> this field is mostly empty in server replies.
> >>>>
> >>>> Export next server IP as net_<interface>_server_ip variable. This allows
> >>>> grub configuration script to set $root/$prefix based on information 
> >>>> obtained
> >>>> by net_bootp.
> >>>>
> >>>> Reported and tested by: Nikunj A Dadhania <address@hidden>
> >>>> Cc: address@hidden
> >>>>
> >>>> ---
> >>>>
> >>>> @Nikunj: cosmetic changes comparing with version you tested - no need to
> >>>> allocate small buffer dynamically.
> >>>>
> >>>> @Vladimir: I think this is useful; I will update networking documentation
> >>>> in followup patch.
> >>>
> >>> Vladimir, Andrei, could you take care of it?
> >>>
> >>> Daniel
> >>>
> >>
> >> I added documentation (not worth separate patch); if there are no
> >> objections I commit.
> >>
> >>
> >> From: Andrei Borzenkov <address@hidden>
> >> Subject: [2.02][PATCH] bootp: export server IP as environment variable
> >>
> >> Network boot autoconfiguration sets default server to next server IP
> >> (siaddr) from BOOTP/DHCP reply, but manual configuration using net_bootp
> >> exports only server name. Unfortunately semantic of server name is not
> >> clearly defined. BOOTP RFC 951 defines it only for client request, and
> >> DHCP RFC 1541 only mentions it, without any implied usage. It looks like
> >> this field is mostly empty in server replies.
> >>
> >> Export next server IP as net_<interface>_server_ip variable. This allows
> >> grub configuration script to set $root/$prefix based on information 
> >> obtained
> >> by net_bootp.
> >>
> >> Reported and tested by: Nikunj A Dadhania <address@hidden>
> >> Cc: address@hidden
> >>
> >> ---
> >>  docs/grub.texi        | 11 +++++++++++
> >>  grub-core/net/bootp.c | 24 ++++++++++++++----------
> >>  2 files changed, 25 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/docs/grub.texi b/docs/grub.texi
> >> index 82f6fa4..bb03875 100644
> >> --- a/docs/grub.texi
> >> +++ b/docs/grub.texi
> >> @@ -2446,6 +2446,10 @@ The boot file name provided by DHCP.  Read-only.
> >>  The name of the DHCP server responsible for these boot parameters.
> >>  Read-only.
> >>
> >> address@hidden address@hidden<interface>}_server_ip
> >> +The IP address of the next (usually, TFTP) server provided by DHCP.
> >
> > BOOTP instead of DHCP? However, then we should change DHCP everywhere too...
> >
>
> Yes. Sorry, it was probably my fault to refer to DHCP in the first place.
>
> >> +Read-only.
> >> +
> >>  @item net_default_interface
> >>  Initially set to name of network interface that was used to load grub.
> >>  Read-write, although setting it affects only interpretation of
> >> @@ -3062,6 +3066,7 @@ These variables have special meaning to GRUB.
> >>  * address@hidden<interface>}_hostname::
> >>  * address@hidden<interface>}_ip::
> >>  * address@hidden<interface>}_mac::
> >> +* address@hidden<interface>}_server_ip::
> >
> > There is something known as net_default_server which contains next IP 
> > address.
> > Should not we be more consistent and use 
> > "address@hidden<interface>}_server" instead
> > of "address@hidden<interface>}_server_ip" here and there.
> >
>
> Well, net_default_server is not really tied to any BOOTP/DHCP at all,
> although it may be initially set based on content of ACK packet. I was
> confused by dhcp_server_name, but they it is unrelated to next server.
>
> I'd rather used net_<interface>_next_server for clarity, both "server"
> and "server_ip" are indeed too vague in this case.

net_<interface>_next_server is OK for me. Should not we introduce
net_default_next_server as RO then too? At first its value will be
equal net_default_server but only net_default_server could be
changed by user. Does it make sense?

Daniel