Re: Obtaining the MAC address of the boot NIC for a PXE boot

[Rigoberto Corujo]

----- Original Message -----

> From: Andrey Borzenkov <address@hidden>
> To: Rigoberto Corujo <address@hidden>
> Cc: "address@hidden" <address@hidden>; address@hidden
> Sent: Wednesday, May 1, 2013 10:59 AM
> Subject: Re: Obtaining the MAC address of the boot NIC for a PXE boot
> 
> В Mon, 29 Apr 2013 05:55:32 -0700 (PDT)
> Rigoberto Corujo <address@hidden> пишет:
> 
>>  Hello everyone,
>> 
>>  With pxelinux, you can specify "IPAPPEND 2" in your boot loader 
> configuration file and the MAC address of the boot NIC automatically gets 
> appended to your kernel parameters as "BOOTIF=XX:XX:XX:XX:XX:XX". 
>> 
>>  I am now trying to become familiar with Grub 2, because if its EFI support. 
>   I noticed that with Grub 2, some of the documentation, which may be 
> outdated, 
> says that there is a "net_pxe_mac" variable which, as I understand it, 
> should contain the MAC address of the boot NIC.  However, I've built the 
> latest Grub 2 sources and, when I PXE boot and drop into a grub shell prompt, 
> if 
> type "set", I don't see "net_pxe_mac" listed as one of 
> the variables.  I know there is a "net_ls_addr" command which prints 
> out something like "efinet8 3c:4a:92:b2:6a:e8 10.1.1.114", but I 
> don't know how to use Grub scripting to parse out the MAC address.  I also 
> don't know if there will ever be a case where "net_ls_addr" will 
> print out multiple entries on a PXE boot, making it difficult to determine 
> which 
> one corresponds to the boot NIC.
>> 
>> 
>>  Basically, I'm using the "ksdevice=bootif" kernel parameter 
> when PXE booting my Red Hat kernel.  With PXE Linux, "bootif" provides 
> the MAC address of the boot NIC.  I was hoping to do something like 
> "ksdevice=${net_pxe_mac}", but since "net_pxe_mac" does not 
> appear to be getting set, I need to find some other method.
>> 
> 
> 
> As it stands currently, net_pxe_* variables are defined on PC BIOS
> platform only. For UEFI (which you apparently have) GRUB2 defines
> net_efinetNN_* variables where efinetNN is symbolic name for interface
> that was used to boot GRUB2.
> 
> May be GRUB2 should also define net_pxe_* namespace for the case of
> UEFI. There is no real way to find out which interface was used for
> booting and even if there were, grub does not support nested
> variables substitution or eval'ing (like ${net_${boot_if}_mac).
> 
> Probably, adding "eval" support is really the most simple. Could you
> test the patch below. What it does, is
> 
> - it adds "eval" command (same as known from UNIX shells) which
>   executes its argument
> 
> - it exports boot interface as "efi_boot_interface" variable
> 
> This should allow you to do
> 
> if $grub_platform = efi ; then
>   eval "set net_pxe_mac=\$net_${efi_boot_interface}_mac" 
> fi
> 
> and then use $net_pxe_mac on both platforms.
> 
> If it works for you, I will clean it up; for consistency this is
> probably needed for ieee1275 as well.
> 
> ---
> grub-core/Makefile.core.def        |  5 ++++
> grub-core/commands/eval.c          | 51 ++++++++++++++++++++++++++++++++++++++
> grub-core/net/drivers/efi/efinet.c |  2 ++
> 3 files changed, 58 insertions(+)
> 
> diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
> index 7e19acb..8844f2f 100644
> --- a/grub-core/Makefile.core.def
> +++ b/grub-core/Makefile.core.def
> @@ -699,6 +699,11 @@ module = {
> };
> 
> module = {
> +  name = eval;
> +  common = commands/eval.c;
> +};
> +
> +module = {
>    name = extcmd;
>    common = commands/extcmd.c;
>    common = lib/arg.c;
> diff --git a/grub-core/commands/eval.c b/grub-core/commands/eval.c
> new file mode 100644
> index 0000000..a21ff89
> --- /dev/null
> +++ b/grub-core/commands/eval.c
> @@ -0,0 +1,51 @@
> +/*
> + *  GRUB  --  GRand Unified Bootloader
> + *  Copyright (C) 2009  Free Software Foundation, Inc.
> + *
> + *  GRUB is free software: you can redistribute it and/or modify
> + *  it under the terms of the GNU General Public License as published by
> + *  the Free Software Foundation, either version 3 of the License, or
> + *  (at your option) any later version.
> + *
> + *  GRUB is distributed in the hope that it will be useful,
> + *  but WITHOUT ANY WARRANTY; without even the implied warranty of
> + *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + *  GNU General Public License for more details.
> + *
> + *  You should have received a copy of the GNU General Public License
> + *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <grub/dl.h>
> +#include <grub/misc.h>
> +#include <grub/extcmd.h>
> +#include <grub/i18n.h>
> +#include <grub/term.h>
> +
> +GRUB_MOD_LICENSE ("GPLv3+");
> +
> +static grub_err_t
> +grub_cmd_eval (grub_extcmd_context_t ctxt __attribute__((__unused__)),
> +           int argc, char *argv[])
> +{
> +  char *dummy[1] = { NULL };
> +
> +  if (argc != 1)
> +    return  grub_error (GRUB_ERR_BAD_ARGUMENT, N_("one argument 
> expected"));
> +  return grub_script_execute_sourcecode (argv[0], 0, dummy);
> +}
> +
> +static grub_extcmd_t cmd;
> +
> +GRUB_MOD_INIT(eval)
> +{
> +  cmd = grub_register_extcmd ("eval", grub_cmd_eval, 0,
> +                  N_("[STRING]"), N_("Evaluate commands"),
> +                              NULL);
> +}
> +
> +GRUB_MOD_FINI(eval)
> +{
> +  grub_unregister_extcmd (cmd);
> +}
> +
> diff --git a/grub-core/net/drivers/efi/efinet.c 
> b/grub-core/net/drivers/efi/efinet.c
> index 2b344d6..f7d8fd5 100644
> --- a/grub-core/net/drivers/efi/efinet.c
> +++ b/grub-core/net/drivers/efi/efinet.c
> @@ -23,6 +23,7 @@
> #include <grub/efi/api.h>
> #include <grub/efi/efi.h>
> #include <grub/i18n.h>
> +#include <grub/env.h>
> 
> GRUB_MOD_LICENSE ("GPLv3+");
> 
> @@ -250,6 +251,7 @@ grub_efi_net_config_real (grub_efi_handle_t hnd, char 
> **device,
>                     &pxe_mode->dhcp_ack,
>                     sizeof (pxe_mode->dhcp_ack),
>                     1, device, path);
> +    grub_env_set ("efi_boot_interface", card->name);
>      return;
>    }
> }
> -- 
> tg: (93daf86..) e/uefi_pxe_vars (depends on: master)
> 
> 
> _______________________________________________
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> 

Thank you very much, Andrey.  This worked.  I did have to add the following 
lines to "grub-core/Makefile.core.am" to get a "eval.mod" generated, but I'm 
sure that it's probably because I missed an important step that would have 
automatically generated it.


if COND_x86_64_efi
platform_PROGRAMS += eval.module
MODULE_FILES += eval.module$(EXEEXT)
eval_module_SOURCES  = commands/eval.c  ## platform sources
nodist_eval_module_SOURCES  =  ## platform nodist sources
eval_module_LDADD  =
eval_module_CFLAGS  = $(AM_CFLAGS) $(CFLAGS_MODULE)
eval_module_LDFLAGS  = $(AM_LDFLAGS) $(LDFLAGS_MODULE)
eval_module_CPPFLAGS  = $(AM_CPPFLAGS) $(CPPFLAGS_MODULE)
eval_module_CCASFLAGS  = $(AM_CCASFLAGS) $(CCASFLAGS_MODULE)
EXTRA_DIST +=
BUILT_SOURCES += $(nodist_eval_module_SOURCES)
CLEANFILES += $(nodist_eval_module_SOURCES)
MOD_FILES += eval.mod
MARKER_FILES += eval.marker
CLEANFILES += eval.marker

eval.marker: $(eval_module_SOURCES) $(nodist_eval_module_SOURCES)
        $(TARGET_CPP) -DGRUB_LST_GENERATOR $(CPPFLAGS_MARKER) $(DEFS) 
$(DEFAULT_INCLUDES) $(INCLUDES) $(eval_module_CPPFLAGS) $(CPPFLAGS) $^ > 
address@hidden || (rm -f $@; exit 1)
        grep 'MARKER' address@hidden > $@; rm -f address@hidden
endif

Anyway, thank you once again.

Rigoberto