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/*
* Copyright (C) 2001-2003 Hewlett-Packard Co.
* Contributed by Stephane Eranian <eranian@hpl.hp.com>
* Contributed by Fenghua Yu <fenghua.yu@intel.com>
* Contributed by Bibo Mao <bibo.mao@intel.com>
* Contributed by Chandramouli Narayanan<mouli@linux.intel.com>
*
* This file is part of the ELILO, the EFI Linux boot loader.
*
* ELILO 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 2, or (at your option)
* any later version.
*
* ELILO 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 ELILO; see the file COPYING. If not, write to the Free
* Software Foundation, 59 Temple Place - Suite 330, Boston, MA
* 02111-1307, USA.
*
* Please check out the elilo.txt for complete documentation on how
* to use this program.
*/
#include <efi.h>
#include <efilib.h>
#include "elilo.h"
#define ELILO_ALTK_VAR L"EliloAlt"
/*
* we use a NULL GUID for now because it is more convenient
*/
static EFI_GUID altk_guid={0,};
/*
* Check for the existence of an EFI variable named EliloAlt.
* It contains the name of an alternate kernel (and possible options)
* to boot ONLY once.
* The variable is then deleted. This ensures that next reboot won't
* pick it up.
*
* The content of the variable is assumed to be Unicode string. It is
* preferrably NULL terminated but the code can deal with this as well.
*
* The size of the buffer MUST be expressed in bytes (not CHAR16).
*
* Return:
* - 0 if successful
* - -1 in case nothing happened (no variable found)
* Please note that no fatal error is reported by this function
*/
INTN
alternate_kernel(CHAR16 *buffer, UINTN size)
{
EFI_STATUS status;
INTN ret = -1;
/*
* size of the buffer is expressed in bytes
*
* we reserve one Unicode for CHAR_NULL (forced), so
* the buffer must be at least 2 more bytes to accomodate one Unicode
*/
if (size < 4) return -1;
/*
* reserve for CHAR_NULL
*/
size-=2;
/*
* Look if the variable exists.
* We may fail because:
* - the variable does not exist
* - our buffer size is too small.
*/
status = uefi_call_wrapper(RT->GetVariable, 5, ELILO_ALTK_VAR, &altk_guid, NULL, &size, buffer);
if (EFI_ERROR(status)) {
DBG_PRT((L"cannot access variable %s: %r", ELILO_ALTK_VAR, status));
/* if buffer is too small, erase variable because it's unuseable */
if (status == EFI_BUFFER_TOO_SMALL) goto delete_var;
return -1;
}
/*
* sanity check
*
* verify that size (expressed in bytes) is multiple of 2. If
* not then it can't possibly be representing a UNICODE string
* (2bytes/character).
*
* We also consider empty as useless (2nd test).
*/
if (size & 0x1) {
Print(L"invalid content for %s variable, erasing variable\n", ELILO_ALTK_VAR);
goto delete_var;
}
/* We also consider empty as useless (2nd test) */
if (size == 2) goto delete_var;
buffer[size] = CHAR_NULL;
VERB_PRT(2, Print(L"found alternate variable %s : %s\n", ELILO_ALTK_VAR, buffer));
ret = 0;
delete_var:
status = uefi_call_wrapper(RT->SetVariable, 5, ELILO_ALTK_VAR, &altk_guid, 0, 0, NULL);
if (EFI_ERROR(status)) {
ERR_PRT((L"cannot erase variable %s", ELILO_ALTK_VAR));
}
return ret;
}
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