122 lines
3.5 KiB
C
122 lines
3.5 KiB
C
/*
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* Copyright (C) 2001-2003 Hewlett-Packard Co.
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* Contributed by Stephane Eranian <eranian@hpl.hp.com>
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* Contributed by Fenghua Yu <fenghua.yu@intel.com>
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* Contributed by Bibo Mao <bibo.mao@intel.com>
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* Contributed by Chandramouli Narayanan<mouli@linux.intel.com>
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*
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* This file is part of the ELILO, the EFI Linux boot loader.
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*
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* ELILO is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* ELILO is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with ELILO; see the file COPYING. If not, write to the Free
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* Software Foundation, 59 Temple Place - Suite 330, Boston, MA
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* 02111-1307, USA.
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*
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* Please check out the elilo.txt for complete documentation on how
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* to use this program.
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*/
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#include <efi.h>
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#include <efilib.h>
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#include "elilo.h"
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#define ELILO_ALTK_VAR L"EliloAlt"
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/*
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* we use a NULL GUID for now because it is more convenient
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*/
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static EFI_GUID altk_guid={0,};
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/*
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* Check for the existence of an EFI variable named EliloAlt.
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* It contains the name of an alternate kernel (and possible options)
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* to boot ONLY once.
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* The variable is then deleted. This ensures that next reboot won't
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* pick it up.
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*
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* The content of the variable is assumed to be Unicode string. It is
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* preferrably NULL terminated but the code can deal with this as well.
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*
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* The size of the buffer MUST be expressed in bytes (not CHAR16).
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*
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* Return:
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* - 0 if successful
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* - -1 in case nothing happened (no variable found)
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* Please note that no fatal error is reported by this function
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*/
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INTN
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alternate_kernel(CHAR16 *buffer, UINTN size)
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{
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EFI_STATUS status;
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INTN ret = -1;
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/*
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* size of the buffer is expressed in bytes
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*
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* we reserve one Unicode for CHAR_NULL (forced), so
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* the buffer must be at least 2 more bytes to accomodate one Unicode
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*/
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if (size < 4) return -1;
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/*
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* reserve for CHAR_NULL
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*/
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size-=2;
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/*
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* Look if the variable exists.
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* We may fail because:
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* - the variable does not exist
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* - our buffer size is too small.
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*/
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status = uefi_call_wrapper(RT->GetVariable, 5, ELILO_ALTK_VAR, &altk_guid, NULL, &size, buffer);
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if (EFI_ERROR(status)) {
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DBG_PRT((L"cannot access variable %s: %r", ELILO_ALTK_VAR, status));
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/* if buffer is too small, erase variable because it's unuseable */
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if (status == EFI_BUFFER_TOO_SMALL) goto delete_var;
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return -1;
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}
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/*
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* sanity check
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*
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* verify that size (expressed in bytes) is multiple of 2. If
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* not then it can't possibly be representing a UNICODE string
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* (2bytes/character).
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*
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* We also consider empty as useless (2nd test).
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*/
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if (size & 0x1) {
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Print(L"invalid content for %s variable, erasing variable\n", ELILO_ALTK_VAR);
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goto delete_var;
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}
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/* We also consider empty as useless (2nd test) */
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if (size == 2) goto delete_var;
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buffer[size] = CHAR_NULL;
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VERB_PRT(2, Print(L"found alternate variable %s : %s\n", ELILO_ALTK_VAR, buffer));
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ret = 0;
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delete_var:
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status = uefi_call_wrapper(RT->SetVariable, 5, ELILO_ALTK_VAR, &altk_guid, 0, 0, NULL);
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if (EFI_ERROR(status)) {
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ERR_PRT((L"cannot erase variable %s", ELILO_ALTK_VAR));
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}
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return ret;
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}
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