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/* raid6_recover.c - module to recover from faulty RAID6 arrays. */
/*
* GRUB -- GRand Unified Bootloader
* Copyright (C) 2006,2007,2008,2009 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/disk.h>
#include <grub/mm.h>
#include <grub/err.h>
#include <grub/misc.h>
#include <grub/diskfilter.h>
#include <grub/crypto.h>
GRUB_MOD_LICENSE ("GPLv3+");
/* x**y. */
static grub_uint8_t powx[255 * 2];
/* Such an s that x**s = y */
static unsigned powx_inv[256];
static const grub_uint8_t poly = 0x1d;
static void
grub_raid_block_mulx (unsigned mul, char *buf, grub_size_t size)
{
grub_size_t i;
grub_uint8_t *p;
p = (grub_uint8_t *) buf;
for (i = 0; i < size; i++, p++)
if (*p)
*p = powx[mul + powx_inv[*p]];
}
static void
grub_raid6_init_table (void)
{
unsigned i;
grub_uint8_t cur = 1;
for (i = 0; i < 255; i++)
{
powx[i] = cur;
powx[i + 255] = cur;
powx_inv[cur] = i;
if (cur & 0x80)
cur = (cur << 1) ^ poly;
else
cur <<= 1;
}
}
static unsigned
mod_255 (unsigned x)
{
while (x > 0xff)
x = (x >> 8) + (x & 0xff);
if (x == 0xff)
return 0;
return x;
}
static grub_err_t
raid6_recover_read_node (void *data, int disknr,
grub_uint64_t sector,
void *buf, grub_size_t size)
{
struct grub_diskfilter_segment *array = data;
return grub_diskfilter_read_node (&array->nodes[disknr],
(grub_disk_addr_t)sector,
size >> GRUB_DISK_SECTOR_BITS, buf);
}
grub_err_t
grub_raid6_recover_gen (void *data, grub_uint64_t nstripes, int disknr, int p,
char *buf, grub_uint64_t sector, grub_size_t size,
int layout, raid_recover_read_t read_func)
{
int i, q, pos;
int bad1 = -1, bad2 = -1;
char *pbuf = 0, *qbuf = 0;
pbuf = grub_zalloc (size);
if (!pbuf)
goto quit;
qbuf = grub_zalloc (size);
if (!qbuf)
goto quit;
q = p + 1;
if (q == (int) nstripes)
q = 0;
pos = q + 1;
if (pos == (int) nstripes)
pos = 0;
for (i = 0; i < (int) nstripes - 2; i++)
{
int c;
if (layout & GRUB_RAID_LAYOUT_MUL_FROM_POS)
c = pos;
else
c = i;
if (pos == disknr)
bad1 = c;
else
{
if (!read_func (data, pos, sector, buf, size))
{
grub_crypto_xor (pbuf, pbuf, buf, size);
grub_raid_block_mulx (c, buf, size);
grub_crypto_xor (qbuf, qbuf, buf, size);
}
else
{
/* Too many bad devices */
if (bad2 >= 0)
goto quit;
bad2 = c;
grub_errno = GRUB_ERR_NONE;
}
}
pos++;
if (pos == (int) nstripes)
pos = 0;
}
/* Invalid disknr or p */
if (bad1 < 0)
goto quit;
if (bad2 < 0)
{
/* One bad device */
if (!read_func (data, p, sector, buf, size))
{
grub_crypto_xor (buf, buf, pbuf, size);
goto quit;
}
grub_errno = GRUB_ERR_NONE;
if (read_func (data, q, sector, buf, size))
goto quit;
grub_crypto_xor (buf, buf, qbuf, size);
grub_raid_block_mulx (255 - bad1, buf,
size);
}
else
{
/* Two bad devices */
unsigned c;
if (read_func (data, p, sector, buf, size))
goto quit;
grub_crypto_xor (pbuf, pbuf, buf, size);
if (read_func (data, q, sector, buf, size))
goto quit;
grub_crypto_xor (qbuf, qbuf, buf, size);
c = mod_255((255 ^ bad1)
+ (255 ^ powx_inv[(powx[bad2 + (bad1 ^ 255)] ^ 1)]));
grub_raid_block_mulx (c, qbuf, size);
c = mod_255((unsigned) bad2 + c);
grub_raid_block_mulx (c, pbuf, size);
grub_crypto_xor (pbuf, pbuf, qbuf, size);
grub_memcpy (buf, pbuf, size);
}
quit:
grub_free (pbuf);
grub_free (qbuf);
return grub_errno;
}
static grub_err_t
grub_raid6_recover (struct grub_diskfilter_segment *array, int disknr, int p,
char *buf, grub_disk_addr_t sector, grub_size_t size)
{
return grub_raid6_recover_gen (array, array->node_count, disknr, p, buf,
sector, size << GRUB_DISK_SECTOR_BITS,
array->layout, raid6_recover_read_node);
}
GRUB_MOD_INIT(raid6rec)
{
grub_raid6_init_table ();
grub_raid6_recover_func = grub_raid6_recover;
}
GRUB_MOD_FINI(raid6rec)
{
grub_raid6_recover_func = 0;
}
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