isfshax/stage2/isfs/isfshax.c

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2021-05-26 01:53:11 +02:00
/*
* isfshax.c
*
* Copyright (C) 2021 rw-r-r-0644 <rwrr0644@gmail.com>
*
* This code is licensed to you under the terms of the GNU GPL, version 2;
* see file COPYING or http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt
*
*
* isfshax is installed to 4 superblock slots for redundancy
* against ecc errors and nand blocks wear out.
*
* when a boot1 superblock recommit attempt (due to ecc errors)
* is detected, the superblock will be rewritten to the next
* isfshax slot after correcting ecc errors.
*
* the generation number is incremented after each correction;
* once the maximum allowed genertion number is reached, all
* isfshax superblocks are rewritten with a lower generation number.
*
* if one of the blocks becomes bad during the rewrite,
* the range of used generations numbers is incremented to ensure
* the old superblock will not be used:
* 0 BAD BLOCKS -> generation no. 0xfffffaff-0xfffffbff
* ...
* 3 BAD BLOCKS -> generation no. 0xfffffdff-0xfffffeff
*
* bad block information is stored along with other informations in a
* separate isfshax info structure inside of the superblock, since all
* isfshax slots are already marked as bad to guard against IOSU intervention
* inside of the normal ISFS cluster allocation table.
*/
#include "types.h"
#include "isfs/isfs.h"
#include "isfs/super.h"
#include "isfs/volume.h"
#include "isfs/isfshax.h"
#include "malloc.h"
/* boot1 superblock loading address.
* this can be used to read the current generation
* and the list of isfshax superblock slots, but it
* can't be rewritten directly to nand as it has been
* modified by the stage1 payload. */
static const isfshax_super *
boot1_superblock = (const isfshax_super *)(0x01f80000);
static isfshax_super
superblock;
int isfshax_refresh()
{
isfs_ctx *slc = isfs_get_volume(ISFSVOL_SLC);
u32 curindex, offs, count = 1, written = 0;
u32 generation;
/* detect if the superblock contains ecc errors and boot1
* attempted to recommit the superblock */
if (boot1_superblock->generation == boot1_superblock->isfshax.generation)
return 0;
/* load the newest valid isfshax superblock slot */
curindex = boot1_superblock->isfshax.index;
for (offs = 0; offs < ISFSHAX_REDUNDANCY; offs++) {
u32 index = (curindex + offs) & (ISFSHAX_REDUNDANCY - 1);
u32 slot = boot1_superblock->isfshax.slots[index] & ~ISFSHAX_BAD_SLOT;
if (isfs_read_super(slc, &superblock, slot) >= 0) {
curindex = index;
break;
}
}
if (offs == ISFSHAX_REDUNDANCY)
return -2;
/* if the last valid generation is reached, rewrite/erase all
* isfshax superblocks with a lower generation number */
generation = superblock.generation + 1;
if (generation >= (superblock.isfshax.generationbase + ISFSHAX_GENERATION_RANGE)) {
generation = superblock.isfshax.generationbase;
count = ISFSHAX_REDUNDANCY;
}
for (offs = 1; (offs <= ISFSHAX_REDUNDANCY) && (written < count); offs++) {
u32 index = (curindex + offs) & (ISFSHAX_REDUNDANCY - 1);
u32 slot = superblock.isfshax.slots[index] & ~ISFSHAX_BAD_SLOT;
/* skip slots that became bad after a superblock rewrite */
if (superblock.isfshax.slots[index] & ISFSHAX_BAD_SLOT)
continue;
/* if the slot currently in use is being rewritten, ensure
* at least another slot was already successfully written */
if ((index == curindex) && !written)
continue;
/* update superblock informations */
superblock.isfshax.index = index;
superblock.isfshax.generation = generation;
superblock.generation = generation;
/* rewrite and verify the superblock */
if (isfs_write_super(slc, &superblock, slot) >= 0)
{
generation++;
written++;
continue;
}
/* block became bad during write operation, mark
* the block as bad and go to next generation range */
superblock.isfshax.slots[index] |= ISFSHAX_BAD_SLOT;
superblock.isfshax.generationbase += ISFSHAX_GENERATION_RANGE;
generation = superblock.isfshax.generationbase;
/* the current superblock became bad. ensure the other
* isfshax superblock are updated with the new generation range
* and bad slot information. */
if (index == curindex)
{
offs = 1;
written = 0;
}
}
/* all isfshax superblocks became bad, or the nand writing code stopped
* working correctly. either way the user should probably be informed. */
if (!written)
return -3;
return 0;
}