/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <android_ab.h>
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#include <android_bootloader_message.h>
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#include <common.h>
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#include <malloc.h>
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#include <u-boot/crc.h>
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/** android_boot_control_compute_crc - Compute the CRC-32 of the bootloader
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* control struct. Only the bytes up to the crc32_le field are considered for
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* the CRC-32 calculation.
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*/
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static uint32_t android_boot_control_compute_crc(
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struct android_bootloader_control *abc)
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{
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return crc32(0, (void *)abc, offsetof(typeof(*abc), crc32_le));
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}
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/** android_boot_control_default - Initialize android_bootloader_control to the
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* default value which allows to boot all slots in order from the first one.
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* This value should be used when the bootloader message is corrupted, but not
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* when a valid message indicates that all slots are unbootable.
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*/
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void android_boot_control_default(struct android_bootloader_control *abc)
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{
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int i;
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const struct android_slot_metadata metadata = {
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.priority = 15,
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.tries_remaining = 7,
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.successful_boot = 0,
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.verity_corrupted = 0,
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.reserved = 0
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};
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memcpy(abc->slot_suffix, "a\0\0\0", 4);
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abc->magic = ANDROID_BOOT_CTRL_MAGIC;
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abc->version = ANDROID_BOOT_CTRL_VERSION;
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abc->nb_slot = ANDROID_NUM_SLOTS;
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memset(abc->reserved0, 0, sizeof(abc->reserved0));
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for (i = 0; i < abc->nb_slot; ++i) {
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abc->slot_info[i] = metadata;
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}
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memset(abc->reserved1, 0, sizeof(abc->reserved1));
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abc->crc32_le = android_boot_control_compute_crc(abc);
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}
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/** android_boot_control_create_from_disk
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* Load the boot_control struct from disk into newly allocated memory. This
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* function allocates and returns an integer number of disk blocks, based on the
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* block size of the passed device to help performing a read-modify-write
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* operation on the boot_control struct. The boot_control struct offset (2 KiB)
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* must be a multiple of the device block size, for simplicity.
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* @dev_desc: device where to read the boot_control struct from.
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* @part_info: partition in 'dev_desc' where to read from, normally the "misc"
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* partition should be used.
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*/
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static void *android_boot_control_create_from_disk(
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struct blk_desc *dev_desc,
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const disk_partition_t *part_info)
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{
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ulong abc_offset, abc_blocks;
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void *buf;
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abc_offset = offsetof(struct android_bootloader_message_ab,
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slot_suffix);
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if (abc_offset % part_info->blksz) {
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printf("ANDROID: Boot control block not block aligned.\n");
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return NULL;
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}
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abc_offset /= part_info->blksz;
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abc_blocks = DIV_ROUND_UP(sizeof(struct android_bootloader_control),
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part_info->blksz);
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if (abc_offset + abc_blocks > part_info->size) {
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printf("ANDROID: boot control partition too small. Need at"
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" least %lu blocks but have %lu blocks.\n",
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abc_offset + abc_blocks, part_info->size);
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return NULL;
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}
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buf = malloc(abc_blocks * part_info->blksz);
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if (!buf)
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return NULL;
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if (blk_dread(dev_desc, part_info->start + abc_offset, abc_blocks,
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buf) != abc_blocks) {
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printf("ANDROID: Could not read from boot control partition\n");
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free(buf);
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return NULL;
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}
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debug("ANDROID: Loaded ABC, %lu blocks.\n", abc_blocks);
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return buf;
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}
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/** android_boot_control_store
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* Store the loaded boot_control block back to the same location it was read
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* from with android_boot_control_create_from_misc().
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*
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* @abc_data_block: pointer to the boot_control struct and the extra bytes after
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* it up to the nearest block boundary.
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* @dev_desc: device where we should write the boot_control struct.
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* @part_info: partition on the 'dev_desc' where to write.
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* @return 0 on success and -1 on error.
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*/
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static int android_boot_control_store(void *abc_data_block,
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struct blk_desc *dev_desc,
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const disk_partition_t *part_info)
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{
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ulong abc_offset, abc_blocks;
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abc_offset = offsetof(struct android_bootloader_message_ab,
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slot_suffix) / part_info->blksz;
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abc_blocks = DIV_ROUND_UP(sizeof(struct android_bootloader_control),
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part_info->blksz);
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if (blk_dwrite(dev_desc, part_info->start + abc_offset, abc_blocks,
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abc_data_block) != abc_blocks) {
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printf("ANDROID: Could not write back the misc partition\n");
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return -1;
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}
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return 0;
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}
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/** android_boot_compare_slots - compares two slots returning which slot is
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* should we boot from among the two.
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* @a: The first bootable slot metadata
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* @b: The second bootable slot metadata
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* @return negative if the slot "a" is better, positive of the slot "b" is
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* better or 0 if they are equally good.
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*/
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static int android_ab_compare_slots(const struct android_slot_metadata *a,
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const struct android_slot_metadata *b)
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{
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/* Higher priority is better */
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if (a->priority != b->priority)
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return b->priority - a->priority;
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/* Higher successful_boot value is better, in case of same priority. */
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if (a->successful_boot != b->successful_boot)
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return b->successful_boot - a->successful_boot;
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/* Higher tries_remaining is better to ensure round-robin. */
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if (a->tries_remaining != b->tries_remaining)
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return b->tries_remaining - a->tries_remaining;
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return 0;
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}
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int android_ab_select(struct blk_desc *dev_desc, disk_partition_t *part_info)
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{
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struct android_bootloader_control *abc;
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u32 crc32_le;
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int slot, i;
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bool store_needed = false;
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char slot_suffix[4];
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abc = android_boot_control_create_from_disk(dev_desc, part_info);
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if (!abc) {
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/* This condition represents an actual problem with the code
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* or the board setup, like an invalid partition information.
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* Signal a repair mode and do not try to boot from either
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* slot.
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*/
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return -1;
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}
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crc32_le = android_boot_control_compute_crc(abc);
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if (abc->crc32_le != crc32_le) {
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printf("ANDROID: Invalid CRC-32 (expected %.8x, found %.8x), "
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"re-initializing A/B metadata.\n",
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crc32_le, abc->crc32_le);
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android_boot_control_default(abc);
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store_needed = true;
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}
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if (abc->magic != ANDROID_BOOT_CTRL_MAGIC) {
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printf("ANDROID: Unknown A/B metadata: %.8x\n", abc->magic);
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free(abc);
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return -1;
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}
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if (abc->version > ANDROID_BOOT_CTRL_VERSION) {
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printf("ANDROID: Unsupported A/B metadata version: %.8x\n",
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abc->version);
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free(abc);
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return -1;
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}
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/* At this point a valid boot control metadata is stored in abc,
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* followed by other reserved data in the same block.
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* We select a with the higher priority slot that
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* - is not marked as corrupted and
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* - either has tries_remaining > 0 or successful_boot is true.
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* If the slot selected has a false successful_boot, we also decrement
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* the tries_remaining until it eventually becomes unbootable because
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* tries_remaining reaches 0. This mechanism produces a bootloader
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* induced rollback, typically right after a failed update.
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*/
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/* Safety check: limit the number of slots. */
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if (abc->nb_slot > ARRAY_SIZE(abc->slot_info)) {
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abc->nb_slot = ARRAY_SIZE(abc->slot_info);
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store_needed = true;
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}
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slot = -1;
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for (i = 0; i < abc->nb_slot; ++i) {
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if (abc->slot_info[i].verity_corrupted ||
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!abc->slot_info[i].tries_remaining) {
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debug("ANDROID: unbootable slot %d tries: %d, "
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"corrupt: %d\n",
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i,
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abc->slot_info[i].tries_remaining,
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abc->slot_info[i].verity_corrupted);
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continue;
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}
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debug("ANDROID: bootable slot %d pri: %d, tries: %d, "
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"corrupt: %d, successful: %d\n",
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i,
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abc->slot_info[i].priority,
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abc->slot_info[i].tries_remaining,
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abc->slot_info[i].verity_corrupted,
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abc->slot_info[i].successful_boot);
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if (slot < 0 ||
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android_ab_compare_slots(&abc->slot_info[i],
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&abc->slot_info[slot]) < 0) {
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slot = i;
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}
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}
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if (slot >= 0 && !abc->slot_info[slot].successful_boot) {
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printf("ANDROID: Attempting slot %c, tries remaining %d\n",
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ANDROID_BOOT_SLOT_NAME(slot),
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abc->slot_info[slot].tries_remaining);
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abc->slot_info[slot].tries_remaining--;
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store_needed = true;
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}
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if (slot >= 0) {
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/* Legacy user-space requires this field to be set in the BCB.
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* Newer releases load this the slot suffix from the command
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* line or the device tree.
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*/
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memset(slot_suffix, 0, sizeof(slot_suffix));
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slot_suffix[0] = ANDROID_BOOT_SLOT_NAME(slot);
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if (memcmp(abc->slot_suffix, slot_suffix,
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sizeof(slot_suffix))) {
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memcpy(abc->slot_suffix, slot_suffix,
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sizeof(slot_suffix));
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store_needed = true;
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}
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}
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if (store_needed) {
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abc->crc32_le = android_boot_control_compute_crc(abc);
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android_boot_control_store(abc, dev_desc, part_info);
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}
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free(abc);
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if (slot < 0)
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return -1;
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return slot;
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}
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