Define the Bootloader Control A/B structure

 * commandline parameter. This is used by fs_mgr to mount /system and

 * other partitions with the slotselect flag set in fstab. A/B

 * implementations are free to use all 32 bytes and may store private

 * data past the first NUL-byte in this field.

 * data past the first NUL-byte in this field. It is encouraged, but

 * not mandatory, to use 'struct bootloader_control' described below.

 */

struct bootloader_message {

    char command[32];

    char reserved[192];

};

#define BOOT_CTRL_MAGIC   0x42414342 /* Bootloader Control AB */

#define BOOT_CTRL_VERSION 1

struct slot_metadata {

    // Slot priority with 15 meaning highest priority, 1 lowest

    // priority and 0 the slot is unbootable.

    uint8_t priority : 4;

    // Number of times left attempting to boot this slot.

    uint8_t tries_remaining : 3;

    // 1 if this slot has booted successfully, 0 otherwise.

    uint8_t successful_boot : 1;

    // Reserved for further use.

    uint8_t reserved;

} __attribute__((packed));

/* Bootloader Control AB

 *

 * This struct can be used to manage A/B metadata. It is designed to

 * be put in the 'slot_suffix' field of the 'bootloader_message'

 * structure described above. It is encouraged to use the

 * 'bootloader_control' structure to store the A/B metadata, but not

 * mandatory.

 */

struct bootloader_control {

    // NUL terminated active slot suffix.

    char slot_suffix[4];

    // Bootloader Control AB magic number (see BOOT_CTRL_MAGIC).

    uint32_t magic;

    // Version of struct being used (see BOOT_CTRL_VERSION).

    uint8_t version;

    // Number of slots being managed.

    uint8_t nb_slot : 3;

    // Number of times left attempting to boot recovery.

    uint8_t recovery_tries_remaining : 3;

    // Ensure 4-bytes alignment for slot_info field.

    uint8_t reserved0[2];

    // Per-slot information.  Up to 4 slots.

    struct slot_metadata slot_info[4];

    // Reserved for further use.

    uint8_t reserved1[8];

    // CRC32 of all 28 bytes preceding this field (little endian

    // format).

    uint32_t crc32_le;

} __attribute__((packed));

#if (__STDC_VERSION__ >= 201112L)

_Static_assert(sizeof(struct bootloader_control) ==

               sizeof(((struct bootloader_message *)0)->slot_suffix),

               "struct bootloader_control has wrong size");

#endif

/* Read and write the bootloader command from the "misc" partition.

 * These return zero on success.

 */