LithosAnanake/kernel/src/capsule/zuse_eligibility.c

/*
  StarForth — Steady-State Virtual Machine Runtime

  Copyright (c) 2023–2025 Robert A. James
  All rights reserved.

  Licensed under the StarForth License, Version 1.0
*/

#ifndef __STARKERNEL__
#error "zuse_eligibility.c is kernel-only"
#endif

#include "starkernel/zuse_eligibility.h"
#include "starkernel/zuse_eligibility_list.h"
#include "block_subsystem.h" /* compute_crc64(), blk_meta_zone_read/write */
#include <string.h>
#include <stddef.h>

/* Read and validate one devblock of the chain. Mirrors
 * capsule_zuse_boot.c's genesis_marker_read() convention exactly: magic
 * mismatch, version mismatch, and CRC mismatch are all merged into a
 * single -1 ("treat as absent/corrupt, not present") -- the fence region
 * is never zeroed at format time (block_subsystem.c's blk_commit_format()
 * only zeroes BAM/reloc), so blank foreign bytes and genuine corruption
 * are indistinguishable and must be handled identically here. */
static int list_devblock_read(uint32_t devblock_from_top, zuse_eligibility_devblock_t *out) {
    if (blk_meta_zone_read(devblock_from_top, (uint8_t *)out) != 0) return -1;
    if (out->magic != ZUSE_ELIGIBILITY_LIST_MAGIC) return -1;
    if (out->version != ZUSE_ELIGIBILITY_LIST_VERSION) return -1;
    if (out->count > ZUSE_ELIGIBILITY_ENTRIES_PER_DEVBLOCK) return -1;
    uint64_t want_crc = compute_crc64((const uint8_t *)out,
                                       offsetof(zuse_eligibility_devblock_t, crc));
    if (want_crc != out->crc) return -1;
    return 0;
}

static int list_devblock_write(uint32_t devblock_from_top, zuse_eligibility_devblock_t *blk) {
    blk->crc = compute_crc64((const uint8_t *)blk, offsetof(zuse_eligibility_devblock_t, crc));
    return blk_meta_zone_write(devblock_from_top, (const uint8_t *)blk) == 0 ? 0 : -1;
}

int zuse_eligibility_is_member(const uint8_t pubkey[32]) {
    uint32_t devblock = ZUSE_ELIGIBILITY_LIST_HEAD_DEVBLOCK;
    zuse_eligibility_devblock_t blk;

    for (;;) {
        if (list_devblock_read(devblock, &blk) != 0) return 0; /* fail-closed */
        for (uint32_t i = 0; i < blk.count; i++) {
            if (memcmp(blk.entries[i], pubkey, 32) == 0) return 1;
        }
        if (blk.next_devblock_from_top == ZUSE_ELIGIBILITY_LIST_NO_NEXT) return 0;
        devblock = blk.next_devblock_from_top;
    }
}

int zuse_eligibility_add(const uint8_t pubkey[32]) {
    uint32_t devblock = ZUSE_ELIGIBILITY_LIST_HEAD_DEVBLOCK;
    zuse_eligibility_devblock_t blk;

    if (list_devblock_read(devblock, &blk) != 0) {
        /* List doesn't exist yet (blank fence, or this is genuinely the
         * first entry ever added) -- create the head devblock fresh. */
        memset(&blk, 0, sizeof(blk));
        blk.magic  = ZUSE_ELIGIBILITY_LIST_MAGIC;
        blk.version = ZUSE_ELIGIBILITY_LIST_VERSION;
        blk.count = 1;
        blk.next_devblock_from_top = ZUSE_ELIGIBILITY_LIST_NO_NEXT;
        memcpy(blk.entries[0], pubkey, 32);
        return list_devblock_write(devblock, &blk);
    }

    /* Walk the existing chain: bail out early (idempotent success) if
     * already present, otherwise track the tail devblock to append to. */
    for (;;) {
        for (uint32_t i = 0; i < blk.count; i++) {
            if (memcmp(blk.entries[i], pubkey, 32) == 0) return 0; /* already eligible */
        }
        if (blk.next_devblock_from_top == ZUSE_ELIGIBILITY_LIST_NO_NEXT) break;
        devblock = blk.next_devblock_from_top;
        if (list_devblock_read(devblock, &blk) != 0) return -1; /* corrupt mid-chain */
    }

    if (blk.count < ZUSE_ELIGIBILITY_ENTRIES_PER_DEVBLOCK) {
        memcpy(blk.entries[blk.count], pubkey, 32);
        blk.count++;
        return list_devblock_write(devblock, &blk);
    }

    /* Tail devblock is full -- chain a fresh one drawn from the
     * already-reserved fence budget, one devblock_from_top past the
     * current tail (blk_meta_zone_write() itself refuses any offset at
     * or beyond the on-disk meta_fence_blocks reservation, so an
     * exhausted budget surfaces here as an ordinary write failure). */
    uint32_t new_devblock = devblock + 1;
    zuse_eligibility_devblock_t new_blk;
    memset(&new_blk, 0, sizeof(new_blk));
    new_blk.magic   = ZUSE_ELIGIBILITY_LIST_MAGIC;
    new_blk.version = ZUSE_ELIGIBILITY_LIST_VERSION;
    new_blk.count   = 1;
    new_blk.next_devblock_from_top = ZUSE_ELIGIBILITY_LIST_NO_NEXT;
    memcpy(new_blk.entries[0], pubkey, 32);
    if (list_devblock_write(new_devblock, &new_blk) != 0) return -1;

    blk.next_devblock_from_top = new_devblock;
    return list_devblock_write(devblock, &blk);
}