使用NVMe云盘多重挂载及Reservation实现应用间的数据共享

#define _GNU_SOURCE
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/pr.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <time.h>
#include <unistd.h>

const char *disk_device = "/dev/data-disk";
uint64_t magic = 0x4745D0C5CD9A2FA4;

void panic(const char *restrict format, ...) {
    va_list args;
    va_start(args, format);
    vfprintf(stderr, format, args);
    va_end(args);
    exit(EXIT_FAILURE);
}

struct lease {
    uint64_t magic;
    struct timespec acquire_time;
    char holder[64];
};

volatile bool shutdown = false;
void on_term(int signum) {
    shutdown = true;
}

struct lease *lease;
const size_t lease_alloc_size = 512;

void acquire_lease(int disk_fd) {
    int ret;

    struct pr_registration pr_reg = {
        .new_key = magic,
        .flags = PR_FL_IGNORE_KEY,
    };
    ret = ioctl(disk_fd, IOC_PR_REGISTER, &pr_reg);
    if (ret != 0)
        panic("failed to register (%d): %s\n", ret, strerror(errno));

    struct pr_preempt pr_pre = {
        .old_key = magic,
        .new_key = magic,
        .type  = PR_WRITE_EXCLUSIVE,
    };
    ret = ioctl(disk_fd, IOC_PR_PREEMPT, &pr_pre);
    if (ret != 0)
        panic("failed to preempt (%d): %s\n", ret, strerror(errno));

    // register again in case we preempted ourselves
    ret = ioctl(disk_fd, IOC_PR_REGISTER, &pr_reg);
    if (ret != 0)
        panic("failed to register (%d): %s\n", ret, strerror(errno));
    fprintf(stderr, "Register as key %lx\n", magic);


    struct pr_reservation pr_rev = {
        .key   = magic,
        .type  = PR_WRITE_EXCLUSIVE,
    };
    ret = ioctl(disk_fd, IOC_PR_RESERVE, &pr_rev);
    if (ret != 0)
        panic("failed to reserve (%d): %s\n", ret, strerror(errno));

    lease->magic = magic;
    gethostname(lease->holder, sizeof(lease->holder));

    while (!shutdown) {
        clock_gettime(CLOCK_MONOTONIC, &lease->acquire_time);
        ret = pwrite(disk_fd, lease, lease_alloc_size, 0);
        if (ret < 0)
            panic("failed to write lease: %s\n", strerror(errno));
        fprintf(stderr, "Refreshed lease\n");
        sleep(5);
    }
}

int timespec_compare(const struct timespec *a, const struct timespec *b) {
    if (a->tv_sec < b->tv_sec)
        return -1;
    if (a->tv_sec > b->tv_sec)
        return 1;
    if (a->tv_nsec < b->tv_nsec)
        return -1;
    if (a->tv_nsec > b->tv_nsec)
        return 1;
    return 0;
}

int main() {
    assert(lease_alloc_size >= sizeof(struct lease));
    lease = aligned_alloc(512, lease_alloc_size);
    if (lease == NULL)
        panic("failed to allocate memory\n");

    // char *reg_key_str = getenv("REG_KEY");
    // if (reg_key_str == NULL)
    //     panic("REG_KEY env not specified");

    // uint64_t reg_key = atoll(reg_key_str) | (magic << 32);
    // fprintf(stderr, "Will register as key %lx", reg_key);


    int disk_fd = open(disk_device, O_RDWR|O_DIRECT);
    if (disk_fd < 0)
        panic("failed to open disk: %s\n", strerror(errno));

    // setup signal handler
    struct sigaction sa = {
        .sa_handler = on_term,
    };
    sigaction(SIGTERM, &sa, NULL);
    sigaction(SIGINT, &sa, NULL);

    struct timespec last_active_local;
    struct timespec last_active_remote;

    int ret = pread(disk_fd, lease, lease_alloc_size, 0);
    if (ret < 0)
        panic("failed to read lease: %s\n", strerror(errno));

    if (lease->magic != magic) {
        // new disk, no lease
        acquire_lease(disk_fd);
    } else {
        // someone else has the lease
        while (!shutdown) {
            struct timespec now;
            clock_gettime(CLOCK_MONOTONIC, &now);
            if (timespec_compare(&lease->acquire_time, &last_active_remote)) {
                fprintf(stderr, "Remote %s refreshed lease\n", lease->holder);
                last_active_remote = lease->acquire_time;
                last_active_local = now;
            } else if (now.tv_sec - last_active_local.tv_sec > 20) {
                // remote is dead
                fprintf(stderr, "Remote is dead, preempting\n");
                acquire_lease(disk_fd);
                break;
            }
            sleep(5);
            int ret = pread(disk_fd, lease, lease_alloc_size, 0);
            if (ret < 0)
                panic("failed to read lease: %s\n", strerror(errno));
        }
    }

    close(disk_fd);
}

#!/bin/bash

set -e

DISK_DEVICE="/dev/data-disk"
MAGIC=0x4745D0C5CD9A2FA4

SHUTDOWN=0
trap "SHUTDOWN=1" SIGINT SIGTERM

function acquire_lease() {
    # racqa:
    # 0: aquire
    # 1: preempt

    # rtype:
    # 1: write exclusive

    nvme resv-register $DISK_DEVICE --iekey --nrkey=$MAGIC
    nvme resv-acquire $DISK_DEVICE --racqa=1 --rtype=1 --prkey=$MAGIC --crkey=$MAGIC
    # register again in case we preempted ourselves
    nvme resv-register $DISK_DEVICE --iekey --nrkey=$MAGIC
    nvme resv-acquire $DISK_DEVICE --racqa=0 --rtype=1 --prkey=$MAGIC --crkey=$MAGIC

    while [[ $SHUTDOWN -eq 0 ]]; do
        echo "$MAGIC $(date +%s) $HOSTNAME" | dd of=$DISK_DEVICE bs=512 count=1 oflag=direct status=none
        echo "Refreshed lease"
        sleep 5
    done
}

LEASE=$(dd if=$DISK_DEVICE bs=512 count=1 iflag=direct status=none)

if [[ $LEASE != $MAGIC* ]]; then
    # new disk, no lease
    acquire_lease
else
    last_active_remote=-1
    last_active_local=-1
    while [[ $SHUTDOWN -eq 0 ]]; do
        now=$(date +%s)
        read -r magic timestamp holder < <(echo $LEASE)
        if [ "$last_active_remote" != "$timestamp" ]; then
            echo "Remote $holder refreshed the lease"
            last_active_remote=$timestamp
            last_active_local=$now
        elif (($now - $last_active_local > 10)); then
            echo "Remote is dead, preempting"
            acquire_lease
            break
        fi
        sleep 5
        LEASE=$(dd if=$DISK_DEVICE bs=512 count=1 iflag=direct status=none)
    done
fi