src/lxc/monitor.c

	monitor.c revision 8b79a8fec4127c754509d65faae1fe7f09515365
/*
 * lxc: linux Container library
 *
 * (C) Copyright IBM Corp. 2007, 2008
 *
 * Authors:
 * Daniel Lezcano <daniel.lezcano at free.fr>
 * Dwight Engen <dwight.engen@oracle.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <poll.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <net/if.h>
#include <netinet/in.h>
#include <sys/param.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>

#include "config.h"
#include "af_unix.h"
#include "error.h"
#include "log.h"
#include "lxclock.h"
#include "monitor.h"
#include "state.h"
#include "utils.h"

lxc_log_define(lxc_monitor, lxc);

/* routines used by monitor publishers (containers) */
int lxc_monitor_fifo_name(const char *lxcpath, char *fifo_path, size_t fifo_path_sz,
              int do_mkdirp)
{
    int ret;
    char *rundir;

    rundir = get_rundir();
    if (!rundir)
        return -1;

    if (do_mkdirp) {
        ret = snprintf(fifo_path, fifo_path_sz, "%s/lxc/%s", rundir, lxcpath);
        if (ret < 0 || (size_t)ret >= fifo_path_sz) {
            ERROR("rundir/lxcpath (%s/%s) too long for monitor fifo.", rundir, lxcpath);
            free(rundir);
            return -1;
        }
        ret = mkdir_p(fifo_path, 0755);
        if (ret < 0) {
            ERROR("Unable to create monitor fifo directory %s.", fifo_path);
            free(rundir);
            return ret;
        }
    }
    ret = snprintf(fifo_path, fifo_path_sz, "%s/lxc/%s/monitor-fifo", rundir, lxcpath);
    if (ret < 0 || (size_t)ret >= fifo_path_sz) {
        ERROR("rundir/lxcpath (%s/%s) too long for monitor fifo.", rundir, lxcpath);
        free(rundir);
        return -1;
    }
    free(rundir);
    return 0;
}

static void lxc_monitor_fifo_send(struct lxc_msg *msg, const char *lxcpath)
{
    int fd,ret;
    char fifo_path[PATH_MAX];

    BUILD_BUG_ON(sizeof(*msg) > PIPE_BUF); /* write not guaranteed atomic */

    ret = lxc_monitor_fifo_name(lxcpath, fifo_path, sizeof(fifo_path), 0);
    if (ret < 0)
        return;

    /* Open the fifo nonblock in case the monitor is dead, we don't want the
     * open to wait for a reader since it may never come.
     */
    fd = open(fifo_path, O_WRONLY | O_NONBLOCK);
    if (fd < 0) {
        /* It is normal for this open() to fail with ENXIO when there is
         * no monitor running, so we don't log it.
         */
        if (errno == ENXIO)
            return;

        WARN("Failed to open fifo to send message: %s.", strerror(errno));
        return;
    }

    if (fcntl(fd, F_SETFL, O_WRONLY) < 0) {
        close(fd);
        return;
    }

    ret = write(fd, msg, sizeof(*msg));
    if (ret != sizeof(*msg)) {
        close(fd);
        SYSERROR("Failed to write to monitor fifo \"%s\".", fifo_path);
        return;
    }

    close(fd);
}

void lxc_monitor_send_state(const char *name, lxc_state_t state,
                const char *lxcpath)
{
    struct lxc_msg msg = {.type = lxc_msg_state, .value = state};
    strncpy(msg.name, name, sizeof(msg.name));
    msg.name[sizeof(msg.name) - 1] = 0;

    lxc_monitor_fifo_send(&msg, lxcpath);
}

void lxc_monitor_send_exit_code(const char *name, int exit_code,
                const char *lxcpath)
{
    struct lxc_msg msg = {.type = lxc_msg_exit_code, .value = exit_code};
    strncpy(msg.name, name, sizeof(msg.name));
    msg.name[sizeof(msg.name) - 1] = 0;

    lxc_monitor_fifo_send(&msg, lxcpath);
}

/* routines used by monitor subscribers (lxc-monitor) */
int lxc_monitor_close(int fd)
{
    return close(fd);
}

int lxc_monitor_sock_name(const char *lxcpath, struct sockaddr_un *addr) {
    size_t len;
    int ret;
    char *sockname;
    char *path;
    uint64_t hash;

    /* addr.sun_path is only 108 bytes, so we hash the full name and
     * then append as much of the name as we can fit.
     */
    sockname = &addr->sun_path[1];
    memset(addr, 0, sizeof(*addr));
    addr->sun_family = AF_UNIX;

    len = strlen(lxcpath) + 18;
    path = alloca(len);
    ret = snprintf(path, len, "lxc/%s/monitor-sock", lxcpath);
    if (ret < 0 || (size_t)ret >= len) {
        ERROR("Failed to create path for monitor.");
        return -1;
    }

    len = sizeof(addr->sun_path) - 1;
    hash = fnv_64a_buf(path, ret, FNV1A_64_INIT);
    ret = snprintf(sockname, len, "lxc/%016" PRIx64 "/%s", hash, lxcpath);
    if (ret < 0)
        return -1;

    sockname[sizeof(addr->sun_path)-3] = '\0';
    INFO("Using monitor socket name \"%s\".", sockname);

    return 0;
}

int lxc_monitor_open(const char *lxcpath)
{
    struct sockaddr_un addr;
    int fd;
    size_t retry;
    size_t len;
    int ret = 0, backoff_ms[] = {10, 50, 100};

    if (lxc_monitor_sock_name(lxcpath, &addr) < 0)
        return -1;

    fd = socket(PF_UNIX, SOCK_STREAM, 0);
    if (fd < 0) {
        ERROR("Failed to create socket: %s.", strerror(errno));
        return -1;
    }

    len = strlen(&addr.sun_path[1]) + 1;
    if (len >= sizeof(addr.sun_path) - 1) {
        ret = -1;
        errno = ENAMETOOLONG;
        goto on_error;
    }

    for (retry = 0; retry < sizeof(backoff_ms) / sizeof(backoff_ms[0]); retry++) {
        ret = connect(fd, (struct sockaddr *)&addr, offsetof(struct sockaddr_un, sun_path) + len);
        if (ret == 0 || errno != ECONNREFUSED)
            break;
        ERROR("Failed to connect to monitor socket. Retrying in %d ms.", backoff_ms[retry]);
        usleep(backoff_ms[retry] * 1000);
    }

    if (ret < 0) {
        ERROR("Failed to connect to monitor socket: %s.", strerror(errno));
        goto on_error;
    }

    return fd;

on_error:
    close(fd);
    return ret;
}

int lxc_monitor_read_fdset(struct pollfd *fds, nfds_t nfds, struct lxc_msg *msg,
               int timeout)
{
    long i;
    int ret;

    ret = poll(fds, nfds, timeout * 1000);
    if (ret == -1)
        return -1;
    else if (ret == 0)
        return -2;  // timed out

    /* Only read from the first ready fd, the others will remain ready for
     * when this routine is called again.
     */
    for (i = 0; i < nfds; i++) {
        if (fds[i].revents != 0) {
            fds[i].revents = 0;
            ret = recv(fds[i].fd, msg, sizeof(*msg), 0);
            if (ret <= 0) {
                SYSERROR("Failed to receive message. Did monitord die?: %s.", strerror(errno));
                return -1;
            }
            return ret;
        }
    }

    SYSERROR("No ready fd found.");

    return -1;
}

int lxc_monitor_read_timeout(int fd, struct lxc_msg *msg, int timeout)
{
    struct pollfd fds;

    fds.fd = fd;
    fds.events = POLLIN | POLLPRI;
    fds.revents = 0;

    return lxc_monitor_read_fdset(&fds, 1, msg, timeout);
}

int lxc_monitor_read(int fd, struct lxc_msg *msg)
{
    return lxc_monitor_read_timeout(fd, msg, -1);
}

#define LXC_MONITORD_PATH LIBEXECDIR "/lxc/lxc-monitord"

/* Used to spawn a monitord either on startup of a daemon container, or when
 * lxc-monitor starts.
 */
int lxc_monitord_spawn(const char *lxcpath)
{
    int ret;
    int pipefd[2];
    char pipefd_str[LXC_NUMSTRLEN64];
    pid_t pid1, pid2;

    char *const args[] = {
        LXC_MONITORD_PATH,
        (char *)lxcpath,
        pipefd_str,
        NULL,
    };

    /* double fork to avoid zombies when monitord exits */
    pid1 = fork();
    if (pid1 < 0) {
        SYSERROR("Failed to fork().");
        return -1;
    }

    if (pid1) {
        DEBUG("Going to wait for pid %d.", pid1);
        if (waitpid(pid1, NULL, 0) != pid1)
            return -1;
        DEBUG("Finished waiting on pid %d.", pid1);
        return 0;
    }

    if (pipe(pipefd) < 0) {
        SYSERROR("Failed to create pipe.");
        exit(EXIT_FAILURE);
    }

    pid2 = fork();
    if (pid2 < 0) {
        SYSERROR("Failed to fork().");
        exit(EXIT_FAILURE);
    }

    if (pid2) {
        char c;
        /* Wait for daemon to create socket. */
        close(pipefd[1]);

        /* Sync with child, we're ignoring the return from read
         * because regardless if it works or not, either way we've
         * synced with the child process. the if-empty-statement
         * construct is to quiet the warn-unused-result warning.
         */
        if (read(pipefd[0], &c, 1))
            ;

        close(pipefd[0]);

        exit(EXIT_SUCCESS);
    }

    if (setsid() < 0) {
        SYSERROR("Failed to setsid().");
        exit(EXIT_FAILURE);
    }

    lxc_check_inherited(NULL, true, pipefd[1]);
    if (null_stdfds() < 0) {
        SYSERROR("Failed to dup2() standard file descriptors to /dev/null.");
        exit(EXIT_FAILURE);
    }

    close(pipefd[0]);

    ret = snprintf(pipefd_str, LXC_NUMSTRLEN64, "%d", pipefd[1]);
    if (ret < 0 || ret >= LXC_NUMSTRLEN64) {
        ERROR("Failed to create pid argument to pass to monitord.");
        exit(EXIT_FAILURE);
    }

    DEBUG("Using pipe file descriptor %d for monitord.", pipefd[1]);

    execvp(args[0], args);
    ERROR("Failed to exec lxc-monitord.");

    exit(EXIT_FAILURE);
}