source: MondoRescue/branches/3.3/mindi-busybox/util-linux/uevent.c@ 3625

/*
 * Copyright 2015 Denys Vlasenko
 *
 * Licensed under GPLv2, see file LICENSE in this source tree.
 */

//config:config UEVENT
//config:   bool "uevent"
//config:   default y
//config:   select PLATFORM_LINUX
//config:   help
//config:     uevent is a netlink listener for kernel uevent notifications
//config:     sent via netlink. It is usually used for dynamic device creation.

//applet:IF_UEVENT(APPLET(uevent, BB_DIR_SBIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_UEVENT) += uevent.o

//usage:#define uevent_trivial_usage
//usage:       "[PROG [ARGS]]"
//usage:#define uevent_full_usage "\n\n"
//usage:       "uevent runs PROG for every netlink notification."
//usage:   "\n""PROG's environment contains data passed from the kernel."
//usage:   "\n""Typical usage (daemon for dynamic device node creation):"
//usage:   "\n""    # uevent mdev & mdev -s"

#include "libbb.h"
#include "common_bufsiz.h"
#include <linux/netlink.h>

#define BUFFER_SIZE 16*1024

#define env ((char **)bb_common_bufsiz1)
#define INIT_G() do { setup_common_bufsiz(); } while (0)
enum {
    MAX_ENV = COMMON_BUFSIZE / sizeof(env[0]) - 1,
};

#ifndef SO_RCVBUFFORCE
#define SO_RCVBUFFORCE 33
#endif
enum { RCVBUF = 2 * 1024 * 1024 };

int uevent_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int uevent_main(int argc UNUSED_PARAM, char **argv)
{
    struct sockaddr_nl sa;
    int fd;

    INIT_G();

    argv++;

    // Subscribe for UEVENT kernel messages
    sa.nl_family = AF_NETLINK;
    sa.nl_pad = 0;
    sa.nl_pid = getpid();
    sa.nl_groups = 1 << 0;
    fd = xsocket(AF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
    xbind(fd, (struct sockaddr *) &sa, sizeof(sa));
    close_on_exec_on(fd);

    // Without a sufficiently big RCVBUF, a ton of simultaneous events
    // can trigger ENOBUFS on read, which is unrecoverable.
    // Reproducer:
    //  uevent mdev &
    //  find /sys -name uevent -exec sh -c 'echo add >"{}"' ';'
    //
    // SO_RCVBUFFORCE (root only) can go above net.core.rmem_max sysctl
    setsockopt_SOL_SOCKET_int(fd, SO_RCVBUF,      RCVBUF);
    setsockopt_SOL_SOCKET_int(fd, SO_RCVBUFFORCE, RCVBUF);
    if (0) {
        int z;
        socklen_t zl = sizeof(z);
        getsockopt(fd, SOL_SOCKET, SO_RCVBUF, &z, &zl);
        bb_error_msg("SO_RCVBUF:%d", z);
    }

    for (;;) {
        char *netbuf;
        char *s, *end;
        ssize_t len;
        int idx;

        // In many cases, a system sits for *days* waiting
        // for a new uevent notification to come in.
        // We use a fresh mmap so that buffer is not allocated
        // until kernel actually starts filling it.
        netbuf = mmap(NULL, BUFFER_SIZE,
                    PROT_READ | PROT_WRITE,
                    MAP_PRIVATE | MAP_ANON,
                    /* ignored: */ -1, 0);
        if (netbuf == MAP_FAILED)
            bb_perror_msg_and_die("mmap");

        // Here we block, possibly for a very long time
        len = safe_read(fd, netbuf, BUFFER_SIZE - 1);
        if (len < 0)
            bb_perror_msg_and_die("read");
        end = netbuf + len;
        *end = '\0';

        // Each netlink message starts with "ACTION@/path"
        // (which we currently ignore),
        // followed by environment variables.
        if (!argv[0])
            putchar('\n');
        idx = 0;
        s = netbuf;
        while (s < end) {
            if (!argv[0])
                puts(s);
            if (strchr(s, '=') && idx < MAX_ENV)
                env[idx++] = s;
            s += strlen(s) + 1;
        }
        env[idx] = NULL;

        idx = 0;
        while (env[idx])
            putenv(env[idx++]);
        if (argv[0])
            spawn_and_wait(argv);
        idx = 0;
        while (env[idx])
            bb_unsetenv(env[idx++]);
        munmap(netbuf, BUFFER_SIZE);
    }

    return 0; // not reached
}