LXR busybox/util-linux/uevent.c

   1/*
   2 * Copyright 2015 Denys Vlasenko
   3 *
   4 * Licensed under GPLv2, see file LICENSE in this source tree.
   5 */
   6//config:config UEVENT
   7//config:       bool "uevent"
   8//config:       default y
   9//config:       select PLATFORM_LINUX
  10//config:       help
  11//config:         uevent is a netlink listener for kernel uevent notifications
  12//config:         sent via netlink. It is usually used for dynamic device creation.
  13
  14//applet:IF_UEVENT(APPLET(uevent, BB_DIR_SBIN, BB_SUID_DROP))
  15
  16//kbuild:lib-$(CONFIG_UEVENT) += uevent.o
  17
  18//usage:#define uevent_trivial_usage
  19//usage:       "[PROG [ARGS]]"
  20//usage:#define uevent_full_usage "\n\n"
  21//usage:       "uevent runs PROG for every netlink notification."
  22//usage:   "\n""PROG's environment contains data passed from the kernel."
  23//usage:   "\n""Typical usage (daemon for dynamic device node creation):"
  24//usage:   "\n""        # uevent mdev & mdev -s"
  25
  26#include "libbb.h"
  27#include "common_bufsiz.h"
  28#include <linux/netlink.h>
  29
  30#define BUFFER_SIZE 16*1024
  31
  32#define env ((char **)bb_common_bufsiz1)
  33#define INIT_G() do { setup_common_bufsiz(); } while (0)
  34enum {
  35        MAX_ENV = COMMON_BUFSIZE / sizeof(env[0]) - 1,
  36};
  37
  38#ifndef SO_RCVBUFFORCE
  39#define SO_RCVBUFFORCE 33
  40#endif
  41enum { RCVBUF = 2 * 1024 * 1024 };
  42
  43int uevent_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  44int uevent_main(int argc UNUSED_PARAM, char **argv)
  45{
  46        struct sockaddr_nl sa;
  47        int fd;
  48
  49        INIT_G();
  50
  51        argv++;
  52
  53        // Subscribe for UEVENT kernel messages
  54        sa.nl_family = AF_NETLINK;
  55        sa.nl_pad = 0;
  56        sa.nl_pid = getpid();
  57        sa.nl_groups = 1 << 0;
  58        fd = xsocket(AF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
  59        xbind(fd, (struct sockaddr *) &sa, sizeof(sa));
  60        close_on_exec_on(fd);
  61
  62        // Without a sufficiently big RCVBUF, a ton of simultaneous events
  63        // can trigger ENOBUFS on read, which is unrecoverable.
  64        // Reproducer:
  65        //      uevent mdev &
  66        //      find /sys -name uevent -exec sh -c 'echo add >"{}"' ';'
  67        //
  68        // SO_RCVBUFFORCE (root only) can go above net.core.rmem_max sysctl
  69        setsockopt_SOL_SOCKET_int(fd, SO_RCVBUF,      RCVBUF);
  70        setsockopt_SOL_SOCKET_int(fd, SO_RCVBUFFORCE, RCVBUF);
  71        if (0) {
  72                int z;
  73                socklen_t zl = sizeof(z);
  74                getsockopt(fd, SOL_SOCKET, SO_RCVBUF, &z, &zl);
  75                bb_error_msg("SO_RCVBUF:%d", z);
  76        }
  77
  78        for (;;) {
  79                char *netbuf;
  80                char *s, *end;
  81                ssize_t len;
  82                int idx;
  83
  84                // In many cases, a system sits for *days* waiting
  85                // for a new uevent notification to come in.
  86                // We use a fresh mmap so that buffer is not allocated
  87                // until kernel actually starts filling it.
  88                netbuf = mmap(NULL, BUFFER_SIZE,
  89                                        PROT_READ | PROT_WRITE,
  90                                        MAP_PRIVATE | MAP_ANON,
  91                                        /* ignored: */ -1, 0);
  92                if (netbuf == MAP_FAILED)
  93                        bb_perror_msg_and_die("mmap");
  94
  95                // Here we block, possibly for a very long time
  96                len = safe_read(fd, netbuf, BUFFER_SIZE - 1);
  97                if (len < 0)
  98                        bb_perror_msg_and_die("read");
  99                end = netbuf + len;
 100                *end = '\0';
 101
 102                // Each netlink message starts with "ACTION@/path"
 103                // (which we currently ignore),
 104                // followed by environment variables.
 105                if (!argv[0])
 106                        putchar('\n');
 107                idx = 0;
 108                s = netbuf;
 109                while (s < end) {
 110                        if (!argv[0])
 111                                puts(s);
 112                        if (strchr(s, '=') && idx < MAX_ENV)
 113                                env[idx++] = s;
 114                        s += strlen(s) + 1;
 115                }
 116                env[idx] = NULL;
 117
 118                idx = 0;
 119                while (env[idx])
 120                        putenv(env[idx++]);
 121                if (argv[0])
 122                        spawn_and_wait(argv);
 123                idx = 0;
 124                while (env[idx])
 125                        bb_unsetenv(env[idx++]);
 126                munmap(netbuf, BUFFER_SIZE);
 127        }
 128
 129        return 0; // not reached
 130}
 131