1 | /*
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2 | * Copyright 2015 Denys Vlasenko
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3 | *
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4 | * Licensed under GPLv2, see file LICENSE in this source tree.
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5 | */
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6 |
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7 | //config:config UEVENT
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8 | //config: bool "uevent"
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9 | //config: default y
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10 | //config: select PLATFORM_LINUX
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11 | //config: help
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12 | //config: uevent is a netlink listener for kernel uevent notifications
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13 | //config: sent via netlink. It is usually used for dynamic device creation.
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14 |
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15 | //applet:IF_UEVENT(APPLET(uevent, BB_DIR_SBIN, BB_SUID_DROP))
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16 |
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17 | //kbuild:lib-$(CONFIG_UEVENT) += uevent.o
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18 |
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19 | //usage:#define uevent_trivial_usage
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20 | //usage: "[PROG [ARGS]]"
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21 | //usage:#define uevent_full_usage "\n\n"
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22 | //usage: "uevent runs PROG for every netlink notification."
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23 | //usage: "\n""PROG's environment contains data passed from the kernel."
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24 | //usage: "\n""Typical usage (daemon for dynamic device node creation):"
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25 | //usage: "\n"" # uevent mdev & mdev -s"
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26 |
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27 | #include "libbb.h"
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28 | #include "common_bufsiz.h"
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29 | // BCO for RHEL4
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30 | #include <linux/types.h>
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31 | #ifndef NETLINK_KOBJECT_UEVENT
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32 | #define NETLINK_KOBJECT_UEVENT 15 /* Kernel messages to userspace */
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33 | #endif
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34 | // BCO
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35 | #include <linux/netlink.h>
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36 |
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37 | #define BUFFER_SIZE 16*1024
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38 |
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39 | #define env ((char **)bb_common_bufsiz1)
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40 | #define INIT_G() do { setup_common_bufsiz(); } while (0)
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41 | enum {
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42 | MAX_ENV = COMMON_BUFSIZE / sizeof(env[0]) - 1,
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43 | };
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44 |
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45 | #ifndef SO_RCVBUFFORCE
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46 | #define SO_RCVBUFFORCE 33
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47 | #endif
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48 | enum { RCVBUF = 2 * 1024 * 1024 };
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49 |
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50 | int uevent_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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51 | int uevent_main(int argc UNUSED_PARAM, char **argv)
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52 | {
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53 | struct sockaddr_nl sa;
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54 | int fd;
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55 |
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56 | INIT_G();
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57 |
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58 | argv++;
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59 |
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60 | // Subscribe for UEVENT kernel messages
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61 | sa.nl_family = AF_NETLINK;
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62 | sa.nl_pad = 0;
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63 | sa.nl_pid = getpid();
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64 | sa.nl_groups = 1 << 0;
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65 | fd = xsocket(AF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
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66 | xbind(fd, (struct sockaddr *) &sa, sizeof(sa));
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67 | close_on_exec_on(fd);
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68 |
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69 | // Without a sufficiently big RCVBUF, a ton of simultaneous events
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70 | // can trigger ENOBUFS on read, which is unrecoverable.
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71 | // Reproducer:
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72 | // uevent mdev &
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73 | // find /sys -name uevent -exec sh -c 'echo add >"{}"' ';'
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74 | //
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75 | // SO_RCVBUFFORCE (root only) can go above net.core.rmem_max sysctl
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76 | setsockopt_SOL_SOCKET_int(fd, SO_RCVBUF, RCVBUF);
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77 | setsockopt_SOL_SOCKET_int(fd, SO_RCVBUFFORCE, RCVBUF);
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78 | if (0) {
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79 | int z;
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80 | socklen_t zl = sizeof(z);
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81 | getsockopt(fd, SOL_SOCKET, SO_RCVBUF, &z, &zl);
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82 | bb_error_msg("SO_RCVBUF:%d", z);
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83 | }
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84 |
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85 | for (;;) {
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86 | char *netbuf;
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87 | char *s, *end;
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88 | ssize_t len;
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89 | int idx;
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90 |
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91 | // In many cases, a system sits for *days* waiting
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92 | // for a new uevent notification to come in.
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93 | // We use a fresh mmap so that buffer is not allocated
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94 | // until kernel actually starts filling it.
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95 | netbuf = mmap(NULL, BUFFER_SIZE,
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96 | PROT_READ | PROT_WRITE,
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97 | MAP_PRIVATE | MAP_ANON,
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98 | /* ignored: */ -1, 0);
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99 | if (netbuf == MAP_FAILED)
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100 | bb_perror_msg_and_die("mmap");
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101 |
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102 | // Here we block, possibly for a very long time
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103 | len = safe_read(fd, netbuf, BUFFER_SIZE - 1);
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104 | if (len < 0)
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105 | bb_perror_msg_and_die("read");
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106 | end = netbuf + len;
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107 | *end = '\0';
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108 |
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109 | // Each netlink message starts with "ACTION@/path"
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110 | // (which we currently ignore),
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111 | // followed by environment variables.
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112 | if (!argv[0])
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113 | putchar('\n');
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114 | idx = 0;
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115 | s = netbuf;
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116 | while (s < end) {
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117 | if (!argv[0])
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118 | puts(s);
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119 | if (strchr(s, '=') && idx < MAX_ENV)
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120 | env[idx++] = s;
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121 | s += strlen(s) + 1;
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122 | }
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123 | env[idx] = NULL;
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124 |
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125 | idx = 0;
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126 | while (env[idx])
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127 | putenv(env[idx++]);
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128 | if (argv[0])
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129 | spawn_and_wait(argv);
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130 | idx = 0;
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131 | while (env[idx])
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132 | bb_unsetenv(env[idx++]);
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133 | munmap(netbuf, BUFFER_SIZE);
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134 | }
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135 |
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136 | return 0; // not reached
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137 | }
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