2 * Copyright 2015 Denys Vlasenko
4 * Licensed under GPLv2, see file LICENSE in this source tree.
8 //config: bool "uevent"
10 //config: select PLATFORM_LINUX
12 //config: uevent is a netlink listener for kernel uevent notifications
13 //config: sent via netlink. It is usually used for dynamic device creation.
15 //applet:IF_UEVENT(APPLET(uevent, BB_DIR_SBIN, BB_SUID_DROP))
17 //kbuild:lib-$(CONFIG_UEVENT) += uevent.o
19 //usage:#define uevent_trivial_usage
20 //usage: "[PROG [ARGS]]"
21 //usage:#define uevent_full_usage "\n\n"
22 //usage: "uevent runs PROG for every netlink notification."
23 //usage: "\n""PROG's environment contains data passed from the kernel."
24 //usage: "\n""Typical usage (daemon for dynamic device node creation):"
25 //usage: "\n"" # uevent mdev & mdev -s"
28 #include "common_bufsiz.h"
29 #include <linux/netlink.h>
31 #define BUFFER_SIZE 16*1024
33 #define env ((char **)bb_common_bufsiz1)
35 MAX_ENV = COMMON_BUFSIZE / sizeof(env[0]) - 1,
38 #ifndef SO_RCVBUFFORCE
39 #define SO_RCVBUFFORCE 33
41 enum { RCVBUF = 2 * 1024 * 1024 };
43 int uevent_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
44 int uevent_main(int argc UNUSED_PARAM, char **argv)
46 struct sockaddr_nl sa;
51 // Subscribe for UEVENT kernel messages
52 sa.nl_family = AF_NETLINK;
55 sa.nl_groups = 1 << 0;
56 fd = xsocket(AF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
57 xbind(fd, (struct sockaddr *) &sa, sizeof(sa));
60 // Without a sufficiently big RCVBUF, a ton of simultaneous events
61 // can trigger ENOBUFS on read, which is unrecoverable.
64 // find /sys -name uevent -exec sh -c 'echo add >"{}"' ';'
66 // SO_RCVBUFFORCE (root only) can go above net.core.rmem_max sysctl
67 setsockopt_SOL_SOCKET_int(fd, SO_RCVBUF, RCVBUF);
68 setsockopt_SOL_SOCKET_int(fd, SO_RCVBUFFORCE, RCVBUF);
71 socklen_t zl = sizeof(z);
72 getsockopt(fd, SOL_SOCKET, SO_RCVBUF, &z, &zl);
73 bb_error_msg("SO_RCVBUF:%d", z);
82 // In many cases, a system sits for *days* waiting
83 // for a new uevent notification to come in.
84 // We use a fresh mmap so that buffer is not allocated
85 // until kernel actually starts filling it.
86 netbuf = mmap(NULL, BUFFER_SIZE,
87 PROT_READ | PROT_WRITE,
88 MAP_PRIVATE | MAP_ANON,
89 /* ignored: */ -1, 0);
90 if (netbuf == MAP_FAILED)
91 bb_perror_msg_and_die("mmap");
93 // Here we block, possibly for a very long time
94 len = safe_read(fd, netbuf, BUFFER_SIZE - 1);
96 bb_perror_msg_and_die("read");
100 // Each netlink message starts with "ACTION@/path"
101 // (which we currently ignore),
102 // followed by environment variables.
110 if (strchr(s, '=') && idx < MAX_ENV)
120 spawn_and_wait(argv);
123 bb_unsetenv(env[idx++]);
124 munmap(netbuf, BUFFER_SIZE);
127 return 0; // not reached