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)
34 #define INIT_G() do { setup_common_bufsiz(); } while (0)
36 MAX_ENV = COMMON_BUFSIZE / sizeof(env[0]) - 1,
39 #ifndef SO_RCVBUFFORCE
40 #define SO_RCVBUFFORCE 33
42 enum { RCVBUF = 2 * 1024 * 1024 };
44 int uevent_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
45 int uevent_main(int argc UNUSED_PARAM, char **argv)
47 struct sockaddr_nl sa;
54 // Subscribe for UEVENT kernel messages
55 sa.nl_family = AF_NETLINK;
58 sa.nl_groups = 1 << 0;
59 fd = xsocket(AF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
60 xbind(fd, (struct sockaddr *) &sa, sizeof(sa));
63 // Without a sufficiently big RCVBUF, a ton of simultaneous events
64 // can trigger ENOBUFS on read, which is unrecoverable.
67 // find /sys -name uevent -exec sh -c 'echo add >"{}"' ';'
69 // SO_RCVBUFFORCE (root only) can go above net.core.rmem_max sysctl
70 setsockopt_SOL_SOCKET_int(fd, SO_RCVBUF, RCVBUF);
71 setsockopt_SOL_SOCKET_int(fd, SO_RCVBUFFORCE, RCVBUF);
74 socklen_t zl = sizeof(z);
75 getsockopt(fd, SOL_SOCKET, SO_RCVBUF, &z, &zl);
76 bb_error_msg("SO_RCVBUF:%d", z);
85 // In many cases, a system sits for *days* waiting
86 // for a new uevent notification to come in.
87 // We use a fresh mmap so that buffer is not allocated
88 // until kernel actually starts filling it.
89 netbuf = mmap(NULL, BUFFER_SIZE,
90 PROT_READ | PROT_WRITE,
91 MAP_PRIVATE | MAP_ANON,
92 /* ignored: */ -1, 0);
93 if (netbuf == MAP_FAILED)
94 bb_perror_msg_and_die("mmap");
96 // Here we block, possibly for a very long time
97 len = safe_read(fd, netbuf, BUFFER_SIZE - 1);
99 bb_perror_msg_and_die("read");
103 // Each netlink message starts with "ACTION@/path"
104 // (which we currently ignore),
105 // followed by environment variables.
113 if (strchr(s, '=') && idx < MAX_ENV)
123 spawn_and_wait(argv);
126 bb_unsetenv(env[idx++]);
127 munmap(netbuf, BUFFER_SIZE);
130 return 0; // not reached