2 * Copyright 2015 Denys Vlasenko
4 * Licensed under GPLv2, see file LICENSE in this source tree.
7 //config: bool "uevent (3.2 kb)"
9 //config: select PLATFORM_LINUX
11 //config: uevent is a netlink listener for kernel uevent notifications
12 //config: sent via netlink. It is usually used for dynamic device creation.
14 //applet:IF_UEVENT(APPLET(uevent, BB_DIR_SBIN, BB_SUID_DROP))
16 //kbuild:lib-$(CONFIG_UEVENT) += uevent.o
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"
27 #include "common_bufsiz.h"
28 #include <linux/netlink.h>
30 #define BUFFER_SIZE 16*1024
32 #define env ((char **)bb_common_bufsiz1)
33 #define INIT_G() do { setup_common_bufsiz(); } while (0)
35 MAX_ENV = COMMON_BUFSIZE / sizeof(char*) - 1,
36 /* sizeof(env[0]) instead of sizeof(char*)
37 * makes gcc-6.3.0 emit "strict-aliasing" warning.
41 #ifndef SO_RCVBUFFORCE
42 #define SO_RCVBUFFORCE 33
44 enum { RCVBUF = 2 * 1024 * 1024 };
46 int uevent_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
47 int uevent_main(int argc UNUSED_PARAM, char **argv)
49 struct sockaddr_nl sa;
56 // Subscribe for UEVENT kernel messages
57 sa.nl_family = AF_NETLINK;
60 sa.nl_groups = 1 << 0;
61 fd = xsocket(AF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
62 xbind(fd, (struct sockaddr *) &sa, sizeof(sa));
65 // Without a sufficiently big RCVBUF, a ton of simultaneous events
66 // can trigger ENOBUFS on read, which is unrecoverable.
69 // find /sys -name uevent -exec sh -c 'echo add >"{}"' ';'
71 // SO_RCVBUFFORCE (root only) can go above net.core.rmem_max sysctl
72 setsockopt_SOL_SOCKET_int(fd, SO_RCVBUF, RCVBUF);
73 setsockopt_SOL_SOCKET_int(fd, SO_RCVBUFFORCE, RCVBUF);
76 socklen_t zl = sizeof(z);
77 getsockopt(fd, SOL_SOCKET, SO_RCVBUF, &z, &zl);
78 bb_error_msg("SO_RCVBUF:%d", z);
87 // In many cases, a system sits for *days* waiting
88 // for a new uevent notification to come in.
89 // We use a fresh mmap so that buffer is not allocated
90 // until kernel actually starts filling it.
91 netbuf = mmap(NULL, BUFFER_SIZE,
92 PROT_READ | PROT_WRITE,
93 MAP_PRIVATE | MAP_ANON,
94 /* ignored: */ -1, 0);
95 if (netbuf == MAP_FAILED)
96 bb_perror_msg_and_die("mmap");
98 // Here we block, possibly for a very long time
99 len = safe_read(fd, netbuf, BUFFER_SIZE - 1);
101 bb_perror_msg_and_die("read");
105 // Each netlink message starts with "ACTION@/path"
106 // (which we currently ignore),
107 // followed by environment variables.
115 if (strchr(s, '=') && idx < MAX_ENV)
125 spawn_and_wait(argv);
128 bb_unsetenv(env[idx++]);
129 munmap(netbuf, BUFFER_SIZE);
132 return 0; // not reached