2 * Copyright 2015 Denys Vlasenko
4 * Licensed under GPLv2, see file LICENSE in this source tree.
7 //config: bool "uevent (3.1 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)
55 // Subscribe for UEVENT kernel messages.
56 // Without a sufficiently big RCVBUF, a ton of simultaneous events
57 // can trigger ENOBUFS on read, which is unrecoverable.
60 // find /sys -name uevent -exec sh -c 'echo add >"{}"' ';'
61 fd = create_and_bind_to_netlink(NETLINK_KOBJECT_UEVENT, /*groups:*/ 1 << 0, RCVBUF);
69 // In many cases, a system sits for *days* waiting
70 // for a new uevent notification to come in.
71 // We use a fresh mmap so that buffer is not allocated
72 // until kernel actually starts filling it.
73 netbuf = mmap(NULL, BUFFER_SIZE,
74 PROT_READ | PROT_WRITE,
75 MAP_PRIVATE | MAP_ANON,
76 /* ignored: */ -1, 0);
77 if (netbuf == MAP_FAILED)
78 bb_simple_perror_msg_and_die("mmap");
80 // Here we block, possibly for a very long time
81 len = safe_read(fd, netbuf, BUFFER_SIZE - 1);
83 bb_simple_perror_msg_and_die("read");
87 // Each netlink message starts with "ACTION@/path"
88 // (which we currently ignore),
89 // followed by environment variables.
97 if (strchr(s, '=') && idx < MAX_ENV)
107 spawn_and_wait(argv);
110 bb_unsetenv(env[idx++]);
112 munmap(netbuf, BUFFER_SIZE);
115 return 0; // not reached