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(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;
53 // Subscribe for UEVENT kernel messages
54 sa.nl_family = AF_NETLINK;
57 sa.nl_groups = 1 << 0;
58 fd = xsocket(AF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
59 xbind(fd, (struct sockaddr *) &sa, sizeof(sa));
62 // Without a sufficiently big RCVBUF, a ton of simultaneous events
63 // can trigger ENOBUFS on read, which is unrecoverable.
66 // find /sys -name uevent -exec sh -c 'echo add >"{}"' ';'
68 // SO_RCVBUFFORCE (root only) can go above net.core.rmem_max sysctl
69 setsockopt_SOL_SOCKET_int(fd, SO_RCVBUF, RCVBUF);
70 setsockopt_SOL_SOCKET_int(fd, SO_RCVBUFFORCE, RCVBUF);
73 socklen_t zl = sizeof(z);
74 getsockopt(fd, SOL_SOCKET, SO_RCVBUF, &z, &zl);
75 bb_error_msg("SO_RCVBUF:%d", z);
84 // In many cases, a system sits for *days* waiting
85 // for a new uevent notification to come in.
86 // We use a fresh mmap so that buffer is not allocated
87 // until kernel actually starts filling it.
88 netbuf = mmap(NULL, BUFFER_SIZE,
89 PROT_READ | PROT_WRITE,
90 MAP_PRIVATE | MAP_ANON,
91 /* ignored: */ -1, 0);
92 if (netbuf == MAP_FAILED)
93 bb_perror_msg_and_die("mmap");
95 // Here we block, possibly for a very long time
96 len = safe_read(fd, netbuf, BUFFER_SIZE - 1);
98 bb_perror_msg_and_die("read");
102 // Each netlink message starts with "ACTION@/path"
103 // (which we currently ignore),
104 // followed by environment variables.
112 if (strchr(s, '=') && idx < MAX_ENV)
122 spawn_and_wait(argv);
125 bb_unsetenv(env[idx++]);
126 munmap(netbuf, BUFFER_SIZE);
129 return 0; // not reached