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/*
* Copyright 2015 Denys Vlasenko
*
* Licensed under GPLv2, see file LICENSE in this source tree.
*/
//config:config UEVENT
//config: bool "uevent"
//config: default y
//config: select PLATFORM_LINUX
//config: help
//config: uevent is a netlink listener for kernel uevent notifications
//config: sent via netlink. It is usually used for dynamic device creation.
//applet:IF_UEVENT(APPLET(uevent, BB_DIR_SBIN, BB_SUID_DROP))
//kbuild:lib-$(CONFIG_UEVENT) += uevent.o
//usage:#define uevent_trivial_usage
//usage: "[PROG [ARGS]]"
//usage:#define uevent_full_usage "\n\n"
//usage: "uevent runs PROG for every netlink notification."
//usage: "\n""PROG's environment contains data passed from the kernel."
//usage: "\n""Typical usage (daemon for dynamic device node creation):"
//usage: "\n"" # uevent mdev & mdev -s"
#include "libbb.h"
#include <linux/netlink.h>
#define BUFFER_SIZE 16*1024
#define env ((char **)&bb_common_bufsiz1)
enum {
MAX_ENV = COMMON_BUFSIZE / sizeof(env[0]) - 1,
};
#ifndef SO_RCVBUFFORCE
#define SO_RCVBUFFORCE 33
#endif
static const int RCVBUF = 2 * 1024 * 1024;
int uevent_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int uevent_main(int argc UNUSED_PARAM, char **argv)
{
struct sockaddr_nl sa;
int fd;
argv++;
// Subscribe for UEVENT kernel messages
sa.nl_family = AF_NETLINK;
sa.nl_pad = 0;
sa.nl_pid = getpid();
sa.nl_groups = 1 << 0;
fd = xsocket(AF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
xbind(fd, (struct sockaddr *) &sa, sizeof(sa));
close_on_exec_on(fd);
// Without a sufficiently big RCVBUF, a ton of simultaneous events
// can trigger ENOBUFS on read, which is unrecoverable.
// Reproducer:
// uevent mdev &
// find /sys -name uevent -exec sh -c 'echo add >"{}"' ';'
//
// SO_RCVBUFFORCE (root only) can go above net.core.rmem_max sysctl
setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &RCVBUF, sizeof(RCVBUF));
setsockopt(fd, SOL_SOCKET, SO_RCVBUFFORCE, &RCVBUF, sizeof(RCVBUF));
if (0) {
int z;
socklen_t zl = sizeof(z);
getsockopt(fd, SOL_SOCKET, SO_RCVBUF, &z, &zl);
bb_error_msg("SO_RCVBUF:%d", z);
}
for (;;) {
char *netbuf;
char *s, *end;
ssize_t len;
int idx;
// In many cases, a system sits for *days* waiting
// for a new uevent notification to come in.
// We use a fresh mmap so that buffer is not allocated
// until kernel actually starts filling it.
netbuf = mmap(NULL, BUFFER_SIZE,
PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANON,
/* ignored: */ -1, 0);
if (netbuf == MAP_FAILED)
bb_perror_msg_and_die("mmap");
// Here we block, possibly for a very long time
len = safe_read(fd, netbuf, BUFFER_SIZE - 1);
if (len < 0)
bb_perror_msg_and_die("read");
end = netbuf + len;
*end = '\0';
// Each netlink message starts with "ACTION@/path"
// (which we currently ignore),
// followed by environment variables.
if (!argv[0])
putchar('\n');
idx = 0;
s = netbuf;
while (s < end) {
if (!argv[0])
puts(s);
if (strchr(s, '=') && idx < MAX_ENV)
env[idx++] = s;
s += strlen(s) + 1;
}
env[idx] = NULL;
idx = 0;
while (env[idx])
putenv(env[idx++]);
if (argv[0])
spawn_and_wait(argv);
idx = 0;
while (env[idx])
bb_unsetenv(env[idx++]);
munmap(netbuf, BUFFER_SIZE);
}
return 0; // not reached
}
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