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authorGravatar Denys Vlasenko <vda.linux@googlemail.com>2015-04-16 12:44:02 +0200
committerGravatar Denys Vlasenko <vda.linux@googlemail.com>2015-04-16 12:44:02 +0200
commit71a5b67ba0339265153217df646827a1213e03f5 (patch)
tree1ed390d311f503f41b853d543d6edd4102047972 /util-linux
parentf7466e477691fd29f47ebe8ae27489e065c69e5e (diff)
downloadbusybox-71a5b67ba0339265153217df646827a1213e03f5.tar.gz
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uevent: new applet
This applet listens on netlink socket with kernel's uevent messages. Run-tested. function old new delta uevent_main - 416 +416 packed_usage 30671 30713 +42 applet_names 2531 2538 +7 applet_main 1468 1472 +4 RCVBUF - 4 +4 applet_nameofs 734 736 +2 ------------------------------------------------------------------------------ (add/remove: 3/0 grow/shrink: 4/0 up/down: 475/0) Total: 475 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'util-linux')
-rw-r--r--util-linux/uevent.c127
1 files changed, 127 insertions, 0 deletions
diff --git a/util-linux/uevent.c b/util-linux/uevent.c
new file mode 100644
index 000000000..fb98b4845
--- /dev/null
+++ b/util-linux/uevent.c
@@ -0,0 +1,127 @@
+/*
+ * 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
+}