1 files changed, 120 insertions, 17 deletions

diff --git a/util-linux/mdev.c b/util-linux/mdev.c
index e730548f7..88c82b6fb 100644
--- a/util-linux/mdev.c
+++ b/util-linux/mdev.c
@@ -64,15 +64,30 @@
 //config:       These devices will request userspace look up the files in
 //config:       /lib/firmware/ and if it exists, send it to the kernel for
 //config:       loading into the hardware.
+//config:
+//config:config FEATURE_MDEV_DAEMON
+//config:       bool "Support daemon mode"
+//config:       default y
+//config:       depends on MDEV
+//config:       help
+//config:       Adds the -d option to run mdev in daemon mode handling hotplug
+//config:       events from the kernel like udev. If the system generates many
+//config:       hotplug events this mode of operation will consume less
+//config:       resources than registering mdev as hotplug helper or using the
+//config:       uevent applet.
 
 //applet:IF_MDEV(APPLET(mdev, BB_DIR_SBIN, BB_SUID_DROP))
 
 //kbuild:lib-$(CONFIG_MDEV) += mdev.o
 
 //usage:#define mdev_trivial_usage
-//usage:       "[-s]"
+//usage:       "[-s]" IF_FEATURE_MDEV_DAEMON(" | [-df]")
 //usage:#define mdev_full_usage "\n\n"
 //usage:       "mdev -s is to be run during boot to scan /sys and populate /dev.\n"
+//usage:        IF_FEATURE_MDEV_DAEMON(
+//usage:       "mdev -d[f]: daemon, listen on netlink.\n"
+//usage:       "        -f: stay in foreground.\n"
+//usage:        )
 //usage:       "\n"
 //usage:       "Bare mdev is a kernel hotplug helper. To activate it:\n"
 //usage:       "        echo /sbin/mdev >/proc/sys/kernel/hotplug\n"
@@ -98,6 +113,7 @@
 #include "libbb.h"
 #include "common_bufsiz.h"
 #include "xregex.h"
+#include <linux/netlink.h>
 
 /* "mdev -s" scans /sys/class/xxx, looking for directories which have dev
  * file (it is of the form "M:m\n"). Example: /sys/class/tty/tty0/dev
@@ -249,10 +265,9 @@
 #endif
 
 
-enum {
-        MDEV_OPT_SCAN       = 1 << 0,
-};
-
+#ifndef SO_RCVBUFFORCE
+#define SO_RCVBUFFORCE 33
+#endif
 static const char keywords[] ALIGN1 = "add\0remove\0"; // "change\0"
 enum { OP_add, OP_remove };
 
@@ -1051,7 +1066,7 @@ static void signal_mdevs(unsigned my_pid)
         }
 }
 
-static NOINLINE void process_action(char *temp, unsigned my_pid)
+static void process_action(char *temp, unsigned my_pid)
 {
         char *fw;
         char *seq;
@@ -1077,10 +1092,11 @@ static NOINLINE void process_action(char *temp, unsigned my_pid)
         seq = getenv("SEQNUM");
         op = index_in_strings(keywords, action);
 
-        open_mdev_log(seq, my_pid);
+        if (my_pid)
+                open_mdev_log(seq, my_pid);
 
         seq_fd = -1;
-        if (seq) {
+        if (my_pid && seq) {
                 seqnum = atoll(seq);
                 seq_fd = wait_for_seqfile(seqnum);
         }
@@ -1131,18 +1147,60 @@ static void initial_scan(char *temp)
                          fileAction, dirAction, temp, 0);
 }
 
+#if ENABLE_FEATURE_MDEV_DAEMON
+
+/* uevent applet uses 16k buffer, and mmaps it before every read */
+# define BUFFER_SIZE (2 * 1024)
+# define RCVBUF (2 * 1024 * 1024)
+# define MAX_ENV 32
+
+static void daemon_loop(char *temp, int fd)
+{
+        for (;;) {
+                char netbuf[BUFFER_SIZE];
+                char *env[MAX_ENV];
+                char *s, *end;
+                ssize_t len;
+                int idx;
+
+                len = safe_read(fd, netbuf, sizeof(netbuf) - 1);
+                if (len < 0) {
+                        bb_perror_msg_and_die("read");
+                }
+                end = netbuf + len;
+                *end = '\0';
+
+                idx = 0;
+                s = netbuf;
+                while (s < end && idx < MAX_ENV) {
+                        if (endofname(s)[0] == '=') {
+                                env[idx++] = s;
+                                putenv(s);
+                        }
+                        s += strlen(s) + 1;
+                }
+
+                process_action(temp, 0);
+
+                while (idx)
+                        bb_unsetenv(env[--idx]);
+        }
+}
+#endif
+
 int mdev_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int mdev_main(int argc UNUSED_PARAM, char **argv)
 {
+        enum {
+                MDEV_OPT_SCAN       = 1 << 0,
+                MDEV_OPT_DAEMON     = 1 << 1,
+                MDEV_OPT_FOREGROUND = 1 << 2,
+        };
         int opt;
         RESERVE_CONFIG_BUFFER(temp, PATH_MAX + SCRATCH_SIZE);
 
         INIT_G();
 
-#if ENABLE_FEATURE_MDEV_CONF
-        G.filename = "/etc/mdev.conf";
-#endif
-
         /* We can be called as hotplug helper */
         /* Kernel cannot provide suitable stdio fds for us, do it ourself */
         bb_sanitize_stdio();
@@ -1152,17 +1210,62 @@ int mdev_main(int argc UNUSED_PARAM, char **argv)
 
         xchdir("/dev");
 
-        opt = getopt32(argv, "s");
+        opt = getopt32(argv, "s" IF_FEATURE_MDEV_DAEMON("df"));
 
-        if (opt & MDEV_OPT_SCAN) {
-                /*
-                 * Scan: mdev -s
-                 */
 #if ENABLE_FEATURE_MDEV_CONF
+        G.filename = "/etc/mdev.conf";
+        if (opt & (MDEV_OPT_SCAN|MDEV_OPT_DAEMON)) {
                 /* Same as xrealloc_vector(NULL, 4, 0): */
                 G.rule_vec = xzalloc((1 << 4) * sizeof(*G.rule_vec));
+        }
 #endif
 
+#if ENABLE_FEATURE_MDEV_DAEMON
+        if (opt & MDEV_OPT_DAEMON) {
+                /*
+                 * Daemon mode listening on uevent netlink socket.
+                 */
+                struct sockaddr_nl sa;
+                int fd;
+
+//TODO: reuse same code in uevent
+                // 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:
+                //      mdev -d
+                //      find /sys -name uevent -exec sh -c 'echo add >"{}"' ';'
+                //
+                // SO_RCVBUFFORCE (root only) can go above net.core.rmem_max sysctl
+                setsockopt_SOL_SOCKET_int(fd, SO_RCVBUF,      RCVBUF);
+                setsockopt_SOL_SOCKET_int(fd, SO_RCVBUFFORCE, RCVBUF);
+
+                /*
+                 * Make inital scan after the uevent socket is alive and
+                 * _before_ we fork away.
+                 */
+                initial_scan(temp);
+
+                if (!(opt & MDEV_OPT_FOREGROUND))
+                        bb_daemonize_or_rexec(0, argv);
+
+                open_mdev_log(NULL, getpid());
+
+                daemon_loop(temp, fd);
+        }
+#endif
+        if (opt & MDEV_OPT_SCAN) {
+                /*
+                 * Scan: mdev -s
+                 */
                 initial_scan(temp);
         } else {
                 process_action(temp, getpid());