Bump to version 1.22.1
[platform/upstream/busybox.git] / util-linux / mdev.c
index 17355bf..e80b58f 100644 (file)
@@ -80,7 +80,7 @@
 //usage:       IF_FEATURE_MDEV_CONF(
 //usage:       "\n"
 //usage:       "It uses /etc/mdev.conf with lines\n"
-//usage:       "       [-]DEVNAME UID:GID PERM"
+//usage:       "       [-][ENV=regex;]...DEVNAME UID:GID PERM"
 //usage:                       IF_FEATURE_MDEV_RENAME(" [>|=PATH]|[!]")
 //usage:                       IF_FEATURE_MDEV_EXEC(" [@|$|*PROG]")
 //usage:       "\n"
  * SUBSYSTEM=block
  */
 
-static const char keywords[] ALIGN1 = "add\0remove\0change\0";
+#define DEBUG_LVL 2
+
+#if DEBUG_LVL >= 1
+# define dbg1(...) do { if (G.verbose) bb_error_msg(__VA_ARGS__); } while(0)
+#else
+# define dbg1(...) ((void)0)
+#endif
+#if DEBUG_LVL >= 2
+# define dbg2(...) do { if (G.verbose >= 2) bb_error_msg(__VA_ARGS__); } while(0)
+#else
+# define dbg2(...) ((void)0)
+#endif
+#if DEBUG_LVL >= 3
+# define dbg3(...) do { if (G.verbose >= 3) bb_error_msg(__VA_ARGS__); } while(0)
+#else
+# define dbg3(...) ((void)0)
+#endif
+
+
+static const char keywords[] ALIGN1 = "add\0remove\0"; // "change\0"
 enum { OP_add, OP_remove };
 
+struct envmatch {
+       struct envmatch *next;
+       char *envname;
+       regex_t match;
+};
+
 struct rule {
        bool keep_matching;
        bool regex_compiled;
-       bool regex_has_slash;
        mode_t mode;
        int maj, min0, min1;
        struct bb_uidgid_t ugid;
@@ -244,12 +268,14 @@ struct rule {
        char *ren_mov;
        IF_FEATURE_MDEV_EXEC(char *r_cmd;)
        regex_t match;
+       struct envmatch *envmatch;
 };
 
 struct globals {
        int root_major, root_minor;
        smallint verbose;
        char *subsystem;
+       char *subsys_env; /* for putenv("SUBSYSTEM=subsystem") */
 #if ENABLE_FEATURE_MDEV_CONF
        const char *filename;
        parser_t *parser;
@@ -257,6 +283,7 @@ struct globals {
        unsigned rule_idx;
 #endif
        struct rule cur_rule;
+       char timestr[sizeof("60.123456")];
 } FIX_ALIASING;
 #define G (*(struct globals*)&bb_common_bufsiz1)
 #define INIT_G() do { \
@@ -268,15 +295,8 @@ struct globals {
 /* Prevent infinite loops in /sys symlinks */
 #define MAX_SYSFS_DEPTH 3
 
-/* We use additional 64+ bytes in make_device() */
-#define SCRATCH_SIZE 80
-
-#if 0
-# define dbg(...) bb_error_msg(__VA_ARGS__)
-#else
-# define dbg(...) ((void)0)
-#endif
-
+/* We use additional bytes in make_device() */
+#define SCRATCH_SIZE 128
 
 #if ENABLE_FEATURE_MDEV_CONF
 
@@ -289,14 +309,48 @@ static void make_default_cur_rule(void)
 
 static void clean_up_cur_rule(void)
 {
+       struct envmatch *e;
+
        free(G.cur_rule.envvar);
+       free(G.cur_rule.ren_mov);
        if (G.cur_rule.regex_compiled)
                regfree(&G.cur_rule.match);
-       free(G.cur_rule.ren_mov);
        IF_FEATURE_MDEV_EXEC(free(G.cur_rule.r_cmd);)
+       e = G.cur_rule.envmatch;
+       while (e) {
+               free(e->envname);
+               regfree(&e->match);
+               e = e->next;
+       }
        make_default_cur_rule();
 }
 
+static char *parse_envmatch_pfx(char *val)
+{
+       struct envmatch **nextp = &G.cur_rule.envmatch;
+
+       for (;;) {
+               struct envmatch *e;
+               char *semicolon;
+               char *eq = strchr(val, '=');
+               if (!eq /* || eq == val? */)
+                       return val;
+               if (endofname(val) != eq)
+                       return val;
+               semicolon = strchr(eq, ';');
+               if (!semicolon)
+                       return val;
+               /* ENVVAR=regex;... */
+               *nextp = e = xzalloc(sizeof(*e));
+               nextp = &e->next;
+               e->envname = xstrndup(val, eq - val);
+               *semicolon = '\0';
+               xregcomp(&e->match, eq + 1, REG_EXTENDED);
+               *semicolon = ';';
+               val = semicolon + 1;
+       }
+}
+
 static void parse_next_rule(void)
 {
        /* Note: on entry, G.cur_rule is set to default */
@@ -309,12 +363,13 @@ static void parse_next_rule(void)
                        break;
 
                /* Fields: [-]regex uid:gid mode [alias] [cmd] */
-               dbg("token1:'%s'", tokens[1]);
+               dbg3("token1:'%s'", tokens[1]);
 
                /* 1st field */
                val = tokens[0];
                G.cur_rule.keep_matching = ('-' == val[0]);
                val += G.cur_rule.keep_matching; /* swallow leading dash */
+               val = parse_envmatch_pfx(val);
                if (val[0] == '@') {
                        /* @major,minor[-minor2] */
                        /* (useful when name is ambiguous:
@@ -329,8 +384,10 @@ static void parse_next_rule(void)
                        if (sc == 2)
                                G.cur_rule.min1 = G.cur_rule.min0;
                } else {
+                       char *eq = strchr(val, '=');
                        if (val[0] == '$') {
-                               char *eq = strchr(++val, '=');
+                               /* $ENVVAR=regex ... */
+                               val++;
                                if (!eq) {
                                        bb_error_msg("bad $envvar=regex on line %d", G.parser->lineno);
                                        goto next_rule;
@@ -340,7 +397,6 @@ static void parse_next_rule(void)
                        }
                        xregcomp(&G.cur_rule.match, val, REG_EXTENDED);
                        G.cur_rule.regex_compiled = 1;
-                       G.cur_rule.regex_has_slash = (strchr(val, '/') != NULL);
                }
 
                /* 2nd field: uid:gid - device ownership */
@@ -375,7 +431,7 @@ static void parse_next_rule(void)
                clean_up_cur_rule();
        } /* while (config_read) */
 
-       dbg("config_close(G.parser)");
+       dbg3("config_close(G.parser)");
        config_close(G.parser);
        G.parser = NULL;
 
@@ -392,7 +448,7 @@ static const struct rule *next_rule(void)
 
        /* Open conf file if we didn't do it yet */
        if (!G.parser && G.filename) {
-               dbg("config_open('%s')", G.filename);
+               dbg3("config_open('%s')", G.filename);
                G.parser = config_open2(G.filename, fopen_for_read);
                G.filename = NULL;
        }
@@ -401,7 +457,7 @@ static const struct rule *next_rule(void)
                /* mdev -s */
                /* Do we have rule parsed already? */
                if (G.rule_vec[G.rule_idx]) {
-                       dbg("< G.rule_vec[G.rule_idx:%d]=%p", G.rule_idx, G.rule_vec[G.rule_idx]);
+                       dbg3("< G.rule_vec[G.rule_idx:%d]=%p", G.rule_idx, G.rule_vec[G.rule_idx]);
                        return G.rule_vec[G.rule_idx++];
                }
                make_default_cur_rule();
@@ -418,19 +474,46 @@ static const struct rule *next_rule(void)
                        rule = memcpy(xmalloc(sizeof(G.cur_rule)), &G.cur_rule, sizeof(G.cur_rule));
                        G.rule_vec = xrealloc_vector(G.rule_vec, 4, G.rule_idx);
                        G.rule_vec[G.rule_idx++] = rule;
-                       dbg("> G.rule_vec[G.rule_idx:%d]=%p", G.rule_idx, G.rule_vec[G.rule_idx]);
+                       dbg3("> G.rule_vec[G.rule_idx:%d]=%p", G.rule_idx, G.rule_vec[G.rule_idx]);
                }
        }
 
        return rule;
 }
 
+static int env_matches(struct envmatch *e)
+{
+       while (e) {
+               int r;
+               char *val = getenv(e->envname);
+               if (!val)
+                       return 0;
+               r = regexec(&e->match, val, /*size*/ 0, /*range[]*/ NULL, /*eflags*/ 0);
+               if (r != 0) /* no match */
+                       return 0;
+               e = e->next;
+       }
+       return 1;
+}
+
 #else
 
 # define next_rule() (&G.cur_rule)
 
 #endif
 
+static void mkdir_recursive(char *name)
+{
+       /* if name has many levels ("dir1/dir2"),
+        * bb_make_directory() will create dir1 according to umask,
+        * not according to its "mode" parameter.
+        * Since we run with umask=0, need to temporarily switch it.
+        */
+       umask(022); /* "dir1" (if any) will be 0755 too */
+       bb_make_directory(name, 0755, FILEUTILS_RECUR);
+       umask(0);
+}
+
 /* Builds an alias path.
  * This function potentionally reallocates the alias parameter.
  * Only used for ENABLE_FEATURE_MDEV_RENAME
@@ -444,7 +527,7 @@ static char *build_alias(char *alias, const char *device_name)
        dest = strrchr(alias, '/');
        if (dest) { /* ">bar/[baz]" ? */
                *dest = '\0'; /* mkdir bar */
-               bb_make_directory(alias, 0755, FILEUTILS_RECUR);
+               mkdir_recursive(alias);
                *dest = '/';
                if (dest[1] == '\0') { /* ">bar/" => ">bar/device_name" */
                        dest = alias;
@@ -458,7 +541,7 @@ static char *build_alias(char *alias, const char *device_name)
 
 /* mknod in /dev based on a path like "/sys/block/hda/hda1"
  * NB1: path parameter needs to have SCRATCH_SIZE scratch bytes
- * after NUL, but we promise to not mangle (IOW: to restore if needed)
+ * after NUL, but we promise to not mangle (IOW: to restore NUL if needed)
  * path string.
  * NB2: "mdev -s" may call us many times, do not leak memory/fds!
  *
@@ -467,11 +550,8 @@ static char *build_alias(char *alias, const char *device_name)
  */
 static void make_device(char *device_name, char *path, int operation)
 {
-       char *subsystem_slash_devname;
        int major, minor, type, len;
-
-       if (G.verbose)
-               bb_error_msg("make_device: %s, %s, op:%d", device_name, path, operation);
+       char *path_end = path + strlen(path);
 
        /* Try to read major/minor string.  Note that the kernel puts \n after
         * the data, so we don't need to worry about null terminating the string
@@ -479,52 +559,60 @@ static void make_device(char *device_name, char *path, int operation)
         * We also depend on path having writeable space after it.
         */
        major = -1;
-       if (operation != OP_remove) {
-               char *dev_maj_min = path + strlen(path);
-
-               strcpy(dev_maj_min, "/dev");
-               len = open_read_close(path, dev_maj_min + 1, 64);
-               *dev_maj_min = '\0';
+       if (operation == OP_add) {
+               strcpy(path_end, "/dev");
+               len = open_read_close(path, path_end + 1, SCRATCH_SIZE - 1);
+               *path_end = '\0';
                if (len < 1) {
                        if (!ENABLE_FEATURE_MDEV_EXEC)
                                return;
                        /* no "dev" file, but we can still run scripts
                         * based on device name */
-               } else if (sscanf(++dev_maj_min, "%u:%u", &major, &minor) != 2) {
+               } else if (sscanf(path_end + 1, "%u:%u", &major, &minor) == 2) {
+                       dbg1("dev %u,%u", major, minor);
+               } else {
                        major = -1;
                }
        }
        /* else: for delete, -1 still deletes the node, but < -1 suppresses that */
 
-       /* Determine device name, type, major and minor */
-       if (!device_name)
-               device_name = (char*) bb_basename(path);
-       /* http://kernel.org/doc/pending/hotplug.txt says that only
+       /* Determine device name */
+       if (!device_name) {
+               /*
+                * There was no $DEVNAME envvar (for example, mdev -s never has).
+                * But it is very useful: it contains the *path*, not only basename,
+                * Thankfully, uevent file has it.
+                * Example of .../sound/card0/controlC0/uevent file on Linux-3.7.7:
+                * MAJOR=116
+                * MINOR=7
+                * DEVNAME=snd/controlC0
+                */
+               strcpy(path_end, "/uevent");
+               len = open_read_close(path, path_end + 1, SCRATCH_SIZE - 1);
+               if (len < 0)
+                       len = 0;
+               *path_end = '\0';
+               path_end[1 + len] = '\0';
+               device_name = strstr(path_end + 1, "\nDEVNAME=");
+               if (device_name) {
+                       device_name += sizeof("\nDEVNAME=")-1;
+                       strchrnul(device_name, '\n')[0] = '\0';
+               } else {
+                       /* Fall back to just basename */
+                       device_name = (char*) bb_basename(path);
+               }
+       }
+       /* Determine device type */
+       /*
+        * http://kernel.org/doc/pending/hotplug.txt says that only
         * "/sys/block/..." is for block devices. "/sys/bus" etc is not.
         * But since 2.6.25 block devices are also in /sys/class/block.
-        * We use strstr("/block/") to forestall future surprises. */
+        * We use strstr("/block/") to forestall future surprises.
+        */
        type = S_IFCHR;
        if (strstr(path, "/block/") || (G.subsystem && strncmp(G.subsystem, "block", 5) == 0))
                type = S_IFBLK;
 
-       /* Make path point to "subsystem/device_name" */
-       subsystem_slash_devname = NULL;
-       /* Check for coldplug invocations first */
-       if (strncmp(path, "/sys/block/", 11) == 0) /* legacy case */
-               path += sizeof("/sys/") - 1;
-       else if (strncmp(path, "/sys/class/", 11) == 0)
-               path += sizeof("/sys/class/") - 1;
-       else {
-               /* Example of a hotplug invocation:
-                * SUBSYSTEM="block"
-                * DEVPATH="/sys" + "/devices/virtual/mtd/mtd3/mtdblock3"
-                * ("/sys" is added by mdev_main)
-                * - path does not contain subsystem
-                */
-               subsystem_slash_devname = concat_path_file(G.subsystem, device_name);
-               path = subsystem_slash_devname;
-       }
-
 #if ENABLE_FEATURE_MDEV_CONF
        G.rule_idx = 0; /* restart from the beginning (think mdev -s) */
 #endif
@@ -537,11 +625,13 @@ static void make_device(char *device_name, char *path, int operation)
                char *node_name;
                const struct rule *rule;
 
-               str_to_match = "";
+               str_to_match = device_name;
 
                rule = next_rule();
 
 #if ENABLE_FEATURE_MDEV_CONF
+               if (!env_matches(rule->envmatch))
+                       continue;
                if (rule->maj >= 0) {  /* @maj,min rule */
                        if (major != rule->maj)
                                continue;
@@ -552,19 +642,15 @@ static void make_device(char *device_name, char *path, int operation)
                }
                if (rule->envvar) { /* $envvar=regex rule */
                        str_to_match = getenv(rule->envvar);
-                       dbg("getenv('%s'):'%s'", rule->envvar, str_to_match);
+                       dbg3("getenv('%s'):'%s'", rule->envvar, str_to_match);
                        if (!str_to_match)
                                continue;
-               } else {
-//TODO: $DEVNAME can have slashes too,
-// we should stop abusing '/' as a special syntax in our regex'es
-                       /* regex to match [subsystem/]device_name */
-                       str_to_match = (rule->regex_has_slash ? path : device_name);
                }
+               /* else: str_to_match = device_name */
 
                if (rule->regex_compiled) {
                        int regex_match = regexec(&rule->match, str_to_match, ARRAY_SIZE(off), off, 0);
-                       dbg("regex_match for '%s':%d", str_to_match, regex_match);
+                       dbg3("regex_match for '%s':%d", str_to_match, regex_match);
                        //bb_error_msg("matches:");
                        //for (int i = 0; i < ARRAY_SIZE(off); i++) {
                        //      if (off[i].rm_so < 0) continue;
@@ -583,9 +669,8 @@ static void make_device(char *device_name, char *path, int operation)
                }
                /* else: it's final implicit "match-all" rule */
  rule_matches:
+               dbg2("rule matched, line %d", G.parser ? G.parser->lineno : -1);
 #endif
-               dbg("rule matched");
-
                /* Build alias name */
                alias = NULL;
                if (ENABLE_FEATURE_MDEV_RENAME && rule->ren_mov) {
@@ -628,60 +713,64 @@ static void make_device(char *device_name, char *path, int operation)
                                }
                        }
                }
-               dbg("alias:'%s'", alias);
+               dbg3("alias:'%s'", alias);
 
                command = NULL;
                IF_FEATURE_MDEV_EXEC(command = rule->r_cmd;)
                if (command) {
-                       const char *s = "$@*";
-                       const char *s2 = strchr(s, command[0]);
-
                        /* Are we running this command now?
-                        * Run $cmd on delete, @cmd on create, *cmd on both
+                        * Run @cmd on create, $cmd on delete, *cmd on any
                         */
-                       if (s2 - s != (operation == OP_remove) || *s2 == '*') {
-                               /* We are here if: '*',
-                                * or: '@' and delete = 0,
-                                * or: '$' and delete = 1
-                                */
+                       if ((command[0] == '@' && operation == OP_add)
+                        || (command[0] == '$' && operation == OP_remove)
+                        || (command[0] == '*')
+                       ) {
                                command++;
                        } else {
                                command = NULL;
                        }
                }
-               dbg("command:'%s'", command);
+               dbg3("command:'%s'", command);
 
                /* "Execute" the line we found */
                node_name = device_name;
                if (ENABLE_FEATURE_MDEV_RENAME && alias) {
                        node_name = alias = build_alias(alias, device_name);
-                       dbg("alias2:'%s'", alias);
+                       dbg3("alias2:'%s'", alias);
                }
 
                if (operation == OP_add && major >= 0) {
                        char *slash = strrchr(node_name, '/');
                        if (slash) {
                                *slash = '\0';
-                               bb_make_directory(node_name, 0755, FILEUTILS_RECUR);
+                               mkdir_recursive(node_name);
                                *slash = '/';
                        }
-                       if (G.verbose)
-                               bb_error_msg("mknod: %s (%d,%d) %o", node_name, major, minor, rule->mode | type);
+                       if (ENABLE_FEATURE_MDEV_CONF) {
+                               dbg1("mknod %s (%d,%d) %o"
+                                       " %u:%u",
+                                       node_name, major, minor, rule->mode | type,
+                                       rule->ugid.uid, rule->ugid.gid
+                               );
+                       } else {
+                               dbg1("mknod %s (%d,%d) %o",
+                                       node_name, major, minor, rule->mode | type
+                               );
+                       }
                        if (mknod(node_name, rule->mode | type, makedev(major, minor)) && errno != EEXIST)
                                bb_perror_msg("can't create '%s'", node_name);
-                       if (major == G.root_major && minor == G.root_minor)
-                               symlink(node_name, "root");
                        if (ENABLE_FEATURE_MDEV_CONF) {
                                chmod(node_name, rule->mode);
                                chown(node_name, rule->ugid.uid, rule->ugid.gid);
                        }
+                       if (major == G.root_major && minor == G.root_minor)
+                               symlink(node_name, "root");
                        if (ENABLE_FEATURE_MDEV_RENAME && alias) {
                                if (aliaslink == '>') {
 //TODO: on devtmpfs, device_name already exists and symlink() fails.
 //End result is that instead of symlink, we have two nodes.
 //What should be done?
-                                       if (G.verbose)
-                                               bb_error_msg("symlink: %s", device_name);
+                                       dbg1("symlink: %s", device_name);
                                        symlink(node_name, device_name);
                                }
                        }
@@ -690,27 +779,21 @@ static void make_device(char *device_name, char *path, int operation)
                if (ENABLE_FEATURE_MDEV_EXEC && command) {
                        /* setenv will leak memory, use putenv/unsetenv/free */
                        char *s = xasprintf("%s=%s", "MDEV", node_name);
-                       char *s1 = xasprintf("%s=%s", "SUBSYSTEM", G.subsystem);
                        putenv(s);
-                       putenv(s1);
-                       if (G.verbose)
-                               bb_error_msg("running: %s", command);
+                       dbg1("running: %s", command);
                        if (system(command) == -1)
                                bb_perror_msg("can't run '%s'", command);
-                       bb_unsetenv_and_free(s1);
                        bb_unsetenv_and_free(s);
                }
 
                if (operation == OP_remove && major >= -1) {
                        if (ENABLE_FEATURE_MDEV_RENAME && alias) {
                                if (aliaslink == '>') {
-                                       if (G.verbose)
-                                               bb_error_msg("unlink: %s", device_name);
+                                       dbg1("unlink: %s", device_name);
                                        unlink(device_name);
                                }
                        }
-                       if (G.verbose)
-                               bb_error_msg("unlink: %s", node_name);
+                       dbg1("unlink: %s", node_name);
                        unlink(node_name);
                }
 
@@ -723,8 +806,6 @@ static void make_device(char *device_name, char *path, int operation)
                if (!ENABLE_FEATURE_MDEV_CONF || !rule->keep_matching)
                        break;
        } /* for (;;) */
-
-       free(subsystem_slash_devname);
 }
 
 /* File callback for /sys/ traversal */
@@ -757,9 +838,16 @@ static int FAST_FUNC dirAction(const char *fileName UNUSED_PARAM,
         * under /sys/class/ */
        if (1 == depth) {
                free(G.subsystem);
+               if (G.subsys_env) {
+                       bb_unsetenv_and_free(G.subsys_env);
+                       G.subsys_env = NULL;
+               }
                G.subsystem = strrchr(fileName, '/');
-               if (G.subsystem)
+               if (G.subsystem) {
                        G.subsystem = xstrdup(G.subsystem + 1);
+                       G.subsys_env = xasprintf("%s=%s", "SUBSYSTEM", G.subsystem);
+                       putenv(G.subsys_env);
+               }
        }
 
        return (depth >= MAX_SYSFS_DEPTH ? SKIP : TRUE);
@@ -779,47 +867,149 @@ static int FAST_FUNC dirAction(const char *fileName UNUSED_PARAM,
 static void load_firmware(const char *firmware, const char *sysfs_path)
 {
        int cnt;
-       int firmware_fd, loading_fd, data_fd;
+       int firmware_fd, loading_fd;
 
        /* check for /lib/firmware/$FIRMWARE */
        xchdir("/lib/firmware");
-       firmware_fd = xopen(firmware, O_RDONLY);
-
-       /* in case we goto out ... */
-       data_fd = -1;
+       firmware_fd = open(firmware, O_RDONLY); /* can fail */
 
        /* check for /sys/$DEVPATH/loading ... give 30 seconds to appear */
        xchdir(sysfs_path);
        for (cnt = 0; cnt < 30; ++cnt) {
                loading_fd = open("loading", O_WRONLY);
-               if (loading_fd != -1)
+               if (loading_fd >= 0)
                        goto loading;
                sleep(1);
        }
        goto out;
 
  loading:
-       /* tell kernel we're loading by "echo 1 > /sys/$DEVPATH/loading" */
-       if (full_write(loading_fd, "1", 1) != 1)
-               goto out;
-
-       /* load firmware into /sys/$DEVPATH/data */
-       data_fd = open("data", O_WRONLY);
-       if (data_fd == -1)
-               goto out;
-       cnt = bb_copyfd_eof(firmware_fd, data_fd);
+       cnt = 0;
+       if (firmware_fd >= 0) {
+               int data_fd;
+
+               /* tell kernel we're loading by "echo 1 > /sys/$DEVPATH/loading" */
+               if (full_write(loading_fd, "1", 1) != 1)
+                       goto out;
+
+               /* load firmware into /sys/$DEVPATH/data */
+               data_fd = open("data", O_WRONLY);
+               if (data_fd < 0)
+                       goto out;
+               cnt = bb_copyfd_eof(firmware_fd, data_fd);
+               if (ENABLE_FEATURE_CLEAN_UP)
+                       close(data_fd);
+       }
 
-       /* tell kernel result by "echo [0|-1] > /sys/$DEVPATH/loading" */
+       /* Tell kernel result by "echo [0|-1] > /sys/$DEVPATH/loading"
+        * Note: we emit -1 also if firmware file wasn't found.
+        * There are cases when otherwise kernel would wait for minutes
+        * before timing out.
+        */
        if (cnt > 0)
                full_write(loading_fd, "0", 1);
        else
                full_write(loading_fd, "-1", 2);
 
  out:
+       xchdir("/dev");
        if (ENABLE_FEATURE_CLEAN_UP) {
                close(firmware_fd);
                close(loading_fd);
-               close(data_fd);
+       }
+}
+
+static char *curtime(void)
+{
+       struct timeval tv;
+       gettimeofday(&tv, NULL);
+       sprintf(G.timestr, "%u.%06u", (unsigned)tv.tv_sec % 60, (unsigned)tv.tv_usec);
+       return G.timestr;
+}
+
+static void open_mdev_log(const char *seq, unsigned my_pid)
+{
+       int logfd = open("mdev.log", O_WRONLY | O_APPEND);
+       if (logfd >= 0) {
+               xmove_fd(logfd, STDERR_FILENO);
+               G.verbose = 2;
+               applet_name = xasprintf("%s[%s]", applet_name, seq ? seq : utoa(my_pid));
+       }
+}
+
+/* If it exists, does /dev/mdev.seq match $SEQNUM?
+ * If it does not match, earlier mdev is running
+ * in parallel, and we need to wait.
+ * Active mdev pokes us with SIGCHLD to check the new file.
+ */
+static int
+wait_for_seqfile(const char *seq)
+{
+       /* We time out after 2 sec */
+       static const struct timespec ts = { 0, 32*1000*1000 };
+       int timeout = 2000 / 32;
+       int seq_fd = -1;
+       int do_once = 1;
+       sigset_t set_CHLD;
+
+       sigemptyset(&set_CHLD);
+       sigaddset(&set_CHLD, SIGCHLD);
+       sigprocmask(SIG_BLOCK, &set_CHLD, NULL);
+
+       for (;;) {
+               int seqlen;
+               char seqbuf[sizeof(int)*3 + 2];
+
+               if (seq_fd < 0) {
+                       seq_fd = open("mdev.seq", O_RDWR);
+                       if (seq_fd < 0)
+                               break;
+               }
+               seqlen = pread(seq_fd, seqbuf, sizeof(seqbuf) - 1, 0);
+               if (seqlen < 0) {
+                       close(seq_fd);
+                       seq_fd = -1;
+                       break;
+               }
+               seqbuf[seqlen] = '\0';
+               if (seqbuf[0] == '\n') {
+                       /* seed file: write out seq ASAP */
+                       xwrite_str(seq_fd, seq);
+                       xlseek(seq_fd, 0, SEEK_SET);
+                       dbg2("first seq written");
+                       break;
+               }
+               if (strcmp(seq, seqbuf) == 0) {
+                       /* correct idx */
+                       break;
+               }
+               if (do_once) {
+                       dbg2("%s waiting for '%s'", curtime(), seqbuf);
+                       do_once = 0;
+               }
+               if (sigtimedwait(&set_CHLD, NULL, &ts) >= 0) {
+                       dbg3("woken up");
+                       continue; /* don't decrement timeout! */
+               }
+               if (--timeout == 0) {
+                       dbg1("%s waiting for '%s'", "timed out", seqbuf);
+                       break;
+               }
+       }
+       sigprocmask(SIG_UNBLOCK, &set_CHLD, NULL);
+       return seq_fd;
+}
+
+static void signal_mdevs(unsigned my_pid)
+{
+       procps_status_t* p = NULL;
+       while ((p = procps_scan(p, PSSCAN_ARGV0)) != NULL) {
+               if (p->pid != my_pid
+                && p->argv0
+                && strcmp(bb_basename(p->argv0), "mdev") == 0
+               ) {
+                       kill(p->pid, SIGCHLD);
+               }
        }
 }
 
@@ -844,8 +1034,8 @@ int mdev_main(int argc UNUSED_PARAM, char **argv)
        xchdir("/dev");
 
        if (argv[1] && strcmp(argv[1], "-s") == 0) {
-               /* Scan:
-                * mdev -s
+               /*
+                * Scan: mdev -s
                 */
                struct stat st;
 
@@ -857,6 +1047,8 @@ int mdev_main(int argc UNUSED_PARAM, char **argv)
                G.root_major = major(st.st_dev);
                G.root_minor = minor(st.st_dev);
 
+               putenv((char*)"ACTION=add");
+
                /* ACTION_FOLLOWLINKS is needed since in newer kernels
                 * /sys/block/loop* (for example) are symlinks to dirs,
                 * not real directories.
@@ -882,54 +1074,37 @@ int mdev_main(int argc UNUSED_PARAM, char **argv)
                char *action;
                char *env_devname;
                char *env_devpath;
+               unsigned my_pid;
+               int seq_fd;
                smalluint op;
 
                /* Hotplug:
                 * env ACTION=... DEVPATH=... SUBSYSTEM=... [SEQNUM=...] mdev
-                * ACTION can be "add" or "remove"
+                * ACTION can be "add", "remove", "change"
                 * DEVPATH is like "/block/sda" or "/class/input/mice"
                 */
-               action = getenv("ACTION");
                env_devname = getenv("DEVNAME"); /* can be NULL */
-               env_devpath = getenv("DEVPATH");
                G.subsystem = getenv("SUBSYSTEM");
+               action = getenv("ACTION");
+               env_devpath = getenv("DEVPATH");
                if (!action || !env_devpath /*|| !G.subsystem*/)
                        bb_show_usage();
                fw = getenv("FIRMWARE");
-               op = index_in_strings(keywords, action);
-               /* If it exists, does /dev/mdev.seq match $SEQNUM?
-                * If it does not match, earlier mdev is running
-                * in parallel, and we need to wait */
                seq = getenv("SEQNUM");
-               if (seq) {
-                       int timeout = 2000 / 32; /* 2000 msec */
-                       do {
-                               int seqlen;
-                               char seqbuf[sizeof(int)*3 + 2];
-
-                               seqlen = open_read_close("mdev.seq", seqbuf, sizeof(seqbuf) - 1);
-                               if (seqlen < 0) {
-                                       seq = NULL;
-                                       break;
-                               }
-                               seqbuf[seqlen] = '\0';
-                               if (seqbuf[0] == '\n' /* seed file? */
-                                || strcmp(seq, seqbuf) == 0 /* correct idx? */
-                               ) {
-                                       break;
-                               }
-                               usleep(32*1000);
-                       } while (--timeout);
-               }
+               op = index_in_strings(keywords, action);
 
-               {
-                       int logfd = open("/dev/mdev.log", O_WRONLY | O_APPEND);
-                       if (logfd >= 0) {
-                               xmove_fd(logfd, STDERR_FILENO);
-                               G.verbose = 1;
-                               bb_error_msg("pid: %u seq: %s action: %s", getpid(), seq, action);
-                       }
-               }
+               my_pid = getpid();
+               open_mdev_log(seq, my_pid);
+
+               seq_fd = seq ? wait_for_seqfile(seq) : -1;
+
+               dbg1("%s "
+                       "ACTION:%s SUBSYSTEM:%s DEVNAME:%s DEVPATH:%s"
+                       "%s%s",
+                       curtime(),
+                       action, G.subsystem, env_devname, env_devpath,
+                       fw ? " FW:" : "", fw ? fw : ""
+               );
 
                snprintf(temp, PATH_MAX, "/sys%s", env_devpath);
                if (op == OP_remove) {
@@ -939,16 +1114,18 @@ int mdev_main(int argc UNUSED_PARAM, char **argv)
                        if (!fw)
                                make_device(env_devname, temp, op);
                }
-               else if (op == OP_add) {
+               else {
                        make_device(env_devname, temp, op);
                        if (ENABLE_FEATURE_MDEV_LOAD_FIRMWARE) {
-                               if (fw)
+                               if (op == OP_add && fw)
                                        load_firmware(fw, temp);
                        }
                }
 
-               if (seq) {
-                       xopen_xwrite_close("mdev.seq", utoa(xatou(seq) + 1));
+               dbg1("%s exiting", curtime());
+               if (seq_fd >= 0) {
+                       xwrite_str(seq_fd, utoa(xatou(seq) + 1));
+                       signal_mdevs(my_pid);
                }
        }