/* vi: set sw=4 ts=4: */
/*
 * mdev - Mini udev for busybox
 *
 * Copyright 2005 Rob Landley <rob@landley.net>
 * Copyright 2005 Frank Sorenson <frank@tuxrocks.com>
 *
 * Licensed under GPLv2, see file LICENSE in this source tree.
 */
//config:config MDEV
//config:       bool "mdev (17 kb)"
//config:       default y
//config:       select PLATFORM_LINUX
//config:       help
//config:       mdev is a mini-udev implementation for dynamically creating device
//config:       nodes in the /dev directory.
//config:
//config:       For more information, please see docs/mdev.txt
//config:
//config:config FEATURE_MDEV_CONF
//config:       bool "Support /etc/mdev.conf"
//config:       default y
//config:       depends on MDEV
//config:       help
//config:       Add support for the mdev config file to control ownership and
//config:       permissions of the device nodes.
//config:
//config:       For more information, please see docs/mdev.txt
//config:
//config:config FEATURE_MDEV_RENAME
//config:       bool "Support subdirs/symlinks"
//config:       default y
//config:       depends on FEATURE_MDEV_CONF
//config:       help
//config:       Add support for renaming devices and creating symlinks.
//config:
//config:       For more information, please see docs/mdev.txt
//config:
//config:config FEATURE_MDEV_RENAME_REGEXP
//config:       bool "Support regular expressions substitutions when renaming device"
//config:       default y
//config:       depends on FEATURE_MDEV_RENAME
//config:       help
//config:       Add support for regular expressions substitutions when renaming
//config:       device.
//config:
//config:config FEATURE_MDEV_EXEC
//config:       bool "Support command execution at device addition/removal"
//config:       default y
//config:       depends on FEATURE_MDEV_CONF
//config:       help
//config:       This adds support for an optional field to /etc/mdev.conf for
//config:       executing commands when devices are created/removed.
//config:
//config:       For more information, please see docs/mdev.txt
//config:
//config:config FEATURE_MDEV_LOAD_FIRMWARE
//config:       bool "Support loading of firmware"
//config:       default y
//config:       depends on MDEV
//config:       help
//config:       Some devices need to load firmware before they can be usable.
//config:
//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]" 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"
//usage:        IF_FEATURE_MDEV_CONF(
//usage:       "\n"
//usage:       "It uses /etc/mdev.conf with lines\n"
//usage:       "        [-][ENV=regex;]...DEVNAME UID:GID PERM"
//usage:                        IF_FEATURE_MDEV_RENAME(" [>|=PATH]|[!]")
//usage:                        IF_FEATURE_MDEV_EXEC(" [@|$|*PROG]")
//usage:       "\n"
//usage:       "where DEVNAME is device name regex, @major,minor[-minor2], or\n"
//usage:       "environment variable regex. A common use of the latter is\n"
//usage:       "to load modules for hotplugged devices:\n"
//usage:       "        $MODALIAS=.* 0:0 660 @modprobe \"$MODALIAS\"\n"
//usage:        )
//usage:       "\n"
//usage:       "If /dev/mdev.seq file exists, mdev will wait for its value\n"
//usage:       "to match $SEQNUM variable. This prevents plug/unplug races.\n"
//usage:       "To activate this feature, create empty /dev/mdev.seq at boot.\n"
//usage:       "\n"
//usage:       "If /dev/mdev.log file exists, debug log will be appended to it."

#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
 * contains "4:0\n". Directory name is taken as device name, path component
 * directly after /sys/class/ as subsystem. In this example, "tty0" and "tty".
 * Then mdev creates the /dev/device_name node.
 * If /sys/class/.../dev file does not exist, mdev still may act
 * on this device: see "@|$|*command args..." parameter in config file.
 *
 * mdev w/o parameters is called as hotplug helper. It takes device
 * and subsystem names from $DEVPATH and $SUBSYSTEM, extracts
 * maj,min from "/sys/$DEVPATH/dev" and also examines
 * $ACTION ("add"/"delete") and $FIRMWARE.
 *
 * If action is "add", mdev creates /dev/device_name similarly to mdev -s.
 * (todo: explain "delete" and $FIRMWARE)
 *
 * If /etc/mdev.conf exists, it may modify /dev/device_name's properties.
 *
 * Leading minus in 1st field means "don't stop on this line", otherwise
 * search is stopped after the matching line is encountered.
 *
 * $envvar=regex format is useful for loading modules for hot-plugged devices
 * which do not have driver loaded yet. In this case /sys/class/.../dev
 * does not exist, but $MODALIAS is set to needed module's name
 * (actually, an alias to it) by kernel. This rule instructs mdev
 * to load the module and exit:
 *    $MODALIAS=.* 0:0 660 @modprobe "$MODALIAS"
 * The kernel will generate another hotplug event when /sys/class/.../dev
 * file appears.
 *
 * When line matches, the device node is created, chmod'ed and chown'ed,
 * moved to path, and if >path, a symlink to moved node is created,
 * all this if /sys/class/.../dev exists.
 *    Examples:
 *    =loop/      - moves to /dev/loop
 *    >disk/sda%1 - moves to /dev/disk/sdaN, makes /dev/sdaN a symlink
 *
 * Then "command args..." is executed (via sh -c 'command args...').
 * @:execute on creation, $:on deletion, *:on both.
 * This happens regardless of /sys/class/.../dev existence.
 */

/* Kernel's hotplug environment constantly changes.
 * Here are new cases I observed on 3.1.0:
 *
 * Case with $DEVNAME and $DEVICE, not just $DEVPATH:
 * ACTION=add
 * BUSNUM=001
 * DEVICE=/proc/bus/usb/001/003
 * DEVNAME=bus/usb/001/003
 * DEVNUM=003
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5
 * DEVTYPE=usb_device
 * MAJOR=189
 * MINOR=2
 * PRODUCT=18d1/4e12/227
 * SUBSYSTEM=usb
 * TYPE=0/0/0
 *
 * Case with $DEVICE, but no $DEVNAME - apparenty, usb iface notification?
 * "Please load me a module" thing?
 * ACTION=add
 * DEVICE=/proc/bus/usb/001/003
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0
 * DEVTYPE=usb_interface
 * INTERFACE=8/6/80
 * MODALIAS=usb:v18D1p4E12d0227dc00dsc00dp00ic08isc06ip50
 * PRODUCT=18d1/4e12/227
 * SUBSYSTEM=usb
 * TYPE=0/0/0
 *
 * ACTION=add
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5
 * DEVTYPE=scsi_host
 * SUBSYSTEM=scsi
 *
 * ACTION=add
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5/scsi_host/host5
 * SUBSYSTEM=scsi_host
 *
 * ACTION=add
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5/target5:0:0
 * DEVTYPE=scsi_target
 * SUBSYSTEM=scsi
 *
 * Case with strange $MODALIAS:
 * ACTION=add
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5/target5:0:0/5:0:0:0
 * DEVTYPE=scsi_device
 * MODALIAS=scsi:t-0x00
 * SUBSYSTEM=scsi
 *
 * ACTION=add
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5/target5:0:0/5:0:0:0/scsi_disk/5:0:0:0
 * SUBSYSTEM=scsi_disk
 *
 * ACTION=add
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5/target5:0:0/5:0:0:0/scsi_device/5:0:0:0
 * SUBSYSTEM=scsi_device
 *
 * Case with explicit $MAJOR/$MINOR (no need to read /sys/$DEVPATH/dev?):
 * ACTION=add
 * DEVNAME=bsg/5:0:0:0
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5/target5:0:0/5:0:0:0/bsg/5:0:0:0
 * MAJOR=253
 * MINOR=1
 * SUBSYSTEM=bsg
 *
 * ACTION=add
 * DEVPATH=/devices/virtual/bdi/8:16
 * SUBSYSTEM=bdi
 *
 * ACTION=add
 * DEVNAME=sdb
 * DEVPATH=/block/sdb
 * DEVTYPE=disk
 * MAJOR=8
 * MINOR=16
 * SUBSYSTEM=block
 *
 * Case with ACTION=change:
 * ACTION=change
 * DEVNAME=sdb
 * DEVPATH=/block/sdb
 * DEVTYPE=disk
 * DISK_MEDIA_CHANGE=1
 * MAJOR=8
 * MINOR=16
 * SUBSYSTEM=block
 */

#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


#ifndef SO_RCVBUFFORCE
#define SO_RCVBUFFORCE 33
#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;
        mode_t mode;
        int maj, min0, min1;
        struct bb_uidgid_t ugid;
        char *envvar;
        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;
        struct rule **rule_vec;
        unsigned rule_idx;
#endif
        struct rule cur_rule;
        char timestr[sizeof("HH:MM:SS.123456")];
} FIX_ALIASING;
#define G (*(struct globals*)bb_common_bufsiz1)
#define INIT_G() do { \
        setup_common_bufsiz(); \
        IF_NOT_FEATURE_MDEV_CONF(G.cur_rule.maj = -1;) \
        IF_NOT_FEATURE_MDEV_CONF(G.cur_rule.mode = 0660;) \
} while (0)


/* Prevent infinite loops in /sys symlinks */
#define MAX_SYSFS_DEPTH 3

/* We use additional bytes in make_device() */
#define SCRATCH_SIZE 128

#if ENABLE_FEATURE_MDEV_CONF

static void make_default_cur_rule(void)
{
        memset(&G.cur_rule, 0, sizeof(G.cur_rule));
        G.cur_rule.maj = -1; /* "not a @major,minor rule" */
        G.cur_rule.mode = 0660;
}

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);
        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 */
        while (1) {
                char *tokens[4];
                char *val;

                /* No PARSE_EOL_COMMENTS, because command may contain '#' chars */
                if (!config_read(G.parser, tokens, 4, 3, "# \t", PARSE_NORMAL & ~PARSE_EOL_COMMENTS))
                        break;

                /* Fields: [-]regex uid:gid mode [alias] [cmd] */
                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:
                         * "/sys/class/usb/lp0" and
                         * "/sys/class/printer/lp0")
                         */
                        int sc = sscanf(val, "@%u,%u-%u", &G.cur_rule.maj, &G.cur_rule.min0, &G.cur_rule.min1);
                        if (sc < 2 || G.cur_rule.maj < 0) {
                                bb_error_msg("bad @maj,min on line %d", G.parser->lineno);
                                goto next_rule;
                        }
                        if (sc == 2)
                                G.cur_rule.min1 = G.cur_rule.min0;
                } else {
                        char *eq = strchr(val, '=');
                        if (val[0] == '$') {
                                /* $ENVVAR=regex ... */
                                val++;
                                if (!eq) {
                                        bb_error_msg("bad $envvar=regex on line %d", G.parser->lineno);
                                        goto next_rule;
                                }
                                G.cur_rule.envvar = xstrndup(val, eq - val);
                                val = eq + 1;
                        }
                        xregcomp(&G.cur_rule.match, val, REG_EXTENDED);
                        G.cur_rule.regex_compiled = 1;
                }

                /* 2nd field: uid:gid - device ownership */
                if (get_uidgid(&G.cur_rule.ugid, tokens[1]) == 0) {
                        bb_error_msg("unknown user/group '%s' on line %d", tokens[1], G.parser->lineno);
                        goto next_rule;
                }

                /* 3rd field: mode - device permissions */
                G.cur_rule.mode = bb_parse_mode(tokens[2], G.cur_rule.mode);

                /* 4th field (opt): ">|=alias" or "!" to not create the node */
                val = tokens[3];
                if (ENABLE_FEATURE_MDEV_RENAME && val && strchr(">=!", val[0])) {
                        char *s = skip_non_whitespace(val);
                        G.cur_rule.ren_mov = xstrndup(val, s - val);
                        val = skip_whitespace(s);
                }

                if (ENABLE_FEATURE_MDEV_EXEC && val && val[0]) {
                        const char *s = "$@*";
                        const char *s2 = strchr(s, val[0]);
                        if (!s2) {
                                bb_error_msg("bad line %u", G.parser->lineno);
                                goto next_rule;
                        }
                        IF_FEATURE_MDEV_EXEC(G.cur_rule.r_cmd = xstrdup(val);)
                }

                return;
 next_rule:
                clean_up_cur_rule();
        } /* while (config_read) */

        dbg3("config_close(G.parser)");
        config_close(G.parser);
        G.parser = NULL;

        return;
}

/* If mdev -s, we remember rules in G.rule_vec[].
 * Otherwise, there is no point in doing it, and we just
 * save only one parsed rule in G.cur_rule.
 */
static const struct rule *next_rule(void)
{
        struct rule *rule;

        /* Open conf file if we didn't do it yet */
        if (!G.parser && G.filename) {
                dbg3("config_open('%s')", G.filename);
                G.parser = config_open2(G.filename, fopen_for_read);
                G.filename = NULL;
        }

        if (G.rule_vec) {
                /* mdev -s */
                /* Do we have rule parsed already? */
                if (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();
        } else {
                /* not mdev -s */
                clean_up_cur_rule();
        }

        /* Parse one more rule if file isn't fully read */
        rule = &G.cur_rule;
        if (G.parser) {
                parse_next_rule();
                if (G.rule_vec) { /* mdev -s */
                        rule = xmemdup(&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;
                        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
 */
static char *build_alias(char *alias, const char *device_name)
{
        char *dest;

        /* ">bar/": rename to bar/device_name */
        /* ">bar[/]baz": rename to bar[/]baz */
        dest = strrchr(alias, '/');
        if (dest) { /* ">bar/[baz]" ? */
                *dest = '\0'; /* mkdir bar */
                mkdir_recursive(alias);
                *dest = '/';
                if (dest[1] == '\0') { /* ">bar/" => ">bar/device_name" */
                        dest = alias;
                        alias = concat_path_file(alias, device_name);
                        free(dest);
                }
        }

        return alias;
}

/* 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 it (IOW: to restore NUL if needed).
 * NB2: "mdev -s" may call us many times, do not leak memory/fds!
 *
 * device_name = $DEVNAME (may be NULL)
 * path        = /sys/$DEVPATH
 */
static void make_device(char *device_name, char *path, int operation)
{
        int major, minor, type, len;
        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
         * because sscanf() will stop at the first nondigit, which \n is.
         * We also depend on path having writeable space after it.
         */
        major = -1;
        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(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 */
        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.
         */
        type = S_IFCHR;
        if (strstr(path, "/block/") || (G.subsystem && is_prefixed_with(G.subsystem, "block")))
                type = S_IFBLK;

#if ENABLE_FEATURE_MDEV_CONF
        G.rule_idx = 0; /* restart from the beginning (think mdev -s) */
#endif
        for (;;) {
                const char *str_to_match;
                regmatch_t off[1 + 9 * ENABLE_FEATURE_MDEV_RENAME_REGEXP];
                char *command;
                char *alias;
                char aliaslink = aliaslink; /* for compiler */
                char *node_name;
                const struct rule *rule;

                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;
                        if (minor < rule->min0 || minor > rule->min1)
                                continue;
                        memset(off, 0, sizeof(off));
                        goto rule_matches;
                }
                if (rule->envvar) { /* $envvar=regex rule */
                        str_to_match = getenv(rule->envvar);
                        dbg3("getenv('%s'):'%s'", rule->envvar, str_to_match);
                        if (!str_to_match)
                                continue;
                }
                /* else: str_to_match = device_name */

                if (rule->regex_compiled) {
                        int regex_match = regexec(&rule->match, str_to_match, ARRAY_SIZE(off), off, 0);
                        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;
                        //      bb_error_msg("match %d: '%.*s'\n", i,
                        //              (int)(off[i].rm_eo - off[i].rm_so),
                        //              device_name + off[i].rm_so);
                        //}

                        if (regex_match != 0
                        /* regexec returns whole pattern as "range" 0 */
                         || off[0].rm_so != 0
                         || (int)off[0].rm_eo != (int)strlen(str_to_match)
                        ) {
                                continue; /* this rule doesn't match */
                        }
                }
                /* else: it's final implicit "match-all" rule */
 rule_matches:
                dbg2("rule matched, line %d", G.parser ? G.parser->lineno : -1);
#endif
                /* Build alias name */
                alias = NULL;
                if (ENABLE_FEATURE_MDEV_RENAME && rule->ren_mov) {
                        aliaslink = rule->ren_mov[0];
                        if (aliaslink == '!') {
                                /* "!": suppress node creation/deletion */
                                major = -2;
                        }
                        else if (aliaslink == '>' || aliaslink == '=') {
                                if (ENABLE_FEATURE_MDEV_RENAME_REGEXP) {
                                        char *s;
                                        char *p;
                                        unsigned n;

                                        /* substitute %1..9 with off[1..9], if any */
                                        n = 0;
                                        s = rule->ren_mov;
                                        while (*s)
                                                if (*s++ == '%')
                                                        n++;

                                        p = alias = xzalloc(strlen(rule->ren_mov) + n * strlen(str_to_match));
                                        s = rule->ren_mov + 1;
                                        while (*s) {
                                                *p = *s;
                                                if ('%' == *s) {
                                                        unsigned i = (s[1] - '0');
                                                        if (i <= 9 && off[i].rm_so >= 0) {
                                                                n = off[i].rm_eo - off[i].rm_so;
                                                                strncpy(p, str_to_match + off[i].rm_so, n);
                                                                p += n - 1;
                                                                s++;
                                                        }
                                                }
                                                p++;
                                                s++;
                                        }
                                } else {
                                        alias = xstrdup(rule->ren_mov + 1);
                                }
                        }
                }
                dbg3("alias:'%s'", alias);

                command = NULL;
                IF_FEATURE_MDEV_EXEC(command = rule->r_cmd;)
                if (command) {
                        /* Are we running this command now?
                         * Run @cmd on create, $cmd on delete, *cmd on any
                         */
                        if ((command[0] == '@' && operation == OP_add)
                         || (command[0] == '$' && operation == OP_remove)
                         || (command[0] == '*')
                        ) {
                                command++;
                        } else {
                                command = NULL;
                        }
                }
                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);
                        dbg3("alias2:'%s'", alias);
                }

                if (operation == OP_add && major >= 0) {
                        char *slash = strrchr(node_name, '/');
                        if (slash) {
                                *slash = '\0';
                                mkdir_recursive(node_name);
                                *slash = '/';
                        }
                        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 (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?
                                        dbg1("symlink: %s", device_name);
                                        symlink(node_name, device_name);
                                }
                        }
                }

                if (ENABLE_FEATURE_MDEV_EXEC && command) {
                        /* setenv will leak memory, use putenv/unsetenv/free */
                        char *s = xasprintf("%s=%s", "MDEV", node_name);
                        putenv(s);
                        dbg1("running: %s", command);
                        if (system(command) == -1)
                                bb_perror_msg("can't run '%s'", command);
                        bb_unsetenv_and_free(s);
                }

                if (operation == OP_remove && major >= -1) {
                        if (ENABLE_FEATURE_MDEV_RENAME && alias) {
                                if (aliaslink == '>') {
                                        dbg1("unlink: %s", device_name);
                                        unlink(device_name);
                                }
                        }
                        dbg1("unlink: %s", node_name);
                        unlink(node_name);
                }

                if (ENABLE_FEATURE_MDEV_RENAME)
                        free(alias);

                /* We found matching line.
                 * Stop unless it was prefixed with '-'
                 */
                if (!ENABLE_FEATURE_MDEV_CONF || !rule->keep_matching)
                        break;
        } /* for (;;) */
}

static ssize_t readlink2(char *buf, size_t bufsize)
{
        // Grr... gcc 8.1.1:
        // "passing argument 2 to restrict-qualified parameter aliases with argument 1"
        // dance around that...
        char *obuf FIX_ALIASING;
        obuf = buf;
        return readlink(buf, obuf, bufsize);
}

/* File callback for /sys/ traversal.
 * We act only on "/sys/.../dev" (pseudo)file
 */
static int FAST_FUNC fileAction(const char *fileName,
                struct stat *statbuf UNUSED_PARAM,
                void *userData,
                int depth UNUSED_PARAM)
{
        size_t len = strlen(fileName) - 4; /* can't underflow */
        char *path = userData;  /* char array[PATH_MAX + SCRATCH_SIZE] */
        char subsys[PATH_MAX];
        int res;

        /* Is it a ".../dev" file? (len check is for paranoid reasons) */
        if (strcmp(fileName + len, "/dev") != 0 || len >= PATH_MAX - 32)
                return FALSE; /* not .../dev */

        strcpy(path, fileName);
        path[len] = '\0';

        /* Read ".../subsystem" symlink in the same directory where ".../dev" is */
        strcpy(subsys, path);
        strcpy(subsys + len, "/subsystem");
        res = readlink2(subsys, sizeof(subsys)-1);
        if (res > 0) {
                subsys[res] = '\0';
                free(G.subsystem);
                if (G.subsys_env) {
                        bb_unsetenv_and_free(G.subsys_env);
                        G.subsys_env = NULL;
                }
                /* Set G.subsystem and $SUBSYSTEM from symlink's last component */
                G.subsystem = strrchr(subsys, '/');
                if (G.subsystem) {
                        G.subsystem = xstrdup(G.subsystem + 1);
                        G.subsys_env = xasprintf("%s=%s", "SUBSYSTEM", G.subsystem);
                        putenv(G.subsys_env);
                }
        }

        make_device(/*DEVNAME:*/ NULL, path, OP_add);

        return TRUE;
}

/* Directory callback for /sys/ traversal */
static int FAST_FUNC dirAction(const char *fileName UNUSED_PARAM,
                struct stat *statbuf UNUSED_PARAM,
                void *userData UNUSED_PARAM,
                int depth)
{
        return (depth >= MAX_SYSFS_DEPTH ? SKIP : TRUE);
}

/* For the full gory details, see linux/Documentation/firmware_class/README
 *
 * Firmware loading works like this:
 * - kernel sets FIRMWARE env var
 * - userspace checks /lib/firmware/$FIRMWARE
 * - userspace waits for /sys/$DEVPATH/loading to appear
 * - userspace writes "1" to /sys/$DEVPATH/loading
 * - userspace copies /lib/firmware/$FIRMWARE into /sys/$DEVPATH/data
 * - userspace writes "0" (worked) or "-1" (failed) to /sys/$DEVPATH/loading
 * - kernel loads firmware into device
 */
static void load_firmware(const char *firmware, const char *sysfs_path)
{
        int cnt;
        int firmware_fd, loading_fd;

        /* check for /lib/firmware/$FIRMWARE */
        firmware_fd = -1;
        if (chdir("/lib/firmware") == 0)
                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 >= 0)
                        goto loading;
                sleep(1);
        }
        goto out;

 loading:
        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"
         * 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);
        }
}

static char *curtime(void)
{
        struct timeval tv;
        gettimeofday(&tv, NULL);
        sprintf(
                strftime_HHMMSS(G.timestr, sizeof(G.timestr), &tv.tv_sec),
                ".%06u",
                (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(unsigned expected_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(long)*3 + 2];
                unsigned seqbufnum;

                if (seq_fd < 0) {
                        seq_fd = open("mdev.seq", O_RDWR);
                        if (seq_fd < 0)
                                break;
                        close_on_exec_on(seq_fd);
                }
                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' || seqbuf[0] == '\0') {
                        /* seed file: write out seq ASAP */
                        xwrite_str(seq_fd, utoa(expected_seq));
                        xlseek(seq_fd, 0, SEEK_SET);
                        dbg2("first seq written");
                        break;
                }
                seqbufnum = atoll(seqbuf);
                if (seqbufnum == expected_seq) {
                        /* correct idx */
                        break;
                }
                if (seqbufnum > expected_seq) {
                        /* a later mdev runs already (this was seen by users to happen) */
                        /* do not overwrite seqfile on exit */
                        close(seq_fd);
                        seq_fd = -1;
                        break;
                }
                if (do_once) {
                        dbg2("%s mdev.seq='%s', need '%u'", curtime(), seqbuf, expected_seq);
                        do_once = 0;
                }
                if (sigtimedwait(&set_CHLD, NULL, &ts) >= 0) {
                        dbg3("woken up");
                        continue; /* don't decrement timeout! */
                }
                if (--timeout == 0) {
                        dbg1("%s mdev.seq='%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);
                }
        }
}

static void process_action(char *temp, unsigned my_pid)
{
        char *fw;
        char *seq;
        char *action;
        char *env_devname;
        char *env_devpath;
        unsigned seqnum = seqnum; /* for compiler */
        int seq_fd;
        smalluint op;

        /* Hotplug:
         * env ACTION=... DEVPATH=... SUBSYSTEM=... [SEQNUM=...] mdev
         * ACTION can be "add", "remove", "change"
         * DEVPATH is like "/block/sda" or "/class/input/mice"
         */
        env_devname = getenv("DEVNAME"); /* can be NULL */
        G.subsystem = getenv("SUBSYSTEM");
        action = getenv("ACTION");
        env_devpath = getenv("DEVPATH");
        if (!action || !env_devpath /*|| !G.subsystem*/)
                bb_show_usage();
        fw = getenv("FIRMWARE");
        seq = getenv("SEQNUM");
        op = index_in_strings(keywords, action);

        if (my_pid)
                open_mdev_log(seq, my_pid);

        seq_fd = -1;
        if (my_pid && seq) {
                seqnum = atoll(seq);
                seq_fd = wait_for_seqfile(seqnum);
        }

        dbg1("%s "
                "ACTION:%s SEQNUM:%s SUBSYSTEM:%s DEVNAME:%s DEVPATH:%s"
                "%s%s",
                curtime(),
                action, seq, G.subsystem, env_devname, env_devpath,
                fw ? " FW:" : "", fw ? fw : ""
        );

        snprintf(temp, PATH_MAX, "/sys%s", env_devpath);
        if (op == OP_remove) {
                /* Ignoring "remove firmware". It was reported
                 * to happen and to cause erroneous deletion
                 * of device nodes. */
                if (!fw)
                        make_device(env_devname, temp, op);
        }
        else {
                make_device(env_devname, temp, op);
                if (ENABLE_FEATURE_MDEV_LOAD_FIRMWARE) {
                        if (op == OP_add && fw)
                                load_firmware(fw, temp);
                }
        }

        if (seq_fd >= 0) {
                xwrite_str(seq_fd, utoa(seqnum + 1));
                signal_mdevs(my_pid);
        }
}

static void initial_scan(char *temp)
{
        struct stat st;

        xstat("/", &st);
        G.root_major = major(st.st_dev);
        G.root_minor = minor(st.st_dev);

        putenv((char*)"ACTION=add");

        /* Create all devices from /sys/dev hierarchy */
        recursive_action("/sys/dev",
                         ACTION_RECURSE | ACTION_FOLLOWLINKS,
                         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();

        /* We can be called as hotplug helper */
        /* Kernel cannot provide suitable stdio fds for us, do it ourself */
        bb_sanitize_stdio();

        /* Force the configuration file settings exactly */
        umask(0);

        xchdir("/dev");

        opt = getopt32(argv, "s" IF_FEATURE_MDEV_DAEMON("df"));

#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.
                 */
                int fd;

                /* Subscribe for UEVENT kernel messages */
                /* 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 >"{}"' ';'
                 */
                fd = create_and_bind_to_netlink(NETLINK_KOBJECT_UEVENT, 1 << 0, 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());

                dbg1("%s exiting", curtime());
        }

        if (ENABLE_FEATURE_CLEAN_UP)
                RELEASE_CONFIG_BUFFER(temp);

        return EXIT_SUCCESS;
}