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List: busybox
Subject: Re: Can mdev replace udev in an ordinary linux distro?
From: Souf <souf_oued () yahoo ! fr>
Date: 2011-09-22 20:10:29
Message-ID: 4E7B9635.8030700 () yahoo ! fr
[Download RAW message or body]
Hi all,
A few years ago, I have participated in this discussion.
I think mdev suffers from a major design flaw. Instead of dev, mdev
should use uevent, for example:
/sys/class/input/event1/uevent contains :
MAJOR=13
MINOR=65
DEVNAME=input/event1
We have MAJOR, MINOR and DEVNAME about our device
DEVNAME = the path and name of the device under /dev, event1 is
automatically created in this way:
/dev/input/event1 and we are not obliged to specify the path in mdev.conf
In hotplug, the same informations are exported as environment variables
MAJOR
MINOR
DEVNAME
DEVMODE (for: null, zero, full, urandom, random, tty and ptmx)
SUBSYSTEM (mdev is called with argv[1] = SUBSYSTEM)
ACTION
DEVPATH
FIRMWARE
SEQNUM
I use this structure:
struct globals {
int major;
int minor;
mode_t devmode;
char *devname;
char *devpath;
char *subsystem;
} FIX_ALIASING;
#define G (*(struct globals*)&bb_common_bufsiz1)
#define k_major (G.major )
#define k_minor (G.minor )
#define k_devmode (G.devmode )
#define k_devname (G.devname )
#define k_devpath (G.devpath )
#define k_subsystem (G.subsystem )
#define INIT_G() do { \
k_major = -1; \
k_minor = -1; \
k_devmode = 0660; \
k_devname = NULL; \
k_devpath = NULL; \
k_subsystem = NULL; \
} while (0)
Attached : mdev.c
["mdev.c" (text/plain)]
/* 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.
*/
//usage:#define mdev_trivial_usage
//usage: "[-s]"
//usage:#define mdev_full_usage "\n\n"
//usage: " -s Scan /sys and populate /dev during system boot\n"
//usage: "\n"
//usage: "It can be run by kernel as a hotplug helper. To activate it:\n"
//usage: " echo /sbin/mdev > /proc/sys/kernel/hotplug\n"
//usage: IF_FEATURE_MDEV_CONF(
//usage: "It uses /etc/mdev.conf with lines\n"
//usage: "[-]DEVNAME UID:GID PERM"
//usage: IF_FEATURE_MDEV_RENAME(" [>|=PATH]")
//usage: IF_FEATURE_MDEV_EXEC(" [@|$|*PROG]")
//usage: )
//usage:
//usage:#define mdev_notes_usage ""
//usage: IF_FEATURE_MDEV_CONFIG(
//usage: "The mdev config file contains lines that look like:\n"
//usage: " hd[a-z][0-9]* 0:3 660\n\n"
//usage: "That's device name (with regex match), uid:gid, and permissions.\n\n"
//usage: IF_FEATURE_MDEV_EXEC(
//usage: "Optionally, that can be followed (on the same line) by a special character\n"
//usage: "and a command line to run after creating/before deleting the corresponding\n"
//usage: "device(s). The environment variable $MDEV indicates the active device node\n"
//usage: "(which is useful if it's a regex match). For example:\n\n"
//usage: " hdc root:cdrom 660 *ln -s $MDEV cdrom\n\n"
//usage: "The special characters are @ (run after creating), $ (run before deleting),\n"
//usage: "and * (run both after creating and before deleting). The commands run in\n"
//usage: "the /dev directory, and use system() which calls /bin/sh.\n\n"
//usage: )
//usage: "Config file parsing stops on the first matching line. If no config\n"
//usage: "entry is matched, devices are created with default 0:0 660. (Make\n"
//usage: "the last line match .* to override this.)\n\n"
//usage: )
#include "libbb.h"
#include "xregex.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 $FIRMWARE)
*
* If /etc/mdev.conf exists, it may modify /dev/device_name's properties.
* /etc/mdev.conf file format:
*
* [-][subsystem/]device user:grp mode [>|=path] [@|$|*command args...]
* [-]@maj,min[-min2] user:grp mode [>|=path] [@|$|*command args...]
* [-]$envvar=val user:grp mode [>|=path] [@|$|*command args...]
*
* Leading minus in 1st field means "don't stop on this line", otherwise
* search is stopped after the matching line is encountered.
*
* The device name or "subsystem/device" combo is matched against 1st field
* (which is a regex), or maj,min is matched against 1st field,
* or specified environment variable (as regex) is matched against 1st field.
*
* $envvar=val 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.
*/
struct globals {
int major;
int minor;
mode_t devmode;
char *devname;
char *devpath;
char *subsystem;
} FIX_ALIASING;
#define G (*(struct globals*)&bb_common_bufsiz1)
#define k_major (G.major )
#define k_minor (G.minor )
#define k_devmode (G.devmode )
#define k_devname (G.devname )
#define k_devpath (G.devpath )
#define k_subsystem (G.subsystem )
#define INIT_G() do { \
k_major = -1; \
k_minor = -1; \
k_devmode = 0660; \
k_devname = NULL; \
k_devpath = NULL; \
k_subsystem = NULL; \
} while (0)
/* Prevent infinite loops in /sys symlinks */
#define MAX_SYSFS_DEPTH 3
/* We use additional 64+ bytes in make_device() */
#define SCRATCH_SIZE 80
/* 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)
* path string.
* NB2: "mdev -s" may call us many times, do not leak memory/fds!
*/
static void make_device(int delete)
{
char *device_name;
char *device_path = NULL;
int type;
parser_t *parser;
/* 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.
*/
/* Determine device name, type, major and minor */
device_name = (char *)bb_basename(k_devname);
if (strcmp(device_name, k_devname) != 0) {
device_path = xstrndup(k_devname, strlen(k_devname) - strlen(device_name));
}
/* 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 (k_subsystem && strcmp(k_subsystem, "block") == 0) {
type = S_IFBLK;
}
/* If we have config file, look up user settings */
if (ENABLE_FEATURE_MDEV_CONF)
parser = config_open2("/etc/mdev.conf", fopen_for_read);
do {
int keep_matching;
struct bb_uidgid_t ugid;
char *tokens[4];
char *command = NULL;
char *alias = NULL;
char aliaslink = aliaslink; /* for compiler */
/* Defaults in case we won't match any line */
ugid.uid = ugid.gid = 0;
keep_matching = 0;
if (ENABLE_FEATURE_MDEV_CONF
&& config_read(parser, tokens, 4, 3, "# \t", PARSE_NORMAL)
) {
char *val;
char *str_to_match;
regmatch_t off[1 + 9 * ENABLE_FEATURE_MDEV_RENAME_REGEXP];
val = tokens[0];
keep_matching = ('-' == val[0]);
val += keep_matching; /* swallow leading dash */
/* Match against either "subsystem/device_name"
* or "device_name" alone */
str_to_match = strchr(val, '/') ? k_devname : device_name;
/* Fields: regex uid:gid mode [alias] [cmd] */
if (val[0] == '$') {
/* regex to match an environment variable */
char *eq = strchr(++val, '=');
if (!eq)
continue;
*eq = '\0';
str_to_match = getenv(val);
if (!str_to_match)
continue;
str_to_match -= strlen(val) + 1;
*eq = '=';
}
/* else: regex to match [subsystem/]device_name */
{
regex_t match;
int result;
xregcomp(&match, val, REG_EXTENDED);
result = regexec(&match, str_to_match, ARRAY_SIZE(off), off, 0);
regfree(&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 no match, skip rest of line */
/* (regexec returns whole pattern as "range" 0) */
if (result
|| off[0].rm_so
|| ((int)off[0].rm_eo != (int)strlen(str_to_match))
) {
continue; /* this line doesn't match */
}
}
/* This line matches. Stop parsing after parsing
* the rest the line unless keep_matching == 1 */
/* 2nd field: uid:gid - device ownership */
if (get_uidgid(&ugid, tokens[1], 1) == 0)
bb_error_msg("unknown user/group %s on line %d", tokens[1], parser->lineno);
/* 3rd field: mode - device permissions */
if (k_devmode == 0660) {
bb_parse_mode(tokens[2], &k_devmode);
}
val = tokens[3];
/* 4th field (opt): ">|=alias" or "!" to not create the node */
if (ENABLE_FEATURE_MDEV_RENAME && val) {
char *a, *s, *st;
a = val;
s = strchrnul(val, ' ');
st = strchrnul(val, '\t');
if (st < s)
s = st;
st = (s[0] && s[1]) ? s+1 : NULL;
aliaslink = a[0];
if (aliaslink == '!' && s == a+1) {
val = st;
/* "!": suppress node creation/deletion */
k_major = -1;
}
else if (aliaslink == '>' || aliaslink == '=') {
val = st;
s[0] = '\0';
if (ENABLE_FEATURE_MDEV_RENAME_REGEXP) {
char *p;
unsigned i, n;
/* substitute %1..9 with off[1..9], if any */
n = 0;
s = a;
while (*s)
if (*s++ == '%')
n++;
p = alias = xzalloc(strlen(a) + n * strlen(str_to_match));
s = a + 1;
while (*s) {
*p = *s;
if ('%' == *s) {
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(a + 1);
}
}
}
if (ENABLE_FEATURE_MDEV_EXEC && val) {
const char *s = "$@*";
const char *s2 = strchr(s, val[0]);
if (!s2) {
bb_error_msg("bad line %u", parser->lineno);
if (ENABLE_FEATURE_MDEV_RENAME)
free(alias);
continue;
}
/* Are we running this command now?
* Run $cmd on delete, @cmd on create, *cmd on both
*/
if (s2 - s != delete) {
/* We are here if: '*',
* or: '@' and delete = 0,
* or: '$' and delete = 1
*/
command = xstrdup(val + 1);
}
}
}
/* End of field parsing */
/* "Execute" the line we found */
{
const char *node_name;
if (device_path) {
node_name = k_devname;
bb_make_directory(device_path, 0755, FILEUTILS_RECUR);
free(device_path);
} else {
node_name = device_name;
}
if (!delete && k_major >= 0) {
if (mknod(node_name, k_devmode | type, makedev(k_major, k_minor)) && errno != EEXIST)
bb_perror_msg("can't create '%s'", node_name);
if (ENABLE_FEATURE_MDEV_CONF) {
chmod(node_name, k_devmode);
chown(node_name, ugid.uid, ugid.gid);
}
if (ENABLE_FEATURE_MDEV_RENAME && alias) {
if (aliaslink == '>')
symlink(node_name, alias);
}
}
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", k_subsystem);
putenv(s);
putenv(s1);
if (system(command) == -1)
bb_perror_msg("can't run '%s'", command);
bb_unsetenv_and_free(s1);
bb_unsetenv_and_free(s);
free(command);
}
if (delete && k_major >= 0) {
if (ENABLE_FEATURE_MDEV_RENAME && alias) {
if (aliaslink == '>')
unlink(device_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 && !keep_matching)
break;
/* end of "while line is read from /etc/mdev.conf" */
} while (ENABLE_FEATURE_MDEV_CONF);
if (ENABLE_FEATURE_MDEV_CONF)
config_close(parser);
}
/* File callback for /sys/ traversal */
static int FAST_FUNC fileAction(const char *fileName,
struct stat *statbuf UNUSED_PARAM,
void *userData UNUSED_PARAM,
int depth UNUSED_PARAM)
{
parser_t *parser;
char *tokens[2];
if (strcmp(bb_basename(fileName), "uevent") != 0)
return FALSE;
parser = config_open2(fileName, fopen_for_read);
while (config_read(parser, tokens, 2, 2, "\\/=", PARSE_NORMAL)) {
if (parser->lineno == 1) {
if (strcmp(tokens[0], "MAJOR") == 0) {
k_major = xstrtou(tokens[1], 10);
continue;
} else {
break;
}
}
if (strcmp(tokens[0], "MINOR") == 0) {
k_minor = xstrtou(tokens[1], 10);
continue;
}
if (strcmp(tokens[0], "DEVNAME") == 0) {
k_devname = xstrdup(tokens[1]);
continue;
}
if (strcmp(tokens[0], "DEVMODE") == 0) {
k_devmode = xstrtou(tokens[1], 8);
} else {
k_devmode = 0660;
}
}
config_close(parser);
make_device(/*delete:*/ 0);
return TRUE;
}
/* Directory callback for /sys/ traversal */
static int FAST_FUNC dirAction(const char *fileName,
struct stat *statbuf UNUSED_PARAM,
void *userData UNUSED_PARAM,
int depth)
{
/* Extract device subsystem -- the name of the directory
* pointed by subsystem symlink */
if (strcmp(bb_basename(fileName), "subsystem") == 0 && is_directory(fileName, 0, NULL) == 0) {
k_subsystem = (char *)bb_basename(xmalloc_realpath(fileName));
}
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)
{
int cnt;
int firmware_fd, loading_fd, data_fd;
RESERVE_CONFIG_BUFFER(sysfs_path, PATH_MAX + SCRATCH_SIZE);
snprintf(sysfs_path, PATH_MAX, "/sys%s", k_devpath);
/* check for /lib/firmware/$FIRMWARE */
xchdir("/lib/firmware");
firmware_fd = xopen(firmware, O_RDONLY);
/* in case we goto out ... */
data_fd = -1;
/* check for /sys/$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)
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);
/* tell kernel result by "echo [0|-1] > /sys/$DEVPATH/loading" */
if (cnt > 0)
full_write(loading_fd, "0", 1);
else
full_write(loading_fd, "-1", 2);
out:
if (ENABLE_FEATURE_CLEAN_UP) {
RELEASE_CONFIG_BUFFER(sysfs_path);
close(firmware_fd);
close(loading_fd);
close(data_fd);
}
}
int mdev_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int mdev_main(int argc UNUSED_PARAM, char **argv)
{
INIT_G();
single_argv(argv);
/* 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");
if (strcmp(argv[1], "-s") == 0) {
/* Scan:
* mdev -s
*/
char *root_dev = find_block_device("/");
if (root_dev)
symlink(bb_basename(root_dev), "root");
if (access("/sys/dev", F_OK) == 0) {
recursive_action("/sys/dev",
ACTION_RECURSE | ACTION_FOLLOWLINKS,
fileAction, dirAction, NULL, 0);
} else {
/* ACTION_FOLLOWLINKS is needed since in newer kernels
* /sys/block/loop* (for example) are symlinks to dirs,
* not real directories.
* (kernel's CONFIG_SYSFS_DEPRECATED makes them real dirs,
* but we can't enforce that on users)
*/
if (access("/sys/class/block", F_OK) != 0) {
/* Scan obsolete /sys/block only if /sys/class/block
* doesn't exist. Otherwise we'll have dupes.
* Also, do not complain if it doesn't exist.
* Some people configure kernel to have no blockdevs.
*/
recursive_action("/sys/block",
ACTION_RECURSE | ACTION_FOLLOWLINKS | ACTION_QUIET,
fileAction, dirAction, NULL, 0);
}
recursive_action("/sys/class",
ACTION_RECURSE | ACTION_FOLLOWLINKS,
fileAction, dirAction, NULL, 0);
}
} else {
char *fw;
char *seq;
char *action;
char *m;
// static const char keywords[] ALIGN1 = "remove\0add\0change\0";
static const char keywords[] ALIGN1 = "remove\0add\0";
enum { OP_remove = 0, OP_add };
// enum { OP_remove = 0, OP_add, OP_change };
smalluint op;
/* Hotplug:
* env ACTION=... DEVPATH=... SUBSYSTEM=... [SEQNUM=...] mdev
* DEVNAME is like snd/timer
* ACTION can be "add" or "remove"
* DEVPATH is like "/block/sda" or "/class/input/mice"
*/
// k_subsystem = getenv("SUBSYSTEM");
k_subsystem = argv[1];
action = getenv("ACTION");
k_devpath = getenv("DEVPATH");
k_devname = getenv("DEVNAME");
if (!k_subsystem || !action || !k_devname)
xfunc_die();
m = getenv("MAJOR");
if (m)
k_major = xstrtou(m, 10);
m = getenv("MINOR");
if (m)
k_minor = xstrtou(m, 10);
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);
}
if (op == OP_remove) {
/* Ignoring "remove firmware". It was reported
* to happen and to cause erroneous deletion
* of device nodes. */
if (!fw)
make_device(/*delete:*/ 1);
}
else if (op == OP_add) {
make_device(/*delete:*/ 0);
if (ENABLE_FEATURE_MDEV_LOAD_FIRMWARE) {
if (fw) {
load_firmware(fw);
}
}
}
if (seq) {
xopen_xwrite_close("mdev.seq", utoa(xatou(seq) + 1));
}
}
return EXIT_SUCCESS;
}
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