Upgrade mdev to allow commands to be run on create/delete.

Both Jason Schoon and Giuseppe Ciotta deserve credit for this, I used elements
of both.  It's been upgraded so that you can specify that a given command
should run at create, at delete, or at both using different special characters
(@, $, and * respectively).  It uses the system() method of running command
lines which means you can use environment variables on the command line (it
sets $MDEV to the name of the current device being created/deleted, which is
useful if you matched it via regex), and the documentation warns that you need
a /bin/sh to make that work, so you probably want to pick a default shell.

3 files changed, 130 insertions, 105 deletions

diff --git a/include/usage.h b/include/usage.h
index 8defbd1..712eede 100644
--- a/include/usage.h
+++ b/include/usage.h
@@ -1799,19 +1799,25 @@ USE_FEATURE_DATE_ISOFMT( \
 	"\t-s\tScan /sys and populate /dev during system boot\n\n" \
 	"Called with no options (via hotplug) it uses environment variables\n" \
 	"to determine which device to add/remove."
-#ifdef CONFIG_FEATURE_MDEV_CONFIG
-#define mdev_notes_usage \
+#define mdev_notes_usage "" \
+USE_FEATURE_MDEV_CONFIG( \
 	"The mdev config file contains lines that look like:\n" \
 	"  hd[a-z][0-9]* 0:3 660\n\n" \
 	"That's device name (with regex match), uid:gid, and permissions.\n\n" \
-	"Optionally, that can be followed (on the same line) by an asterisk\n" \
-	"and a command line to run after creating the corresponding device(s),\n"\
-	"ala:\n\n" \
-	"  hdc root:cdrom 660  *ln -s hdc cdrom\n\n" \
+	USE_FEATURE_MDEV_EXEC( \
+		"Optionally, that can be followed (on the same line) by a special character\n" \
+		"and a command line to run after creating/before deleting the corresponding\n" \
+		"device(s).  The environment variable $MDEV indicates the active device node\n" \
+		"(which is useful if it's a regex match).  For example:\n\n" \
+		"  hdc root:cdrom 660  *ln -s $MDEV cdrom\n\n" \
+		"The special characters are @ (run after creating), $ (run before deleting),\n" \
+		"and * (run both after creating and before deleting).  The commands run in\n" \
+		"the /dev directory, and use system() which calls /bin/sh.\n\n" \
+	) \
 	"Config file parsing stops on the first matching line.  If no config\n"\
 	"entry is matched, devices are created with default 0:0 660.  (Make\n"\
-	"the last line match .* to override this.)\n\n"
-#endif
+	"the last line match .* to override this.)\n\n" \
+)
 
 #define mesg_trivial_usage \
 	"[y|n]"
diff --git a/util-linux/Config.in b/util-linux/Config.in
index a493fbf..501ed6b 100644
--- a/util-linux/Config.in
+++ b/util-linux/Config.in
@@ -265,16 +265,31 @@ config CONFIG_FEATURE_MDEV_CONF
 
 	  That's device name (with regex match), uid:gid, and permissions.
 
-	  Optionally, that can be followed (on the same line) by an asterisk
-	  and a command line to run after creating the corresponding device(s),
-	  ala:
-
-	    hdc root:cdrom 660  *ln -s hdc cdrom
-
 	  Config file parsing stops on the first matching line.  If no config
 	  entry is matched, devices are created with default 0:0 660.  (Make
 	  the last line match .* to override this.)
 
+config CONFIG_FEATURE_MDEV_EXEC
+	bool "Support command execution at device addition/removal"
+	default n
+	depends on CONFIG_FEATURE_MDEV_CONF
+	help
+	  This adds support for an optional field to /etc/mdev.conf, consisting
+	  of a special character and a command line to run after creating the
+	  corresponding device(s) and before removing, ala:
+
+	    hdc root:cdrom 660  *ln -s $MDEV cdrom
+
+	  The $MDEV environment variable is set to the name of the device.
+
+	  The special characters and their meanings are:
+	    @ Run after creating the device.
+	    $ Run before removing the device.
+	    * Run both after creating and before removing the device.
+
+	  Commands are executed via system() so you need /bin/sh, meaning you
+	  probably want to select a default shell in the Shells menu.
+
 config CONFIG_MKSWAP
 	bool "mkswap"
 	default n
diff --git a/util-linux/mdev.c b/util-linux/mdev.c
index 73a8231..3c7cf7b 100644
--- a/util-linux/mdev.c
+++ b/util-linux/mdev.c
@@ -8,25 +8,14 @@
  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
  */
 
+#include "busybox.h"
 #include <ctype.h>
-#include <dirent.h>
 #include <errno.h>
-#include <fcntl.h>
-#include <stdio.h>
-#include <string.h>
 #include <sys/mman.h>
-#include <sys/stat.h>
 #include <sys/sysmacros.h>
-#include <sys/types.h>
-#include <unistd.h>
-#include <stdlib.h>
-#include "busybox.h"
 #include "xregex.h"
 
 #define DEV_PATH	"/dev"
-#define MDEV_CONF	"/etc/mdev.conf"
-
-#include <busybox.h>
 
 struct mdev_globals
 {
@@ -36,14 +25,15 @@ struct mdev_globals
 #define bbg mdev_globals
 
 /* mknod in /dev based on a path like "/sys/block/hda/hda1" */
-static void make_device(char *path)
+static void make_device(char *path, int delete)
 {
-	char *device_name, *s;
+	char *device_name;
 	int major, minor, type, len, fd;
 	int mode = 0660;
 	uid_t uid = 0;
 	gid_t gid = 0;
 	char *temp = path + strlen(path);
+	char *command = NULL;
 
 	/* 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
@@ -69,7 +59,7 @@ static void make_device(char *path)
 		char *conf, *pos, *end;
 
 		/* mmap the config file */
-		if (-1 != (fd=open(MDEV_CONF,O_RDONLY))) {
+		if (-1 != (fd=open("/etc/mdev.conf",O_RDONLY))) {
 			len = lseek(fd, 0, SEEK_END);
 			conf = mmap(NULL, len, PROT_READ, MAP_PRIVATE, fd, 0);
 			if (conf) {
@@ -86,88 +76,89 @@ static void make_device(char *path)
 						;
 
 					/* Three fields: regex, uid:gid, mode */
-					for (field=3; field; field--) {
+					for (field=0; field < (3 + ENABLE_FEATURE_MDEV_EXEC);
+							field++)
+					{
 						/* Skip whitespace */
-						while (pos<end && isspace(*pos))
-							pos++;
-						if (pos==end || *pos=='#')
-							break;
-						for (end2=pos; end2<end && !isspace(*end2) && *end2!='#'; end2++)
+						while (pos<end && isspace(*pos)) pos++;
+						if (pos==end || *pos=='#') break;
+						for (end2=pos;
+							end2<end && !isspace(*end2) && *end2!='#'; end2++)
 							;
 
-						switch (field) {
+						if (!field) {
 							/* Regex to match this device */
-							case 3:
-							{
-								char *regex = strndupa(pos,end2-pos);
-								regex_t match;
-								regmatch_t off;
-								int result;
-
-								/* Is this it? */
-								xregcomp(&match,regex,REG_EXTENDED);
-								result = regexec(&match,device_name,1,&off,0);
-								regfree(&match);
-
-								/* If not this device, skip rest of line */
-								if (result || off.rm_so || off.rm_eo!=strlen(device_name))
-									goto end_line;
 
+							char *regex = strndupa(pos, end2-pos);
+							regex_t match;
+							regmatch_t off;
+							int result;
+
+							/* Is this it? */
+							xregcomp(&match,regex, REG_EXTENDED);
+							result = regexec(&match, device_name, 1, &off, 0);
+							regfree(&match);
+
+							/* If not this device, skip rest of line */
+							if (result || off.rm_so
+									|| off.rm_eo != strlen(device_name))
 								break;
-							}
+
+						} else if (field == 1) {
 							/* uid:gid */
-							case 2:
-							{
-								char *s2;
-
-								/* Find : */
-								for(s=pos; s<end2 && *s!=':'; s++)
-									;
-								if (s == end2)
-									goto end_line;
-
-								/* Parse UID */
-								uid = strtoul(pos,&s2,10);
-								if (s != s2) {
-									struct passwd *pass;
-									pass = getpwnam(strndupa(pos,s-pos));
-									if (!pass)
-										goto end_line;
-									uid = pass->pw_uid;
-								}
-								s++;
-								/* parse GID */
-								gid = strtoul(s,&s2,10);
-								if (end2 != s2) {
-									struct group *grp;
-									grp = getgrnam(strndupa(s,end2-s));
-									if (!grp)
-										goto end_line;
-									gid = grp->gr_gid;
-								}
-								break;
+
+							char *s, *s2;
+
+							/* Find : */
+							for(s=pos; s<end2 && *s!=':'; s++)
+								;
+							if (s == end2) break;
+
+							/* Parse UID */
+							uid = strtoul(pos,&s2,10);
+							if (s != s2) {
+								struct passwd *pass;
+								pass = getpwnam(strndupa(pos, s-pos));
+								if (!pass) break;
+								uid = pass->pw_uid;
+							}
+							s++;
+							/* parse GID */
+							gid = strtoul(s, &s2, 10);
+							if (end2 != s2) {
+								struct group *grp;
+								grp = getgrnam(strndupa(s, end2-s));
+								if (!grp) break;
+								gid = grp->gr_gid;
 							}
+						} else if (field == 2) {
 							/* mode */
-							case 1:
-							{
-								mode = strtoul(pos,&pos,8);
-								if (pos != end2)
-									goto end_line;
-								else
-									goto found_device;
+
+							mode = strtoul(pos, &pos, 8);
+							if (pos != end2) break;
+						} else if (ENABLE_FEATURE_MDEV_EXEC && field == 3) {
+							// Command to run
+							char *s = "@$*", *s2;
+							if (!(s2 = strchr(s, *pos++))) {
+							  	// Force error
+								field = 1;
+								break;
 							}
+							if ((s2-s+1) & (1<<delete))
+								command = bb_xstrndup(pos, end-pos);
 						}
+
 						pos = end2;
 					}
-end_line:
+
 					/* Did everything parse happily? */
-					if (field && field!=3)
-						bb_error_msg_and_die("Bad line %d",line);
+
+					if (field > 2) break;
+					if (field) bb_error_msg_and_die("Bad line %d",line);
 
 					/* Next line */
 					pos = ++end;
 				}
-found_device:
 				munmap(conf, len);
 			}
 			close(fd);
@@ -175,13 +166,29 @@ found_device:
 	}
 
 	umask(0);
-	if (mknod(device_name, mode | type, makedev(major, minor)) && errno != EEXIST)
-		bb_perror_msg_and_die("mknod %s failed", device_name);
+	if (!delete) {
+		if (mknod(device_name, mode | type, makedev(major, minor)) && errno != EEXIST)
+			bb_perror_msg_and_die("mknod %s failed", device_name);
 
-	if (major==bbg.root_major && minor==bbg.root_minor)
-		symlink(device_name, "root");
+		if (major == bbg.root_major && minor == bbg.root_minor)
+			symlink(device_name, "root");
 	
-	if (ENABLE_FEATURE_MDEV_CONF) chown(device_name, uid, gid);
+		if (ENABLE_FEATURE_MDEV_CONF) chown(device_name, uid, gid);
+	}
+	if (command) {
+		int rc;
+		char *s;
+		
+		s=bb_xasprintf("MDEV=%s",device_name);
+		putenv(s);
+		rc = system(command);
+		s[4]=0;
+		putenv(s);
+		free(s);
+		free(command);
+		if (rc == -1) bb_perror_msg_and_die("Couldn't run %s", command);
+	}
+	if (delete) unlink(device_name);
 }
 
 /* Recursive search of /sys/block or /sys/class.  path must be a writeable
@@ -212,7 +219,7 @@ static void find_dev(char *path)
 
 		/* If there's a dev entry, mknod it */
 
-		if (!strcmp(entry->d_name, "dev")) make_device(path);
+		if (!strcmp(entry->d_name, "dev")) make_device(path, 0);
 	}
 
 	closedir(dir);
@@ -247,12 +254,9 @@ int mdev_main(int argc, char *argv[])
 	    if (!action || !env_path)
 			bb_show_usage();
 
-		if (!strcmp(action, "add")) {
-			sprintf(temp, "/sys%s", env_path);
-			make_device(temp);
-		} else if (!strcmp(action, "remove")) {
-			unlink(strrchr(env_path, '/') + 1);
-		}
+		sprintf(temp, "/sys%s", env_path);
+		if (!strcmp(action, "add")) make_device(temp,0);
+		else if (!strcmp(action, "remove")) make_device(temp,1);
 	}
 
 	if (ENABLE_FEATURE_CLEAN_UP) RELEASE_CONFIG_BUFFER(temp);