mdev: add "!" syntax support

Based on the patch by Steve Bennett <steveb@workware.net.au>

function                                             old     new   delta
make_device                                         1640    1673     +33

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 43 insertions, 24 deletions

diff --git a/docs/mdev.txt b/docs/mdev.txt
index 7bd00fe1b..2d03bd8b2 100644
--- a/docs/mdev.txt
+++ b/docs/mdev.txt
@@ -51,8 +51,8 @@ device nodes if your system needs something more than the default root/root
 660 permissions.
 
 The file has the format:
-    <device regex>       <uid>:<gid> <octal permissions>
- or @<maj[,min1[-min2]]> <uid>:<gid> <octal permissions>
+    <device regex>       <uid>:<gid> <permissions>
+ or @<maj[,min1[-min2]]> <uid>:<gid> <permissions>
 
 For example:
     hd[a-z][0-9]* 0:3 660
@@ -63,7 +63,7 @@ create your own total match like so:
         .* 1:1 777
 
 You can rename/move device nodes by using the next optional field.
-        <device regex> <uid>:<gid> <octal permissions> [=path]
+        <device regex> <uid>:<gid> <permissions> [=path]
 So if you want to place the device node into a subdirectory, make sure the path
 has a trailing /.  If you want to rename the device node, just place the name.
         hda 0:3 660 =drives/
@@ -74,11 +74,17 @@ This will rename "hdb" to "cdrom".
 Similarly, ">path" renames/moves the device but it also creates
 a direct symlink /dev/DEVNAME to the renamed/moved device.
 
+You can also prevent creation of device nodes with the 4th field as "!":
+        tty[a-z]. 0:0 660 !
+        pty[a-z]. 0:0 660 !
+
 If you also enable support for executing your own commands, then the file has
 the format:
-        <device regex> <uid>:<gid> <octal permissions> [=path] [@|$|*<command>]
+        <device regex> <uid>:<gid> <permissions> [=path] [@|$|*<command>]
+    or
+        <device regex> <uid>:<gid> <permissions> [>path] [@|$|*<command>]
     or
-        <device regex> <uid>:<gid> <octal permissions> [>path] [@|$|*<command>]
+        <device regex> <uid>:<gid> <permissions> [!] [@|$|*<command>]
 
 For example:
 ---8<---
diff --git a/util-linux/mdev.c b/util-linux/mdev.c
index b0efd98b5..217075660 100644
--- a/util-linux/mdev.c
+++ b/util-linux/mdev.c
@@ -204,7 +204,8 @@ static void make_device(char *path, int delete)
                                 if (major < 0)
                                         continue; /* no dev, no match */
                                 sc = sscanf(val, "@%u,%u-%u", &cmaj, &cmin0, &cmin1);
-                                if (sc < 1 || major != cmaj
+                                if (sc < 1
+                                 || major != cmaj
                                  || (sc == 2 && minor != cmin0)
                                  || (sc == 3 && (minor < cmin0 || minor > cmin1))
                                 ) {
@@ -243,7 +244,8 @@ static void make_device(char *path, int delete)
 
                                 /* If no match, skip rest of line */
                                 /* (regexec returns whole pattern as "range" 0) */
-                                if (result || off[0].rm_so
+                                if (result
+                                 || off[0].rm_so
                                  || ((int)off[0].rm_eo != (int)strlen(str_to_match))
                                 ) {
                                         continue; /* this line doesn't match */
@@ -258,28 +260,34 @@ static void make_device(char *path, int delete)
                                 bb_error_msg("unknown user/group %s on line %d", tokens[1], parser->lineno);
 
                         /* 3rd field: mode - device permissions */
-                        /* mode = strtoul(tokens[2], NULL, 8); */
                         bb_parse_mode(tokens[2], &mode);
 
                         val = tokens[3];
-                        /* 4th field (opt): >|=alias */
+                        /* 4th field (opt): ">|=alias" or "!" to not create the node */
 
                         if (ENABLE_FEATURE_MDEV_RENAME && val) {
-                                aliaslink = val[0];
-                                if (aliaslink == '>' || aliaslink == '=') {
-                                        char *a, *s, *st;
-                                        char *p;
-                                        unsigned i, n;
-
-                                        a = val;
-                                        s = strchrnul(val, ' ');
-                                        st = strchrnul(val, '\t');
-                                        if (st < s)
-                                                s = st;
-                                        val = (s[0] && s[1]) ? s+1 : NULL;
+                                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 */
+                                        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;
@@ -323,8 +331,13 @@ static void make_device(char *path, int delete)
                                 /* Are we running this command now?
                                  * Run $cmd on delete, @cmd on create, *cmd on both
                                  */
-                                if (s2-s != delete)
+                                if (s2 - s != delete) {
+                                        /* We are here if: '*',
+                                         * or: '@' and delete = 0,
+                                         * or: '$' and delete = 1
+                                         */
                                         command = xstrdup(val + 1);
+                                }
                         }
                 }
 
@@ -368,7 +381,7 @@ static void make_device(char *path, int delete)
                                 free(command);
                         }
 
-                        if (delete) {
+                        if (delete && major >= 0) {
                                 if (ENABLE_FEATURE_MDEV_RENAME && alias) {
                                         if (aliaslink == '>')
                                                 unlink(device_name);