warn when renaming kernel-provided nodes instead of adding symlinks

NEWS

@@ -1,5 +1,16 @@
 udev 154
 ========
+Bugfixes.
+
+Udev now gradually starts to pass control over the primary device nodes
+and their names to the kernel, and will in the end only manage the
+permissions of the node, and possibly create additional symlinks.
+As a first step NAME="" will be ignored, and NAME= setings with names
+other than the kernel provided name will result in a logged warning.
+Kernels that don't provide device names, or devtmpfs is not used, will
+still work as they did before, but it is strongly recommended to use
+only the same names for the primary device node as the recent kernel
+provides for all devices.
 
 udev 153
 ========

test/udev-test.pl

@@ -1263,17 +1263,6 @@ EOF
 KERNEL=="ttyACM[0-9]*", SYMLINK+="one"
 KERNEL=="ttyACM[0-9]*", SYMLINK+="two"
 KERNEL=="ttyACM[0-9]*", SYMLINK="three"
-EOF
-	},
-	{
-		desc		=> "test empty NAME",
-		subsys		=> "tty",
-		devpath		=> "/devices/pci0000:00/0000:00:1d.7/usb5/5-2/5-2:1.0/tty/ttyACM0",
-		exp_name	=> "<none>",
-		not_exp_name	=> "ttyACM0",
-		exp_add_error	=> "yes",
-		rules		=> <<EOF
-KERNEL=="ttyACM[0-9]*", NAME=""
 EOF
 	},
 	{

udev/udev-event.c

@@ -617,15 +617,20 @@ int udev_event_execute_rules(struct udev_event *event, struct udev_rules *rules)
 				}
 			}
 
-			if (event->name == NULL) {
+			if (event->name == NULL || event->name[0] == '\0') {
-				/* things went wrong */
 				udev_device_delete_db(dev);
 				udev_device_tag_index(dev, NULL, false);
 				udev_device_unref(event->dev_db);
 				err = -ENOMEM;
+				err(event->udev, "no node name, something went wrong, ignoring\n");
 				goto out;
 			}
 
+			if (udev_device_get_knodename(dev) != NULL && strcmp(udev_device_get_knodename(dev), event->name) != 0)
+				err(event->udev, "kernel-provided name '%s' and NAME= '%s' disagree, "
+				    "please use SYMLINK+= or change the kernel to provide the proper name\n",
+				    udev_device_get_knodename(dev), event->name);
+
 			/* set device node name */
 			util_strscpyl(filename, sizeof(filename), udev_get_dev_path(event->udev), "/", event->name, NULL);
 			udev_device_set_devnode(dev, filename);
@@ -639,23 +644,7 @@ int udev_event_execute_rules(struct udev_event *event, struct udev_rules *rules)
 			if (event->dev_db != NULL)
 				udev_node_update_old_links(dev, event->dev_db);
 
-			if (event->name[0] != '\0')
+			err = udev_node_add(dev, event->mode, event->uid, event->gid);
-				err = udev_node_add(dev, event->mode, event->uid, event->gid);
-			else
-				info(event->udev, "device node creation suppressed\n");
-
-			/* remove kernel-created node, if needed */
-			if (udev_device_get_knodename(dev) != NULL && strcmp(event->name, udev_device_get_knodename(dev)) != 0) {
-				struct stat stats;
-				char filename[UTIL_PATH_SIZE];
-
-				util_strscpyl(filename, sizeof(filename), udev_get_dev_path(event->udev), "/", udev_device_get_knodename(dev), NULL);
-				if (lstat(filename, &stats) == 0 && stats.st_rdev == udev_device_get_devnum(dev)) {
-					info(event->udev, "remove kernel created node '%s'\n", udev_device_get_knodename(dev));
-					util_unlink_secure(event->udev, filename);
-					util_delete_path(event->udev, filename);
-				}
-			}
 		}
 
 		udev_device_unref(event->dev_db);

udev/udev-rules.c

@@ -1468,9 +1468,13 @@ static int add_rule(struct udev_rules *rules, char *line,
 			if (op < OP_MATCH_MAX) {
 				rule_add_key(&rule_tmp, TK_M_NAME, op, value, NULL);
 			} else {
-				if (strcmp(value, "%k") == 0)
+				if (strcmp(value, "%k") == 0) {
-					err(rules->udev, "NAME=\"%%k\" is superfluous and breaks "
+					err(rules->udev, "NAME=\"%%k\" is ignored because it breaks kernel supplied names, "
-					    "kernel supplied names, please remove it from %s:%u\n", filename, lineno);
+					    "please remove it from %s:%u\n", filename, lineno);
+					continue;
+				}
+				if (value[0] == '\0')
+					continue;
 				rule_add_key(&rule_tmp, TK_A_NAME, op, value, NULL);
 			}
 			rule_tmp.rule.rule.flags = 1;

udev/udev.xml

@@ -18,23 +18,28 @@
 
       <refnamediv>
         <refname>udev</refname>
-        <refpurpose>dynamic device management</refpurpose>
+        <refpurpose>Linux dynamic device management</refpurpose>
       </refnamediv>
 
       <refsect1><title>DESCRIPTION</title>
-        <para>udev provides a dynamic device directory containing only the files for
+        <para>udev supplies the system software with device events, manages permissions
-        actually present devices. It creates or removes device node files in the
+        of device nodes and may create additional symlinks in the <filename>/dev</filename>
-        <filename>/dev</filename> directory, or it renames network interfaces.</para>
+        directory, or renames network interfaces. The kernel usually just assigns unpredictable
+        device names based on the order of discovery. Meaningful symlinks or network device
+        names provide a way to reliably identify devices based on their properties or
+        current configuration.</para>
 
-        <para>Usually udev runs as <citerefentry><refentrytitle>udevd</refentrytitle>
+        <para>The udev daemon <citerefentry><refentrytitle>udevd</refentrytitle>
-        <manvolnum>8</manvolnum></citerefentry> and receives uevents directly from the
+        <manvolnum>8</manvolnum></citerefentry> receives device uevents directly from
-        kernel if a device is added or removed from the system.</para>
+        the kernel whenever a device is added or removed from the system, or it changes its
+        state. When udev receives a device event, it matches its configured set of rules
+        against various device attributes to identify the device. Rules that match, may
+        provide additional device information to be stored in the udev database, or information
+        to be used to create meaningful symlink names.</para>
 
-        <para>If udev receives a device event, it matches its configured rules
+        <para>All device information udev processes, is stored in the udev database and
-        against the available device attributes provided in sysfs to identify the device.
+        sent out to possible event subscribers. Access to all stored data and the event
-        Rules that match may provide additional device information or specify a device
+        sources are provided by the library libudev.</para>
-        node name and multiple symlink names and instruct udev to run additional programs
-        as part of the device event handling.</para>
       </refsect1>
 
       <refsect1><title>CONFIGURATION</title>
@@ -84,9 +89,9 @@
           If all match keys are matching against its value, the rule gets applied and the
           assign keys get the specified value assigned.</para>
 
-          <para>A matching rule may specify the name of the device node, add a symlink
+          <para>A matching rule may rename a network interface, add symlinks
-          pointing to the node, or run a specified program as part of the event handling.
+          pointing to the device node, or run a specified program as part of
-          If no matching rule is found, the default device node name is used.</para>
+          the event handling.</para>
 
           <para>A rule consists of a list of one or more key value pairs separated by
           a comma. Each key has a distinct operation, depending on the used operator. Valid
@@ -304,13 +309,17 @@
             <varlistentry>
               <term><option>NAME</option></term>
               <listitem>
-                <para>The name, a network interface should be renamed to, or the name
+                <para>The name, a network interface should be renamed to. Or as
-                a device node should be named. Usually the kernel provides the defined
+                a temporary workaraound, the name a device node should be named.
-                node name, or even creates and removes the node before udev receives
+                Usually the kernel provides the defined node name, or even creates
-                any event. Changing the node name from the kernel's default may result
+                and removes the node before udev even receives any event. Changing
-                in unexpected behavior and is not supported. Udev is only expected to
+                the node name from the kernel's default creates inconsistencies
-                handle device node permissions and to create additional symlinks, which
+                and is not supported. If the kernel and NAME specify different names,
-                do not conflict with the kernel device node names.</para>
+                an error will be logged. Udev is only expected to handle device node
+                permissions and to create additional symlinks, not to change
+                kernel-provided device node names. Instead of renaming a device node,
+                SYMLINK should be used. Symlink names must never conflict with
+                device node names, it will result in unpredictable behavior.</para>
               </listitem>
             </varlistentry>
 
@@ -318,15 +327,15 @@
               <term><option>SYMLINK</option></term>
               <listitem>
                 <para>The name of a symlink targeting the node. Every matching rule will add
-                this value to the list of symlinks to be created along with the device node.
+                this value to the list of symlinks to be created. Multiple symlinks may be
-                Multiple symlinks may be specified by separating the names by the space
+                specified by separating the names by the space character. In case multiple
-                character. In case multiple devices claim the same name, the link will
+                devices claim the same name, the link will always point to the device with
-                always point to the device with the highest link_priority. If the current device
+                the highest link_priority. If the current device goes away, the links will
-                goes away, the links will be re-evaluated and the device with the next highest
+                be re-evaluated and the device with the next highest link_priority will own
-                link_priority will own the link. If no link_priority is specified, the order
+                the link. If no link_priority is specified, the order of the devices, and
-                of the devices, and which of them will own the link, is undefined. Claiming
+                which one of them will own the link, is undefined. Claiming the same name for
-                the same name for a node and links may result in unexpected behavior and is
+                a symlink, which is or might be used for a device node, may result in
-                not supported.
+                unexpected behavior and is not supported.
                 </para>
               </listitem>
             </varlistentry>
@@ -379,18 +388,10 @@
                 <option>RUN{<replaceable>fail_event_on_error</replaceable>}</option> is
                 specified, and the executed program returns non-zero, the event will be
                 marked as failed for a possible later handling.</para>
-                <para>If no path is given, the program must be in 
+                <para>If no absolute path is given, the program is expected to live in
-                <filename>/lib/udev</filename>, otherwise the full path must be
+                <filename>/lib/udev</filename>, otherwise the absolute path must be
-                specified.</para>
+                specified. Program name and arguments are separated by spaces. Single quotes
-                <para>If the specified string starts with
+                can be used to specify arguments with spaces.</para>
-                <option>socket:<replaceable>path</replaceable></option>, all current event
-                values will be passed to the specified socket, as a message in the same
-                format the kernel sends an uevent. If the first character of the specified path
-                is an @ character, an abstract namespace socket is used, instead of an existing
-                socket file.</para>
-                <para>Program name and arguments are separated with spaces. To
-                include spaces in an argument, use single quotes. Please note
-                that this does not run through a shell.</para>
               </listitem>
             </varlistentry>