Re: [patch] compatibility symlinks for udev

[David Zeuthen <david@fubar.dk>]

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On Mon, 2004-09-06 at 17:45 +0200, Kay Sievers wrote:
> On Mon, 2004-09-06 at 16:46 +0200, David Zeuthen wrote:
> 
> Nice, I like it. It's a easy way to group device nodes of the same type,
> but coming from different kernel subsystems.
> 

That's a good way of putting it, yeah.

> > Here's a patch against udev-030 that can help create compatibility
> > symlinks like /dev/cdrom, /dev/cdrom1 etc. The patch introduces a new
> > substitution type %C (for Compatibility) that can be used as follows
> 
> I suggest using %e for enumeration here, cause "compatibility" can
> easily be misunderstood.
> 

Good point, I've changed that.

> And we need a few lines added to the man page at udev.8.in :)
> 

Done. I've also added an example.

Also, Kay pointed out offlist that the rules can be written to not
require a shell script; this actually works

        KERNEL="sr*", NAME="%k", SYMLINK="cdrom%e"
        KERNEL="scd*", NAME="%k", SYMLINK="cdrom%e"
        KERNEL="pcd*", NAME="%k", SYMLINK="cdrom%e"
        KERNEL="hd[a-z]", PROGRAM="/bin/cat /proc/ide/%k/media", RESULT="cdrom", NAME="\%k", SYMLINK="cdrom%e"
        KERNEL="fd[0-9]", NAME="%k", SYMLINK="floppy%e"
        KERNEL="hd[a-z]", PROGRAM="/bin/cat /proc/ide/%k/media", RESULT="floppy", NAME=\"%k", SYMLINK="floppy%e"
        
New patch is attached. 

David


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--- udev-030.orig/namedev.c	2004-07-09 19:59:10.000000000 +0200
+++ udev-030/namedev.c	2004-09-07 12:50:09.599372960 +0200
@@ -42,6 +42,7 @@
 #include "logging.h"
 #include "namedev.h"
 #include "klibc_fixups.h"
+#include "udevdb.h"
 
 static struct sysfs_attribute *find_sysfs_attribute(struct sysfs_class_device *class_dev, struct sysfs_device *sysfs_device, char *attr);
 
@@ -179,6 +180,37 @@ static int get_format_len(char **str)
 	return -1;
 }
 
+/** Finds the lowest positive N such that <name>N isn't present in 
+ *  $(udevroot) either as a file or a symlink.
+ *
+ *  @param  name                Name to check for
+ *  @return                     0 if <name> didn't exist and N otherwise.
+ */
+static unsigned int find_free_number (struct udevice *udev, char *name)
+{
+	char temp[NAME_SIZE];
+	char path[NAME_SIZE];
+	struct udevice dev;
+	int result;
+
+	/* have to sweep the database for each lookup */
+	result = 0;
+	strncpy(temp, name, sizeof (temp));
+	while (1) {
+		if (udevdb_get_dev_byname(temp, path, &dev) != 0)
+			goto found;
+		/* symlink might be stale if $(udevroot) isn't cleaned; check
+		 * on major/minor to see if it's the same device
+		 */
+		if (dev.major == udev->major && dev.minor == udev->minor)
+			goto found;
+		snprintf (temp, sizeof(temp), "%s%d", name, ++result);
+	}
+
+found:
+	return result;
+}
+
 static void apply_format(struct udevice *udev, char *string, size_t maxsize,
 			 struct sysfs_class_device *class_dev,
 			 struct sysfs_device *sysfs_device)
@@ -195,6 +227,7 @@ static void apply_format(struct udevice 
 	char *rest;
 	int slen;
 	struct sysfs_attribute *tmpattr;
+	unsigned int next_free_number;
 
 	pos = string;
 	while (1) {
@@ -284,6 +317,13 @@ static void apply_format(struct udevice 
 			strfieldcatmax(string, "%", maxsize);
 			pos++;
 			break;
+		case 'e':
+			next_free_number = find_free_number(udev, string);
+			if (next_free_number > 0) {
+				snprintf(temp2, sizeof(temp2), "%d", next_free_number);
+				strfieldcatmax(string, temp2, maxsize);
+			}
+			break;
 		default:
 			dbg("unknown substitution type '%%%c'", c);
 			break;
--- udev-030.orig/udev.8.in	2004-07-09 19:59:10.000000000 +0200
+++ udev-030/udev.8.in	2004-09-07 13:12:58.660244072 +0200
@@ -272,6 +272,13 @@ all remaining parts of the result string
 .BI %s{ filename }
 The content of a sysfs attribute.
 .TP
+.B %e
+If a device node already exists with the name, the smallest positive
+decimal integer N is substituted such that the resulting name doesn't
+match an existing device node. Otherwise nothing is substituted. This
+can be used to create compatibility symlinks and enumerate devices of
+the same type originating from different kernel subsystems.
+.TP
 .B %%
 The '%' character itself.
 .P
@@ -302,6 +309,14 @@ KERNEL="ttyUSB1", NAME="pda", SYMLINK="p
 
 # multiple USB webcams with symlinks to be called webcam0, webcam1, ...
 BUS="usb", SYSFS{model}="XV3", NAME="video%n", SYMLINK="webcam%n"
+
+# grouping of optical drives from multiple kernel subsystems
+KERNEL="sr*", NAME="%k", SYMLINK="cdrom%e"
+KERNEL="scd*", NAME="%k", SYMLINK="cdrom%e"
+KERNEL="pcd*", NAME="%k", SYMLINK="cdrom%e"
+KERNEL="hd[a-z]", PROGRAM="/bin/cat /proc/ide/%k/media", RESULT="cdrom",
+  NAME="%k", SYMLINK="cdrom%e"
+
 .fi
 .P
 The permissions and ownership of the created device file is read from