let $attr{symlink} return the last element of the path

Example for /block/sda:
  SUBSYSTEMS="scsi", ENV{COMMENT}="$attr{driver}"
sets COMMENT=sd
  SUBSYSTEMS="pci", ENV{COMMENT}="$attr{driver}"
sets COMMENT=ata_piix

3 files changed, 92 insertions, 38 deletions

diff --git a/test/udev-test.pl b/test/udev-test.pl
index 464098fa65..54c3378392 100755
--- a/test/udev-test.pl
+++ b/test/udev-test.pl
@@ -582,6 +582,24 @@ SUBSYSTEMS=="scsi", KERNELS=="0:0:0:0", NAME="bad"
 EOF
 	},
 	{
+		desc		=> "substitute attr with link target value (first match)",
+		subsys		=> "block",
+		devpath		=> "/block/sda",
+		exp_name	=> "driver-is-sd",
+		rules		=> <<EOF
+SUBSYSTEMS=="scsi", NAME="driver-is-\$attr{driver}"
+EOF
+	},
+	{
+		desc		=> "substitute attr with link target value (currently selected device)",
+		subsys		=> "block",
+		devpath		=> "/block/sda",
+		exp_name	=> "driver-is-aic7xxx",
+		rules		=> <<EOF
+SUBSYSTEMS=="pci", NAME="driver-is-\$attr{driver}"
+EOF
+	},
+	{
 		desc		=> "ignore ATTRS attribute whitespace",
 		subsys		=> "block",
 		devpath		=> "/block/sda",
diff --git a/udev_rules.c b/udev_rules.c
index 1483f8f493..edaaa71d12 100644
--- a/udev_rules.c
+++ b/udev_rules.c
@@ -458,30 +458,42 @@ found:
 			}
 			break;
 		case SUBST_ATTR:
-			if (attr == NULL) {
-				dbg("missing attribute");
-				break;
-			} else {
-				struct sysfs_device *dev_parent;
-				const char *value;
+			if (attr == NULL)
+				err("missing file parameter for attr");
+			else {
+				const char *value = NULL;
+				size_t size;
+
+				/* first try the current device, other matches may have selected */
+				if (udev->dev_parent != NULL && udev->dev_parent != udev->dev)
+					value = sysfs_attr_get_value(udev->dev_parent->devpath, attr);
+
+				/* look at all devices along the chain of parents */
+				if (value == NULL) {
+					struct sysfs_device *dev_parent = udev->dev;
+
+					do {
+						dbg("looking at '%s'", dev_parent->devpath);
+						value = sysfs_attr_get_value(dev_parent->devpath, attr);
+						if (value != NULL) {
+							strlcpy(temp2, value, sizeof(temp2));
+							break;
+						}
+						dev_parent = sysfs_device_get_parent(dev_parent);
+					} while (dev_parent != NULL);
+				}
 
-				dev_parent = udev->dev;
-				do {
-					dbg("looking at '%s'", dev_parent->devpath);
-					value = sysfs_attr_get_value(dev_parent->devpath, attr);
-					if (value != NULL) {
-						strlcpy(temp2, value, sizeof(temp2));
-						break;
-					}
-					dev_parent = sysfs_device_get_parent(dev_parent);
-				} while (dev_parent != NULL);
+				if (value == NULL)
+					break;
 
-				/* strip trailing whitespace of sysfs value */
-				i = strlen(temp2);
-				while (i > 0 && isspace(temp2[i-1]))
-					temp2[--i] = '\0';
+				/* strip trailing whitespace and replace untrusted characters of sysfs value */
+				size = strlcpy(temp2, value, sizeof(temp2));
+				if (size >= sizeof(temp2))
+					size = sizeof(temp2)-1;
+				while (size > 0 && isspace(temp2[size-1]))
+					temp2[--size] = '\0';
 				count = replace_untrusted_chars(temp2);
-				if (count)
+				if (count > 0)
 					info("%i untrusted character(s) replaced" , count);
 				strlcat(string, temp2, maxsize);
 				dbg("substitute sysfs value '%s'", temp2);
@@ -693,7 +705,7 @@ static int match_rule(struct udevice *udev, struct udev_rule *rule)
 		if (match_key("DRIVERS", rule, &rule->drivers, udev->dev_parent->driver))
 			goto try_parent;
 
-		/* check for matching sysfs attrubute pairs */
+		/* check for matching sysfs attribute pairs */
 		for (i = 0; i < rule->attrs.count; i++) {
 			struct key_pair *pair = &rule->attrs.keys[i];
 
diff --git a/udev_sysfs.c b/udev_sysfs.c
index c192696689..e733d417c5 100644
--- a/udev_sysfs.c
+++ b/udev_sysfs.c
@@ -346,6 +346,7 @@ char *sysfs_attr_get_value(const char *devpath, const char *attr_name)
 	char value[NAME_SIZE];
 	struct sysfs_attr *attr_loop;
 	struct sysfs_attr *attr;
+	struct stat statbuf;
 	int fd;
 	ssize_t size;
 	size_t sysfs_len;
@@ -375,25 +376,48 @@ char *sysfs_attr_get_value(const char *devpath, const char *attr_name)
 	dbg("add to cache '%s'", path_full);
 	list_add(&attr->node, &attr_list);
 
-	/* read attribute value */
-	fd = open(path_full, O_RDONLY);
-	if (fd < 0) {
-		dbg("attribute '%s' does not exist", path_full);
+	if (lstat(path_full, &statbuf) != 0) {
+		dbg("stat '%s' failed: %s", path_full, strerror(errno));
 		goto out;
 	}
-	size = read(fd, value, sizeof(value));
-	close(fd);
-	if (size < 0)
-		goto out;
-	if (size == sizeof(value))
-		goto out;
 
-	/* got a valid value, store and return it */
-	value[size] = '\0';
-	remove_trailing_chars(value, '\n');
-	dbg("cache '%s' with value '%s'", path_full, value);
-	strlcpy(attr->value_local, value, sizeof(attr->value_local));
-	attr->value = attr->value_local;
+	if (S_ISLNK(statbuf.st_mode)) {
+		/* links return the last element of the target path */
+		char link_target[PATH_SIZE];
+		int len;
+		const char *pos;
+
+		len = readlink(path_full, link_target, sizeof(link_target));
+		if (len > 0) {
+			link_target[len] = '\0';
+			pos = strrchr(link_target, '/');
+			if (pos != NULL) {
+				dbg("cache '%s' with link value '%s'", path_full, value);
+				strlcpy(attr->value_local, &pos[1], sizeof(attr->value_local));
+				attr->value = attr->value_local;
+			}
+		}
+	} else {
+		/* read attribute value */
+		fd = open(path_full, O_RDONLY);
+		if (fd < 0) {
+			dbg("attribute '%s' does not exist", path_full);
+			goto out;
+		}
+		size = read(fd, value, sizeof(value));
+		close(fd);
+		if (size < 0)
+			goto out;
+		if (size == sizeof(value))
+			goto out;
+
+		/* got a valid value, store and return it */
+		value[size] = '\0';
+		remove_trailing_chars(value, '\n');
+		dbg("cache '%s' with attribute value '%s'", path_full, value);
+		strlcpy(attr->value_local, value, sizeof(attr->value_local));
+		attr->value = attr->value_local;
+	}
 
 out:
 	return attr->value;