[PATCH 1/2] leds: accept trigger parameters in "trigger:params" format

[Mieczyslaw Nalewaj <namiltd@yahoo.com>]

Allow parameters to be passed along with the trigger name when
writing to /sys/class/leds/<led>/trigger in the format:
  echo "trigger_name:params" > /sys/class/leds/<led>/trigger

Core stores the RHS in led_cdev->params for the duration of the
activate() call; triggers may read and optionally consume or copy it.
Core frees any remaining buffer after activate() returns.

Signed-off-by: Mieczyslaw Nalewaj <namiltd@yahoo.com>

--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -33,6 +33,12 @@ trigger_relevant(struct led_classdev *le
     return !trig->trigger_type || trig->trigger_type == led_cdev->trigger_type;
 }
 
+/* 
+ * core: accept "<trigger>" or "<trigger>:<params>" and pass params via led_cdev->params.
+ * - If a colon is present, the RHS is duplicated and stored in led_cdev->params.
+ * - The trigger's activate callback may consume the pointer (free it and set to NULL).
+ * - If the trigger does not consume it, core frees the buffer after activate returns.
+ */
 ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
               struct bin_attribute *bin_attr, char *buf,
               loff_t pos, size_t count)
@@ -41,6 +47,10 @@ ssize_t led_trigger_write(struct file *f
     struct led_classdev *led_cdev = dev_get_drvdata(dev);
     struct led_trigger *trig;
     int ret = count;
+    char *tmp = NULL;
+    char *params = NULL;
+    char *pcolon;
+    bool found = false;
 
     mutex_lock(&led_cdev->led_access);
 
@@ -49,26 +59,81 @@ ssize_t led_trigger_write(struct file *f
         goto unlock;
     }
 
-    if (sysfs_streq(buf, "none")) {
-        led_trigger_remove(led_cdev);
+    /* copy input and NUL-terminate; trim trailing newline if present */
+    tmp = kstrndup(buf, count, GFP_KERNEL);
+    if (!tmp) {
+        ret = -ENOMEM;
         goto unlock;
     }
+    if (strlen(tmp) && tmp[strlen(tmp) - 1] == '\n')
+        tmp[strlen(tmp) - 1] = '\0';
+
+    /* handle special keywords */
+    if (sysfs_streq(tmp, "none")) {
+        led_trigger_remove(led_cdev);
+        goto out_free;
+    }
+    if (sysfs_streq(tmp, "default")) {
+        led_trigger_set_default(led_cdev);
+        goto out_free;
+    }
+
+    /* split on first ':' to accept "<trigger>" or "<trigger>:<params>" */
+    pcolon = strchr(tmp, ':');
+    if (pcolon) {
+        *pcolon = '\0';
+        params = kstrdup(pcolon + 1, GFP_KERNEL);
+        if (!params) {
+            ret = -ENOMEM;
+            goto out_free;
+        }
+    }
 
     down_read(&triggers_list_lock);
     list_for_each_entry(trig, &trigger_list, next_trig) {
-        if (sysfs_streq(buf, trig->name) && trigger_relevant(led_cdev, trig)) {
+        if (!trigger_relevant(led_cdev, trig))
+            continue;
+
+        if (sysfs_streq(tmp, trig->name)) {
             down_write(&led_cdev->trigger_lock);
+
+            /* attach transient params to led_cdev before setting trigger */
+            if (params) {
+                kfree(led_cdev->params);
+                led_cdev->params = params;
+                params = NULL; /* ownership transferred */
+            } else {
+                kfree(led_cdev->params);
+                led_cdev->params = NULL;
+            }
+
+            /* set the trigger (this will call trig->activate/led_trigger_set) */
             led_trigger_set(led_cdev, trig);
             up_write(&led_cdev->trigger_lock);
 
-            up_read(&triggers_list_lock);
-            goto unlock;
+            found = true;
+            break;
         }
     }
-    /* we come here only if buf matches no trigger */
-    ret = -EINVAL;
     up_read(&triggers_list_lock);
 
+    if (!found) {
+        /* no matching trigger name found */
+        ret = -EINVAL;
+        goto out_free;
+    }
+
+    /* If the trigger didn't consume the transient params, free it now. */
+    down_write(&led_cdev->trigger_lock);
+    if (led_cdev->params) {
+        kfree(led_cdev->params);
+        led_cdev->params = NULL;
+    }
+    up_write(&led_cdev->trigger_lock);
+
+out_free:
+    kfree(tmp);
+    kfree(params); /* free if not attached */
 unlock:
     mutex_unlock(&led_cdev->led_access);
     return ret;
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -240,6 +240,17 @@ struct led_classdev {
 
     /* Ensures consistent access to the LED class device */
     struct mutex        led_access;
+    /*
+     * Optional transient parameter provided by core when user writes
+     * "<trigger_name>:<param>" to /sys/class/leds/<led>/trigger.
+     * - Core allocates a NUL-terminated string and stores it here before
+     *   calling trigger->activate(led_cdev).
+     * - Trigger may "consume" the string by freeing it and setting the
+     *   pointer to NULL.
+     * - If the trigger does not consume it, core frees the buffer after
+     *   activate returns.
+     */
+    char *params;
 };
 
 /**