Trim new line from zfs_vdev_scheduler

Add a helper function to trim the tailing new line.  While we're
here use this new hook to immediately apply the new scheduler.

Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #3356 
Closes #6573

module/zfs/vdev_disk.c

@@ -27,13 +27,14 @@
  */
 
 #include <sys/zfs_context.h>
-#include <sys/spa.h>
+#include <sys/spa_impl.h>
 #include <sys/vdev_disk.h>
 #include <sys/vdev_impl.h>
 #include <sys/abd.h>
 #include <sys/fs/zfs.h>
 #include <sys/zio.h>
 #include <sys/sunldi.h>
+#include <linux/mod_compat.h>
 
 char *zfs_vdev_scheduler = VDEV_SCHEDULER;
 static void *zfs_vdev_holder = VDEV_HOLDER;
@@ -113,15 +114,23 @@ vdev_disk_error(zio_t *zio)
  * physical device.  This yields the largest possible requests for
  * the device with the lowest total overhead.
  */
-static int
+static void
 vdev_elevator_switch(vdev_t *v, char *elevator)
 {
 	vdev_disk_t *vd = v->vdev_tsd;
-	struct block_device *bdev = vd->vd_bdev;
+	struct request_queue *q;
-	struct request_queue *q = bdev_get_queue(bdev);
+	char *device;
-	char *device = bdev->bd_disk->disk_name;
 	int error;
 
+	for (int c = 0; c < v->vdev_children; c++)
+		vdev_elevator_switch(v->vdev_child[c], elevator);
+
+	if (!v->vdev_ops->vdev_op_leaf || vd->vd_bdev == NULL)
+		return;
+
+	q = bdev_get_queue(vd->vd_bdev);
+	device = vd->vd_bdev->bd_disk->disk_name;
+
 	/*
 	 * Skip devices which are not whole disks (partitions).
 	 * Device-mapper devices are excepted since they may be whole
@@ -131,15 +140,15 @@ vdev_elevator_switch(vdev_t *v, char *elevator)
 	 * "Skip devices without schedulers" check below will fail.
 	 */
 	if (!v->vdev_wholedisk && strncmp(device, "dm-", 3) != 0)
-		return (0);
+		return;
 
 	/* Skip devices without schedulers (loop, ram, dm, etc) */
 	if (!q->elevator || !blk_queue_stackable(q))
-		return (0);
+		return;
 
 	/* Leave existing scheduler when set to "none" */
 	if ((strncmp(elevator, "none", 4) == 0) && (strlen(elevator) == 4))
-		return (0);
+		return;
 
 #ifdef HAVE_ELEVATOR_CHANGE
 	error = elevator_change(q, elevator);
@@ -156,20 +165,16 @@ vdev_elevator_switch(vdev_t *v, char *elevator)
 	"     2>/dev/null; " \
 	"echo %s"
 
-	{
 	char *argv[] = { "/bin/sh", "-c", NULL, NULL };
 	char *envp[] = { NULL };
 
 	argv[2] = kmem_asprintf(SET_SCHEDULER_CMD, device, elevator);
 	error = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_PROC);
 	strfree(argv[2]);
-	}
 #endif /* HAVE_ELEVATOR_CHANGE */
 	if (error)
 		printk("ZFS: Unable to set \"%s\" scheduler for %s (%s): %d\n",
 		    elevator, v->vdev_path, device, error);
-
-	return (error);
 }
 
 /*
@@ -798,6 +803,35 @@ vdev_disk_rele(vdev_t *vd)
 	/* XXX: Implement me as a vnode rele for the device */
 }
 
+static int
+param_set_vdev_scheduler(const char *val, zfs_kernel_param_t *kp)
+{
+	spa_t *spa = NULL;
+	char *p;
+
+	if (val == NULL)
+		return (SET_ERROR(-EINVAL));
+
+	if ((p = strchr(val, '\n')) != NULL)
+		*p = '\0';
+
+	mutex_enter(&spa_namespace_lock);
+	while ((spa = spa_next(spa)) != NULL) {
+		if (spa_state(spa) != POOL_STATE_ACTIVE ||
+		    !spa_writeable(spa) || spa_suspended(spa))
+			continue;
+
+		spa_open_ref(spa, FTAG);
+		mutex_exit(&spa_namespace_lock);
+		vdev_elevator_switch(spa->spa_root_vdev, (char *)val);
+		mutex_enter(&spa_namespace_lock);
+		spa_close(spa, FTAG);
+	}
+	mutex_exit(&spa_namespace_lock);
+
+	return (param_set_charp(val, kp));
+}
+
 vdev_ops_t vdev_disk_ops = {
 	vdev_disk_open,
 	vdev_disk_close,
@@ -812,5 +846,6 @@ vdev_ops_t vdev_disk_ops = {
 	B_TRUE			/* leaf vdev */
 };
 
-module_param(zfs_vdev_scheduler, charp, 0644);
+module_param_call(zfs_vdev_scheduler, param_set_vdev_scheduler,
+    param_get_charp, &zfs_vdev_scheduler, 0644);
 MODULE_PARM_DESC(zfs_vdev_scheduler, "I/O scheduler");