zio-sysc.c: fix bug from patch 896e0664 and improve comments

The patch 896e0664

 misses to assign the zattr for the zio
extended attributes. This patch also improve comments to avoid
similar errors in the future.

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
Acked-by: Alessandro Rubini <rubinig@gnudd.com>

zio-sys.c

@@ -693,8 +693,7 @@ static int __zattr_chan_init_ctrl(struct zio_channel *chan, unsigned int start)
 	}
 
 	__zattr_trig_init_ctrl(cset->ti, chan->current_ctrl);
-
-	/* Copy channel attributes */
+	/* Copy standard attributes into the control */
 	for (i = 0; i < chan->zattr_set.n_std_attr; ++i)
 		__zattr_valcpy(ctrl_attr_chan, &chan->zattr_set.std_zattr[i]);
 	for (i = 0; i < cset->zattr_set.n_std_attr; ++i)
@@ -702,6 +701,7 @@ static int __zattr_chan_init_ctrl(struct zio_channel *chan, unsigned int start)
 	for (i = 0; i < zdev->zattr_set.n_std_attr; ++i)
 		__zattr_valcpy(ctrl_attr_chan, &zdev->zattr_set.std_zattr[i]);
 
+	/* Fix and copy attributes within channel */
 	zattr = chan->zattr_set.ext_zattr;
 	for (i = 0; i < chan->zattr_set.n_ext_attr; ++i) {
 		if (zattr[i].flags & ZIO_ATTR_CONTROL) {
@@ -712,15 +712,16 @@ static int __zattr_chan_init_ctrl(struct zio_channel *chan, unsigned int start)
 			zattr[i].index = ZIO_ATTR_INDEX_NONE;
 		}
 	}
-
+	/* Copying attributes from cset */
 	zattr = cset->zattr_set.ext_zattr;
 	for (i = 0; i < cset->zattr_set.n_ext_attr; ++i)
 		if (zattr[i].flags & ZIO_ATTR_CONTROL)
 			__zattr_valcpy(ctrl_attr_chan, &zattr[i]);
+	/* Copying attributes from zdev */
+	zattr = zdev->zattr_set.ext_zattr;
 	for (i = 0; i < zdev->zattr_set.n_ext_attr; ++i)
 		if (zattr[i].flags & ZIO_ATTR_CONTROL)
 			__zattr_valcpy(ctrl_attr_chan, &zattr[i]);
-
 	return 0;
 }
 static int __zattr_cset_init_ctrl(struct zio_cset *cset, unsigned int start)