Illumos 5038 - Remove "old-style" flexible array usage in ZFS.

5038 Remove "old-style" flexible array usage in ZFS.
Author: Justin T. Gibbs <justing@spectralogic.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
Approved by: Richard Lowe <richlowe@richlowe.net>

References:
  https://www.illumos.org/issues/5038
  illumos/illumos-gate@7f18da4

Ported-by: Chris Dunlop <chris@onthe.net.au>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

Author: Justin T. Gibbs

include/sys/dnode.h

@@ -267,7 +267,7 @@ typedef struct dnode_handle {
 
 typedef struct dnode_children {
 	size_t dnc_count;		/* number of children */
-	dnode_handle_t dnc_children[1];	/* sized dynamically */
+	dnode_handle_t dnc_children[];	/* sized dynamically */
 } dnode_children_t;
 
 typedef struct free_range {

module/zfs/dnode.c

@@ -1022,7 +1022,7 @@ dnode_buf_pageout(dmu_buf_t *db, void *arg)
 		dnh->dnh_dnode = NULL;
 	}
 	kmem_free(children_dnodes, sizeof (dnode_children_t) +
-	    (epb - 1) * sizeof (dnode_handle_t));
+	    epb * sizeof (dnode_handle_t));
 }
 
 /*
@@ -1107,7 +1107,7 @@ dnode_hold_impl(objset_t *os, uint64_t object, int flag,
 		int i;
 		dnode_children_t *winner;
 		children_dnodes = kmem_alloc(sizeof (dnode_children_t) +
-		    (epb - 1) * sizeof (dnode_handle_t), KM_SLEEP);
+		    epb * sizeof (dnode_handle_t), KM_SLEEP);
 		children_dnodes->dnc_count = epb;
 		dnh = &children_dnodes->dnc_children[0];
 		for (i = 0; i < epb; i++) {
@@ -1122,7 +1122,7 @@ dnode_hold_impl(objset_t *os, uint64_t object, int flag,
 			}
 
 			kmem_free(children_dnodes, sizeof (dnode_children_t) +
-			    (epb - 1) * sizeof (dnode_handle_t));
+			    epb * sizeof (dnode_handle_t));
 			children_dnodes = winner;
 		}
 	}