Refactor logbuffer_grow

Making a full copy of the logbuffer just to access four members
was not justified. The original idea was to re-use logbuffer_fini,
but, effectively, only buddy_return1_ptr_page() was called.

src/fellow_log.c

@@ -1906,14 +1906,22 @@ logbuffer_fini(struct fellow_logbuffer *lbuf)
 static void
 logbuffer_grow(struct fellow_logbuffer *lbuf, uint8_t initialbits)
 {
-	struct fellow_logbuffer old[1];
+	struct {
+		struct fellow_alloc_log_block	*arr;
+		struct buddy_ptr_page		alloc;	// arr allocation
+		unsigned			n, space;
+	} old;
 	size_t sz, b;
 
 	CHECK_OBJ_NOTNULL(lbuf, FELLOW_LOGBUFFER_MAGIC);
 	assert(lbuf->n == lbuf->space);
-	memcpy(old, lbuf, sizeof old);
 
-	if (old->alloc.bits == 0) {
+	old.arr		= lbuf->arr;
+	old.alloc	= lbuf->alloc;
+	old.n		= lbuf->n;
+	old.space	= lbuf->space;
+
+	if (old.alloc.bits == 0) {
 		AN(initialbits);
 		lbuf->alloc = buddy_alloc1_ptr_page_wait(
 		    lbuf->membuddy, FEP_LOG,
@@ -1921,7 +1929,7 @@ logbuffer_grow(struct fellow_logbuffer *lbuf, uint8_t initialbits)
 	} else {
 		AZ(initialbits);
 		lbuf->alloc = buddy_alloc1_ptr_page_wait(
-		    lbuf->membuddy, FEP_LOG, old->alloc.bits + 1, 0);
+		    lbuf->membuddy, FEP_LOG, old.alloc.bits + 1, 0);
 	}
 	MEM(lbuf->membuddy);
 	lbuf->arr = lbuf->alloc.ptr;
@@ -1933,24 +1941,12 @@ logbuffer_grow(struct fellow_logbuffer *lbuf, uint8_t initialbits)
 	assert(b < UINT_MAX);
 	lbuf->space = (unsigned)b;
 
-	if (old->space == 0)
+	if (old.space == 0)
 		return;
-	assert(lbuf->space > old->space);
-	if (old->n > 0) {
-		memcpy(lbuf->arr, old->arr, old->n * sizeof *lbuf->arr);
-		old->n = 0;
-	}
-	memset(&old->head, 0, sizeof old->head);
-	memset(&old->active, 0, sizeof old->active);
-	memset(&old->fdil, 0, sizeof old->fdil);
-	/* XXX we should REALLY rework the logbuffer and ff
-	 * in particular. For now, avoid logbuffer_fini to ALSO
-	 * wait on the copy (old) ...
-	 */
-	memset(&old->ff, 0, sizeof old->ff);
-	old->regions_to_free = NULL;
-	old->state = LBUF_FINI;
-	logbuffer_fini(old);
+	assert(lbuf->space > old.space);
+	if (old.n > 0)
+		memcpy(lbuf->arr, old.arr, old.n * sizeof *lbuf->arr);
+	buddy_return1_ptr_page(lbuf->membuddy, &old.alloc);
 }
 
 static void