btrfs-progs: add an extensible pointer array struct

API for extensible array of pointers for covenience. A simple wrapper
around a (void *) array with length.

Signed-off-by: David Sterba <dsterba@suse.com>

Makefile

@@ -194,6 +194,7 @@ objects = \
 	kernel-shared/uuid-tree.o	\
 	kernel-shared/volumes.o	\
 	kernel-shared/zoned.o	\
+	common/array.o		\
 	common/cpu-utils.o	\
 	common/device-scan.o	\
 	common/device-utils.o	\

common/array.c

@@ -0,0 +1,99 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#define _GNU_SOURCE 1
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "common/array.h"
+
+/*
+ * Extensible array of pointers. Length is the number of user defined pointers,
+ * capacity is the whole allocated size. Pointers are potentially unstable after
+ * an append operation. Array initialized to all zeros is valid and can be extended.
+ */
+
+static const int alloc_increment = 32;
+
+/* Initialize new array, preallocate @capacity elemennts. */
+int array_init(struct array *arr, unsigned int capacity)
+{
+	void *tmp;
+
+	arr->data = NULL;
+	arr->length = 0;
+	arr->capacity = capacity;
+	if (arr->capacity == 0)
+		arr->capacity = alloc_increment;
+
+	tmp = calloc(arr->capacity, sizeof(void *));
+	if (!tmp)
+		return -1;
+	arr->data = tmp;
+	return 0;
+}
+
+/* Free internal data array. */
+void array_free(struct array *arr)
+{
+	free(arr->data);
+	arr->length = 0;
+	arr->capacity = 0;
+	arr->data = NULL;
+}
+
+/* Free all elements up to length. */
+void array_free_elements(struct array *arr)
+{
+	unsigned int i;
+
+	for (i = 0; i < arr->length; i++) {
+		free(arr->data[i]);
+		arr->data[i] = NULL;
+	}
+	arr->length = 0;
+}
+
+/* Reset all elements to NULL up to capacity. */
+void array_clear(struct array *arr)
+{
+	for (unsigned int i = 0; i < arr->capacity; i++)
+		arr->data[i] = NULL;
+}
+
+/* Use the whole capacity for elements. */
+void array_use_capacity(struct array *arr)
+{
+	arr->length = arr->capacity;
+}
+
+/* Append a new element (increas length), extend the array if needed. */
+int array_append(struct array *arr, void *element)
+{
+	if (arr->length == arr->capacity) {
+		void **tmp;
+
+		tmp = realloc(arr->data, (arr->capacity + alloc_increment) * sizeof(void *));
+		if (!tmp)
+			return -1;
+		arr->data = tmp;
+		memset(&arr->data[arr->capacity], 0, alloc_increment * sizeof(void *));
+		arr->capacity += alloc_increment;
+	}
+	arr->data[arr->length] = element;
+	arr->length++;
+	return 0;
+}

common/array.h

@@ -0,0 +1,36 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#ifndef __COMMON_ARRAY_H__
+#define __COMMON_ARRAY_H__
+
+/*
+ * Extensible array of pointers.
+ */
+struct array {
+	void **data;
+	unsigned int length;
+	unsigned int capacity;
+};
+
+int array_init(struct array *arr, unsigned int capacity);
+void array_free(struct array *arr);
+void array_free_elements(struct array *arr);
+void array_clear(struct array *arr);
+void array_use_capacity(struct array *arr);
+int array_append(struct array *arr, void *element);
+
+#endif