cbfstool: Add helper function buffer_from_file_aligned_size

This change adds a helper function `buffer_from_file_aligned_size`
that loads a file into memory buffer by creating a memory buffer of
size rounded up to the provided `size_granularity` parameter.

BUG=b:189177186,b:189167923

Change-Id: Iad3430d476abcdad850505ac50e36cd5d5deecb4
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55989
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

util/cbfstool/common.c

@@ -49,7 +49,8 @@ int buffer_create(struct buffer *buffer, size_t size, const char *name)
 	return (buffer->data == NULL);
 }
 
-int buffer_from_file(struct buffer *buffer, const char *filename)
+int buffer_from_file_aligned_size(struct buffer *buffer, const char *filename,
+				  size_t size_granularity)
 {
 	FILE *fp = fopen(filename, "rb");
 	if (!fp) {
@@ -63,20 +64,29 @@ int buffer_from_file(struct buffer *buffer, const char *filename)
 		fclose(fp);
 		return -1;
 	}
-	buffer->size = file_size;
+	buffer->size = ALIGN_UP(file_size, size_granularity);
 	buffer->name = strdup(filename);
 	buffer->data = (char *)malloc(buffer->size);
 	assert(buffer->data);
-	if (fread(buffer->data, 1, buffer->size, fp) != buffer->size) {
+	if (fread(buffer->data, 1, file_size, fp) != (size_t)file_size) {
 		fprintf(stderr, "incomplete read: %s\n", filename);
 		fclose(fp);
 		buffer_delete(buffer);
 		return -1;
 	}
 	fclose(fp);
+
+	if (buffer->size > (size_t)file_size)
+		memset(buffer->data + file_size, 0xff, buffer->size - file_size);
+
 	return 0;
 }
 
+int buffer_from_file(struct buffer *buffer, const char *filename)
+{
+	return buffer_from_file_aligned_size(buffer, filename, 1);
+}
+
 int buffer_write_file(struct buffer *buffer, const char *filename)
 {
 	FILE *fp = fopen(filename, "wb");

util/cbfstool/common.h

@@ -132,6 +132,11 @@ int buffer_create(struct buffer *buffer, size_t size, const char *name);
 /* Loads a file into memory buffer. Returns 0 on success, otherwise non-zero. */
 int buffer_from_file(struct buffer *buffer, const char *filename);
 
+/* Loads a file into memory buffer (with buffer size rounded up to a multiple of
+   size_granularity). Returns 0 on success, otherwise non-zero. */
+int buffer_from_file_aligned_size(struct buffer *buffer, const char *filename,
+				  size_t size_granularity);
+
 /* Writes memory buffer content into file.
  * Returns 0 on success, otherwise non-zero. */
 int buffer_write_file(struct buffer *buffer, const char *filename);