Only read the FIT header when possible to speed up reading attributes.

fdtextract.c

 /*
- * dumpimage -- Tool to extract sub images from FIT image.
+ * fdtextract -- Tool to extract sub images from FIT image.
  *
  * Copyright (C) 2021 IOPSYS Software Solutions AB. All rights reserved.
  *
@@ -89,12 +89,19 @@ static int list_images(char *buf)
 }
 
 /* Extract an image embedded in the FIT. */
-static int extract_image(char *buf, char *name, char *out)
+static int extract_image(const char *file, char *name, char *out)
 {
 	char path[MAX_PATH_LEN];
 	int noffset, fd, count;
 	unsigned int data_size, data_offset;
 	const fdt32_t *val;
+	char *buf;
+	size_t len;
+
+	buf = utilfdt_read(file, &len);
+	if (!buf) {
+		die("could not read: %s\n", file);
+	}
 
 	snprintf(path, MAX_PATH_LEN, "/images/%s", name);
 	noffset = fdt_path_offset(buf, path);
@@ -205,6 +212,38 @@ static int get_attribute(char *buf, char *name)
 	return 0;
 }
 
+char *read_header(const char *file)
+{
+	char *buf;
+	int fd, total_size;
+	size_t len;
+
+	fd = open(file, O_RDONLY);
+	if (fd < 0)
+        return NULL;
+
+	/* Read minimal static struct */
+	buf = malloc(FDT_V1_SIZE);
+	if (!buf)
+		return NULL;
+
+	len = read(fd, buf, FDT_V1_SIZE);
+	if (len < FDT_V1_SIZE)
+		return NULL;
+
+	/* Read rest of header */
+	total_size = fdt_totalsize(buf);
+	buf = realloc(buf, total_size);
+	if (!buf)
+		return NULL;
+
+	len = read(fd, buf + FDT_V1_SIZE, total_size - FDT_V1_SIZE);
+	if (len < total_size - FDT_V1_SIZE)
+		return NULL;
+
+	return buf;
+}
+
 int main(int argc, char *argv[])
 {
 	const char *file;
@@ -212,7 +251,6 @@ int main(int argc, char *argv[])
 	char *buf, *name = NULL, *out = NULL;
 	bool list = false, extract = false,
 		hash = false, attribute = false;
-	size_t len;
 
     while ((opt = util_getopt_long()) != EOF) {
         switch (opt) {
@@ -242,26 +280,28 @@ int main(int argc, char *argv[])
         usage("missing input filename");
     file = argv[optind];
 
-    buf = utilfdt_read(file, &len);
+    buf = read_header(file);
     if (!buf) {
-        die("could not read: %s\n", file);
+        die("could not read header from: %s\n", file);
 	}
 
 	if (fdt_check_header(buf)) {
 		die("Bad header in %s\n", file);
 	}
 
+	/* Pass the pointer to the header to read attributes. */
 	if (list)
 		ret = list_images(buf);
 
-	if (extract)
-		ret = extract_image(buf, name, out);
-
 	if (hash)
 		ret = get_hash(buf, name);
 
 	if (attribute)
 		ret = get_attribute(buf, name);
 
+	/* Let extract image read the entire file. */
+	if (extract)
+		ret = extract_image(file, name, out);
+
 	return ret;
 }