libpayload: bring in file attribute support from cbfstool

This comes from cbfstool (GPL) into libpayload (BSD-l), but I could have
just as well written it in libpayload first.

Change-Id: I86baefe5c299125a4733fa20523efd5d06de7182
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-on: http://review.coreboot.org/11675
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

payloads/libpayload/include/cbfs_core.h

@@ -132,10 +132,34 @@ struct cbfs_file {
 	char magic[8];
 	uint32_t len;
 	uint32_t type;
-	uint32_t checksum;
+	uint32_t attributes_offset;
 	uint32_t offset;
+	char filename[];
 } __attribute__((packed));
 
+/* Depending on how the header was initialized, it may be backed with 0x00 or
+ * 0xff. Support both. */
+#define CBFS_FILE_ATTR_TAG_UNUSED 0
+#define CBFS_FILE_ATTR_TAG_UNUSED2 0xffffffff
+
+/* The common fields of extended cbfs file attributes.
+   Attributes are expected to start with tag/len, then append their
+   specific fields. */
+struct cbfs_file_attribute {
+	uint32_t tag;
+	/* len covers the whole structure, incl. tag and len */
+	uint32_t len;
+	uint8_t data[0];
+} __attribute__((packed));
+
+/* Given a cbfs_file, return the first file attribute, or NULL. */
+struct cbfs_file_attribute *cbfs_file_first_attr(struct cbfs_file *file);
+
+/* Given a cbfs_file and a cbfs_file_attribute, return the attribute that
+ * follows it, or NULL. */
+struct cbfs_file_attribute *cbfs_file_next_attr(struct cbfs_file *file,
+	struct cbfs_file_attribute *attr);
+
 /*** Component sub-headers ***/
 
 /* Following are component sub-headers for the "standard"

payloads/libpayload/libcbfs/cbfs_core.c

@@ -213,6 +213,47 @@ void *cbfs_get_file_content(struct cbfs_media *media, const char *name,
 	return (void *)CBFS_SUBHEADER(file);
 }
 
+struct cbfs_file_attribute *cbfs_file_first_attr(struct cbfs_file *file)
+{
+	/* attributes_offset should be 0 when there is no attribute, but all
+	 * values that point into the cbfs_file header are invalid, too. */
+	if (ntohl(file->attributes_offset) <= sizeof(*file))
+		return NULL;
+
+	/* There needs to be enough space for the file header and one
+	 * attribute header for this to make sense. */
+	if (ntohl(file->offset) <=
+		sizeof(*file) + sizeof(struct cbfs_file_attribute))
+		return NULL;
+
+	return (struct cbfs_file_attribute *)
+		(((uint8_t *)file) + ntohl(file->attributes_offset));
+}
+
+struct cbfs_file_attribute *cbfs_file_next_attr(struct cbfs_file *file,
+	struct cbfs_file_attribute *attr)
+{
+	/* ex falso sequitur quodlibet */
+	if (attr == NULL)
+		return NULL;
+
+	/* Is there enough space for another attribute? */
+	if ((uint8_t *)attr + ntohl(attr->len) +
+		sizeof(struct cbfs_file_attribute) >=
+		(uint8_t *)file + ntohl(file->offset))
+		return NULL;
+
+	struct cbfs_file_attribute *next = (struct cbfs_file_attribute *)
+		(((uint8_t *)attr) + ntohl(attr->len));
+	/* If any, "unused" attributes must come last. */
+	if (ntohl(next->tag) == CBFS_FILE_ATTR_TAG_UNUSED)
+		return NULL;
+	if (ntohl(next->tag) == CBFS_FILE_ATTR_TAG_UNUSED2)
+		return NULL;
+
+	return next;
+}
+
 int cbfs_decompress(int algo, void *src, void *dst, int len)
 {
 	switch (algo) {