Factor out read_firmware_device()

lib/chromeos/load_firmware_fw.c

Index: lib/chromeos/load_firmware_fw.c
diff --git a/lib/chromeos/load_firmware_fw.c b/lib/chromeos/load_firmware_fw.c
index b5d271bd7aa71f0b829c73543c2000011ea93a6e..18d2e34141fa022d427dbea4c05bc0c0aeafd85e 100644
--- a/lib/chromeos/load_firmware_fw.c
+++ b/lib/chromeos/load_firmware_fw.c
@@ -37,6 +37,36 @@ void GetFirmwareBody_dispose(firmware_storage_t *f)
 			free(f->firmware_body[i]);
 }
 
+int read_firmware_device(firmware_storage_t *file, off_t offset, void *buf,
+		size_t count)
+{
+	ssize_t size;
+
+	if (file->seek(file->context, offset, SEEK_SET) < 0) {
+		debug(PREFIX "seek to address 0x%08x fail\n", offset);
+		return -1;
+	}
+
+	size = 0;
+	while (count > 0 &&
+			(size = file->read(file->context, buf, count)) > 0) {
+		count -= size;
+		buf += size;
+	}
+
+	if (size < 0) {
+		debug(PREFIX "an error occur when read firmware: %d\n", size);
+		return -1;
+	}
+
+	if (count > 0) {
+		debug(PREFIX "cannot read all data: %d\n", count);
+		return -1;
+	}
+
+	return 0;
+}
+
 /*
  * See vboot_reference/firmware/include/load_firmware_fw.h for documentation of
  * this function.