diff --git a/usr.sbin/bhyve/qemu_fwcfg.h b/usr.sbin/bhyve/qemu_fwcfg.h
--- a/usr.sbin/bhyve/qemu_fwcfg.h
+++ b/usr.sbin/bhyve/qemu_fwcfg.h
@@ -18,4 +18,6 @@
 	uint8_t *data;
 };
 
+int qemu_fwcfg_add_file(const uint8_t name[QEMU_FWCFG_MAX_NAME],
+    const uint32_t size, void *const data);
 int qemu_fwcfg_init(struct vmctx *const ctx);
diff --git a/usr.sbin/bhyve/qemu_fwcfg.c b/usr.sbin/bhyve/qemu_fwcfg.c
--- a/usr.sbin/bhyve/qemu_fwcfg.c
+++ b/usr.sbin/bhyve/qemu_fwcfg.c
@@ -43,6 +43,8 @@
 #define QEMU_FWCFG_INDEX_ID 0x01
 #define QEMU_FWCFG_INDEX_FILE_DIR 0x19
 
+#define QEMU_FWCFG_FIRST_FILE_INDEX 0x20
+
 #define QEMU_FWCFG_MIN_FILES 10
 
 #pragma pack(1)
@@ -87,6 +89,7 @@
 	union qemu_fwcfg_selector selector;
 	struct qemu_fwcfg_item items[QEMU_FWCFG_MAX_ARCHS]
 				    [QEMU_FWCFG_MAX_ENTRIES];
+	struct qemu_fwcfg_directory *directory;
 };
 
 static struct qemu_fwcfg_softc fwcfg_sc;
@@ -256,6 +259,93 @@
 	return (register_inout(&iop));
 }
 
+int
+qemu_fwcfg_add_file(const uint8_t name[QEMU_FWCFG_MAX_NAME],
+    const uint32_t size, void *const data)
+{
+	/*
+	 * QEMU specifies count as big endian.
+	 * Convert it to host endian to work with it.
+	 */
+	const uint32_t count = be32toh(fwcfg_sc.directory->be_count) + 1;
+
+	/* add file to items list */
+	const uint32_t index = QEMU_FWCFG_FIRST_FILE_INDEX + count - 1;
+	const int error = qemu_fwcfg_add_item(QEMU_FWCFG_ARCHITECTURE_GENERIC,
+	    index, size, data);
+	if (error != 0) {
+		return (error);
+	}
+
+	/*
+	 * files should be sorted alphabetical, get index for new file
+	 */
+	uint32_t file_index;
+	for (file_index = 0; file_index < count - 1; ++file_index) {
+		if (strcmp(name, fwcfg_sc.directory->files[file_index].name) <
+		    0)
+			break;
+	}
+
+	if (count > QEMU_FWCFG_MIN_FILES) {
+		/* alloc new file directory */
+		const uint64_t new_size = sizeof(struct qemu_fwcfg_directory) +
+		    count * sizeof(struct qemu_fwcfg_file);
+		struct qemu_fwcfg_directory *const new_directory = calloc(1,
+		    new_size);
+		if (new_directory == NULL) {
+			warnx(
+			    "%s: Unable to allocate a new qemu fwcfg files directory (count %d)",
+			    __func__, count);
+			return (-ENOMEM);
+		}
+
+		/* copy files below file_index to new directory */
+		memcpy(new_directory->files, fwcfg_sc.directory->files,
+		    file_index * sizeof(struct qemu_fwcfg_file));
+
+		/* copy files above file_index to directory */
+		memcpy(&new_directory->files[file_index + 1],
+		    &fwcfg_sc.directory->files[file_index],
+		    (count - file_index) * sizeof(struct qemu_fwcfg_file));
+
+		/* free old directory */
+		free(fwcfg_sc.directory);
+
+		/* set directory pointer to new directory */
+		fwcfg_sc.directory = new_directory;
+
+		/* adjust directory pointer */
+		fwcfg_sc.items[0][QEMU_FWCFG_INDEX_FILE_DIR].data =
+		    (uint8_t *)fwcfg_sc.directory;
+	} else {
+		/* shift files behind file_index */
+		for (uint32_t i = QEMU_FWCFG_MIN_FILES - 1; i > file_index;
+		     --i) {
+			memcpy(&fwcfg_sc.directory->files[i],
+			    &fwcfg_sc.directory->files[i - 1],
+			    sizeof(struct qemu_fwcfg_file));
+		}
+	}
+
+	/*
+	 * QEMU specifies count, size and index as big endian.
+	 * Save these values in big endian to simplify guest reads of these
+	 * values.
+	 */
+	fwcfg_sc.directory->be_count = htobe32(count);
+	fwcfg_sc.directory->files[file_index].be_size = htobe32(size);
+	fwcfg_sc.directory->files[file_index].be_selector = htobe16(index);
+	strcpy(fwcfg_sc.directory->files[file_index].name, name);
+
+	/* set new size for the fwcfg_file_directory */
+	fwcfg_sc.items[0][QEMU_FWCFG_INDEX_FILE_DIR].size =
+	    sizeof(struct qemu_fwcfg_directory) +
+	    count * sizeof(struct qemu_fwcfg_file);
+
+	return (0);
+}
+
 int
 qemu_fwcfg_init(struct vmctx *const ctx)
 {