extern void guestfs_set_subprocess_quit_callback (guestfs_h *g, guestfs_subprocess_quit_cb cb, void *opaque);
extern void guestfs_set_launch_done_callback (guestfs_h *g, guestfs_launch_done_cb cb, void *opaque);
-extern void guestfs_error (guestfs_h *g, const char *fs, ...);
-extern void guestfs_perrorf (guestfs_h *g, const char *fs, ...);
+extern void guestfs_error (guestfs_h *g, const char *fs, ...)
+ __attribute__((format (printf,2,3)));
+extern void guestfs_perrorf (guestfs_h *g, const char *fs, ...)
+ __attribute__((format (printf,2,3)));
extern void *guestfs_safe_malloc (guestfs_h *g, size_t nbytes);
extern void *guestfs_safe_realloc (guestfs_h *g, void *ptr, int nbytes);
extern char *guestfs_safe_strdup (guestfs_h *g, const char *str);