Libguestfs - Mar 2023 - [libnbd PATCH v4 2/3] lib/utils: add async-signal-safe assert()

Add an assert() variant that we may call between fork() and exec*().

Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---

Notes:
    v4:
    
    - rework with xwritel()
    
    - do not pick up R-b tags due to the above
    
    context:-U13

 lib/internal.h | 13 +++++++++++++
 lib/utils.c    | 16 ++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/lib/internal.h b/lib/internal.h
index 73d243a13743..4e75f97d2a8a 100644
--- a/lib/internal.h
+++ b/lib/internal.h
@@ -517,14 +517,27 @@ extern char *nbd_internal_printable_string (const char
*str)
 extern char *nbd_internal_printable_string_list (char **list)
   LIBNBD_ATTRIBUTE_ALLOC_DEALLOC (free);
 
 /* These are wrappers around socket(2) and socketpair(2).  They
  * always set SOCK_CLOEXEC.  nbd_internal_socket can set SOCK_NONBLOCK
  * according to the nonblock parameter.
  */
 extern int nbd_internal_socket (int domain, int type, int protocol,
                                 bool nonblock);
 extern int nbd_internal_socketpair (int domain, int type, int protocol,
                                     int *fds)
   LIBNBD_ATTRIBUTE_NONNULL (4);
 
+extern void nbd_internal_fork_safe_assert (int result, const char *file,
+                                           long line, const char *func,
+                                           const char *assertion)
+  LIBNBD_ATTRIBUTE_NONNULL (2, 4, 5);
+
+#ifdef NDEBUG
+#define NBD_INTERNAL_FORK_SAFE_ASSERT(expression) ((void)0)
+#else
+#define NBD_INTERNAL_FORK_SAFE_ASSERT(expression)                        \
+  (nbd_internal_fork_safe_assert ((expression) != 0, __FILE__, __LINE__, \
+                                  __func__, #expression))
+#endif
+
 #endif /* LIBNBD_INTERNAL_H */
diff --git a/lib/utils.c b/lib/utils.c
index 62b4bfdda5c3..255f428dd8b6 100644
--- a/lib/utils.c
+++ b/lib/utils.c
@@ -479,13 +479,29 @@ nbd_internal_socketpair (int domain, int type, int
protocol, int *fds)
   if (ret == 0) {
     for (i = 0; i < 2; i++) {
       if (fcntl (fds[i], F_SETFD, FD_CLOEXEC) == -1) {
         close (fds[0]);
         close (fds[1]);
         return -1;
       }
     }
   }
 #endif
 
   return ret;
 }
+
+void
+nbd_internal_fork_safe_assert (int result, const char *file, long line,
+                               const char *func, const char *assertion)
+{
+  const char *line_out;
+  char line_buf[32];
+
+  if (result)
+    return;
+
+  line_out = nbd_internal_fork_safe_itoa (line, line_buf, sizeof line_buf);
+  xwritel (STDERR_FILENO, file, ":", line_out, ": ", func,
": Assertion `",
+           assertion, "' failed.\n", (char *)NULL);
+  abort ();
+}

On Wed, Mar 15, 2023 at 12:01:56PM +0100, Laszlo Ersek
wrote:
> Add an assert() variant that we may call between fork() and exec*().
> 
> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
> ---
> 
> +void
> +nbd_internal_fork_safe_assert (int result, const char *file, long line,
> +                               const char *func, const char *assertion)
> +{
> +  const char *line_out;
> +  char line_buf[32];
> +
> +  if (result)
> +    return;
> +
> +  line_out = nbd_internal_fork_safe_itoa (line, line_buf, sizeof
line_buf);
> +  xwritel (STDERR_FILENO, file, ":", line_out, ": ",
func, ": Assertion `",
> +           assertion, "' failed.\n", (char *)NULL);
xwritel() makes this so much shorter ;)

Reviewed-by: Eric Blake <eblake at redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org