+static int spawn_prog(const char *pgm, const char **arg)
+{
+ pid_t pid;
+ int status;
+
+ fflush(NULL);
+ pid = fork();
+ if (pid < 0)
+ die("unable to fork");
+ if (!pid) {
+ execvp(pgm, (char *const*) arg);
+ exit(255);
+ }
+
+ while (waitpid(pid, &status, 0) < 0) {
+ if (errno == EINTR)
+ continue;
+ return -1;
+ }
+
+ /* Earlier we did not check the exit status because
+ * diff exits non-zero if files are different, and
+ * we are not interested in knowing that. It was a
+ * mistake which made it harder to quit a diff-*
+ * session that uses the git-apply-patch-script as
+ * the GIT_EXTERNAL_DIFF. A custom GIT_EXTERNAL_DIFF
+ * should also exit non-zero only when it wants to
+ * abort the entire diff-* session.
+ */
+ if (WIFEXITED(status) && !WEXITSTATUS(status))
+ return 0;
+ return -1;
+}
+