xdp-gun: change internal exit statuses of child process, add comments

src/contrib/popenve.c

@@ -67,7 +67,7 @@ dup_stdout:
 			perror("dup_stdout");
 			close(pipefds[0]);
 			close(pipefds[1]);
-			exit(98);
+			exit(EXIT_FAILURE);
 		}
                 close(pipefds[1]);
 
@@ -77,7 +77,7 @@ dup_stdout:
 
                 execve(binfile, args, env);
                 perror("execve");
-                exit(99);
+                exit(EXIT_FAILURE);
         }
 
         close(pipefds[1]);

src/contrib/popenve.h

@@ -25,6 +25,10 @@
  * This function is a safer altervative to popen(), it is the same to
  * popen() as execve() is to system().
  *
+ * Warning: this function is designed to be as simple as possible,
+ *          for reliable operation proper checking for transient
+ *          error is needed.
+ *
  * \param binfile   Executable file to be executed.
  * \param args      NULL-terminated arguments; first shall be the prog name!
  * \param env       NULL-terminated environment variables "key=value"
@@ -38,6 +42,8 @@ int kpopenvef(const char *binfile, char *const args[], char *const env[], bool d
 /*!
  * \brief Variant of kpopenvef() returning FILE*
  *
+ * Warning: the same warning as for kpopenvef() applies here too.
+ *
  * \param binfile   Executable file to be executed.
  * \param args      NULL-terminated arguments; first shall be the prog name!
  * \param env       NULL-terminated environment variables "key=value"