xz: Use pipe2() if available.

configure.ac

@@ -626,8 +626,8 @@ gl_GETOPT
 # Find the best function to set timestamps.
 AC_CHECK_FUNCS([futimens futimes futimesat utimes utime], [break])
 
-# This is nice to have but not mandatory.
-AC_CHECK_FUNCS([posix_fadvise])
+# These are nice to have but not mandatory.
+AC_CHECK_FUNCS([posix_fadvise pipe2])
 
 TUKLIB_PROGNAME
 TUKLIB_INTEGER

src/xz/file_io.c

@@ -82,7 +82,13 @@ io_init(void)
 	// we are root.
 	warn_fchown = geteuid() == 0;
 
-	// Create a pipe for the self-pipe trick.
+	// Create a pipe for the self-pipe trick. If pipe2() is available,
+	// we can avoid the fcntl() calls.
+#	ifdef HAVE_PIPE2
+	if (pipe2(user_abort_pipe, O_NONBLOCK))
+		message_fatal(_("Error creating a pipe: %s"),
+				strerror(errno));
+#	else
 	if (pipe(user_abort_pipe))
 		message_fatal(_("Error creating a pipe: %s"),
 				strerror(errno));
@@ -96,6 +102,7 @@ io_init(void)
 					strerror(errno));
 	}
 #	endif
+#endif
 
 #ifdef __DJGPP__
 	// Avoid doing useless things when statting files.