shared: introduce os_fd_clear_cloexec()

This function will be used between fork() and exec() to remove the
close-on-exec flag. The first user will be compositor/xwayland.c.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

shared/os-compatibility.c

@@ -40,6 +40,21 @@
 
 #define READONLY_SEALS (F_SEAL_SHRINK | F_SEAL_GROW | F_SEAL_WRITE)
 
+int
+os_fd_clear_cloexec(int fd)
+{
+	int flags;
+
+	flags = fcntl(fd, F_GETFD);
+	if (flags == -1)
+		return -1;
+
+	if (fcntl(fd, F_SETFD, flags & ~(int)FD_CLOEXEC) == -1)
+		return -1;
+
+	return 0;
+}
+
 int
 os_fd_set_cloexec(int fd)
 {

shared/os-compatibility.h

@@ -30,6 +30,9 @@
 
 #include <sys/types.h>
 
+int
+os_fd_clear_cloexec(int fd);
+
 int
 os_fd_set_cloexec(int fd);