util: use F_DUPFD_QUERY on Linux

F_DUPFD_QUERY has been introduced in 6.10 exactly for the purpose
of telling if 2 fd points at the same file description so use it
first.

If it's not supported, we'll get r=-1 and errno=EINVAL, and we can
fallback on KCMP or epoll.

Acked-by: Simona Vetter <simona.vetter@ffwll.ch>
Acked-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34447>

src/util/os_file.c

@@ -29,6 +29,9 @@
 #ifndef F_DUPFD_CLOEXEC
 #define F_DUPFD_CLOEXEC 1030
 #endif
+#ifndef F_DUPFD_QUERY
+#define F_DUPFD_QUERY 1027
+#endif
 #endif
 
 
@@ -240,6 +243,18 @@ os_same_file_description(int fd1, int fd2)
    if (fd1 == fd2)
       return 0;
 
+#if DETECT_OS_LINUX
+   /* Use F_DUPFD_QUERY if available. */
+   int r = fcntl(fd1, F_DUPFD_QUERY, fd2);
+
+   if (r < 0) {
+      if (errno == EBADF)
+         return 1;
+   } else {
+      return r == 1 ? 0 : 1;
+   }
+#endif
+
 #ifdef SYS_kcmp
    return syscall(SYS_kcmp, pid, pid, KCMP_FILE, fd1, fd2);
 #elif DETECT_OS_DRAGONFLY || DETECT_OS_FREEBSD
@@ -269,8 +284,6 @@ os_same_file_description(int fd1, int fd2)
 
    return (fd1_kfile < fd2_kfile) | ((fd1_kfile > fd2_kfile) << 1);
 #elif DETECT_OS_LINUX
-   int r;
-
    int efd = epoll_create1(EPOLL_CLOEXEC);
    if (efd < 0)
       return -1;