basic: introduce our own sys/mount.h implementation

To resolve conflict with sys/mount.h and linux/mount.h or linux/fs.h.

The conflict between sys/mount.h and linux/mount.h is resolved in
glibc-2.37 (774058d72942249f71d74e7f2b639f77184160a6), but our baseline
is still glibc-2.31. Also, even with the version or newer, still
sys/mount.h conflicts with linux/fs.h, which is included by
linux/btrfs.h.

This introduces our own implementation of sys/mount.h, that can be
simultaneously included with linux/mount.h and linux/fs.h. This also
imports linux/fs.h, linux/mount.h, and several other dependent headers.
The introduced sys/mount.h header itself may not be enough simple, but
by using the header, we can drop most of workarounds in other source files.

src/basic/sys/mount.h

@@ -0,0 +1,115 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include <features.h>
+#include <stdint.h>
+#include <stddef.h>
+#include <sys/ioctl.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include "missing_fcntl.h"
+#include "missing_fs.h"
+#include "missing_syscall_def.h"
+
+/* Possible value for FLAGS parameter of `umount2'.  */
+enum
+{
+        MNT_FORCE = 1,                /* Force unmounting.  */
+#define MNT_FORCE MNT_FORCE
+        MNT_DETACH = 2,               /* Just detach from the tree.  */
+#define MNT_DETACH MNT_DETACH
+        MNT_EXPIRE = 4,               /* Mark for expiry.  */
+#define MNT_EXPIRE MNT_EXPIRE
+        UMOUNT_NOFOLLOW = 8           /* Don't follow symlink on umount.  */
+#define UMOUNT_NOFOLLOW UMOUNT_NOFOLLOW
+};
+
+/* Mount a filesystem.  */
+extern int mount(const char *__special_file, const char *__dir, const char *__fstype, unsigned long int __rwflag, const void *__data) __THROW;
+
+/* Unmount a filesystem.  */
+extern int umount(const char *__special_file) __THROW;
+
+/* Unmount a filesystem.  Force unmounting if FLAGS is set to MNT_FORCE.  */
+extern int umount2(const char *__special_file, int __flags) __THROW;
+
+/* Open the filesystem referenced by FS_NAME so it can be configured for
+   mouting.  */
+#if HAVE_FSOPEN
+extern int fsopen(const char *__fs_name, unsigned int __flags) __THROW;
+#else
+static inline int missing_fsopen(const char *fsname, unsigned flags) {
+        return syscall(__NR_fsopen, fsname, flags);
+}
+#  define fsopen missing_fsopen
+#endif
+
+/* Create a mount representation for the FD created by fsopen using
+   FLAGS with ATTR_FLAGS describing how the mount is to be performed.  */
+#if HAVE_FSMOUNT
+extern int fsmount(int __fd, unsigned int __flags, unsigned int __ms_flags) __THROW;
+#else
+static inline int missing_fsmount(int fd, unsigned flags, unsigned ms_flags) {
+        return syscall(__NR_fsmount, fd, flags, ms_flags);
+}
+#  define fsmount missing_fsmount
+#endif
+
+/* Add the mounted FROM_DFD referenced by FROM_PATHNAME filesystem returned
+   by fsmount in the hierarchy in the place TO_DFD reference by TO_PATHNAME
+   using FLAGS.  */
+#if HAVE_MOVE_MOUNT
+extern int move_mount(int __from_dfd, const char *__from_pathname, int __to_dfd, const char *__to_pathname, unsigned int flags) __THROW;
+#else
+static inline int missing_move_mount(
+                int from_dfd,
+                const char *from_pathname,
+                int to_dfd,
+                const char *to_pathname,
+                unsigned flags) {
+
+        return syscall(__NR_move_mount, from_dfd, from_pathname, to_dfd, to_pathname, flags);
+}
+#  define move_mount missing_move_mount
+#endif
+
+/* Set parameters and trigger CMD action on the FD context.  KEY, VALUE,
+   and AUX are used depending ng of the CMD.  */
+#if HAVE_FSCONFIG
+extern int fsconfig(int __fd, unsigned int __cmd, const char *__key, const void *__value, int __aux) __THROW;
+#else
+static inline int missing_fsconfig(int fd, unsigned cmd, const char *key, const void *value, int aux) {
+        return syscall(__NR_fsconfig, fd, cmd, key, value, aux);
+}
+#  define fsconfig missing_fsconfig
+#endif
+
+/* Equivalent of fopen for an existing mount point.  */
+#if HAVE_FSPICK
+extern int fspick(int __dfd, const char *__path, unsigned int __flags) __THROW;
+#endif
+
+/* Open the mount point FILENAME in directory DFD using FLAGS.  */
+#if HAVE_OPEN_TREE
+extern int open_tree(int __dfd, const char *__filename, unsigned int __flags) __THROW;
+#else
+static inline int missing_open_tree(int dfd, const char *filename, unsigned flags) {
+        return syscall(__NR_open_tree, dfd, filename, flags);
+}
+#  define open_tree missing_open_tree
+#endif
+
+/* Change the mount properties of the mount or an entire mount tree.  If
+   PATH is a relative pathname, then it is interpreted relative to the
+   directory referred to by the file descriptor dirfd.  Otherwise if DFD is
+   the special value AT_FDCWD then PATH is interpreted relative to the current
+   working directory of the calling process.  */
+#if HAVE_MOUNT_SETATTR
+extern int mount_setattr(int __dfd, const char *__path, unsigned int __flags, struct mount_attr *__uattr, size_t __usize) __THROW;
+#else
+static inline int missing_mount_setattr(int dfd, const char *path, unsigned flags, struct mount_attr *attr, size_t size) {
+        return syscall(__NR_mount_setattr, dfd, path, flags, attr, size);
+}
+#  define mount_setattr missing_mount_setattr
+#endif