linux: Fix sys/mount.h usage with kernel headers

Now that kernel exports linux/mount.h and includes it on linux/fs.h,
its definitions might clash with glibc exports sys/mount.h.  To avoid
the need to rearrange the Linux header to be always after glibc one,
the glibc sys/mount.h is changed to:

  1. Undefine the macros also used as enum constants.  This covers prior
     inclusion of <linux/mount.h> (for instance MS_RDONLY).

  2. Include <linux/mount.h> based on the usual __has_include check
     (needs to use __has_include ("linux/mount.h") to paper over GCC
     bugs.

  3. Define enum fsconfig_command only if FSOPEN_CLOEXEC is not defined.
     (FSOPEN_CLOEXEC should be a very close proxy.)

  4. Define struct mount_attr if MOUNT_ATTR_SIZE_VER0 is not defined.
     (Added in the same commit on the Linux side.)

This patch also adds some tests to check if including linux/fs.h and
linux/mount.h after and before sys/mount.h does work.

Checked on x86_64-linux-gnu.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

1 files changed, 66 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/tst-mount-compile.py b/sysdeps/unix/sysv/linux/tst-mount-compile.py
new file mode 100755
index 0000000..0ec74d4
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-mount-compile.py
@@ -0,0 +1,66 @@
+#!/usr/bin/python3
+# Check if glibc provided sys/mount.h can be used along related kernel
+# headers.
+# Copyright (C) 2022 Free Software Foundation, Inc.
+# This file is part of the GNU C Library.
+#
+# The GNU C Library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# The GNU C Library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with the GNU C Library; if not, see
+# <https://www.gnu.org/licenses/>.
+
+import argparse
+import sys
+
+import glibcextract
+
+
+def main():
+    """The main entry point."""
+    parser = argparse.ArgumentParser(
+        description='Check if glibc provided sys/mount.h can be '
+                    ' used along related kernel headers.')
+    parser.add_argument('--cc', metavar='CC',
+                        help='C compiler (including options) to use')
+    args = parser.parse_args()
+
+    if glibcextract.compile_c_snippet(
+            '#include <linux/mount.h>',
+            args.cc).returncode != 0:
+        sys.exit (77)
+
+    def check(testname, snippet):
+        # Add -Werror to catch macro redefinitions and _ISOMAC to avoid
+        # internal glibc definitions.
+        r = glibcextract.compile_c_snippet(snippet, args.cc,
+                '-Werror -D_ISOMAC')
+        if r.returncode != 0:
+            print('error: test {}:\n{}'.format(testname, r.output.decode()))
+        return r.returncode
+
+    status = max(
+        check("sys/mount.h + linux/mount.h",
+              "#include <sys/mount.h>\n"
+              "#include <linux/mount.h>"),
+        check("sys/mount.h + linux/fs.h",
+              "#include <sys/mount.h>\n"
+              "#include <linux/fs.h>"),
+        check("linux/mount.h + sys/mount.h",
+              "#include <linux/mount.h>\n"
+              "#include <sys/mount.h>"),
+        check("linux/fs.h + sys/mount.h",
+              "#include <linux/fs.h>\n"
+              "#include <sys/mount.h>"))
+    sys.exit(status)
+
+if __name__ == '__main__':
+    main()