[PATCH] src/locktest.c: fix build failure of struct delegation

[Zorro Lang <zlang@kernel.org>]

Since glibc commit f2e3dacbff88 ("Add new constants from Linux 6.12,
6.18 and 6.19 to bits/fcntl-linux.h"), the F_GETDELEG and F_SETDELEG
constants from Linux 6.19 have been added directly into <fcntl.h>.
However, the corresponding full definition for 'struct delegation'
was not included in glibc's userspace wrapper. That causes below
build error:

 locktest.c:1065:16: error: variable 'deleg' has initializer but incomplete type
  1065 |         struct delegation deleg = { .d_type = F_UNLCK };
 ...

Fix this by isolating the definition of 'struct delegation' from the
command macros via autoconf capability probing:

1. Add an AC_CHECK_TYPES check for 'struct delegation' in configure.ac.
2. In locktest.c, unbind 'struct delegation' from the '#ifndef F_GETDELEG'
   guard and wrap it with '#ifndef HAVE_STRUCT_DELEGATION' instead.

Signed-off-by: Zorro Lang <zlang@kernel.org>
---

Hi,

fstests currently fails to build against the latest glibc, with the root
cause detailed in the commit log above.

The glibc now defines F_GETDELEG and F_SETDELEG, but leaves out the actual
'struct delegation' definition. The complete struct is available in <linux/fcntl.h>,
but we cannot simply include both <fcntl.h> and <linux/fcntl.h> due to nasty
namespace redefinition conflicts.

I am not entirely sure if glibc will bring in 'struct delegation', so for now,
I chose to decouple and handle the structure definition independently via
autoconf.

Any thoughts or better suggestions on how we should handle this transition?

Thanks,
Zorro

 configure.ac   | 4 ++++
 src/locktest.c | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/configure.ac b/configure.ac
index feb24ddd..6d7ff3ba 100644
--- a/configure.ac
+++ b/configure.ac
@@ -111,6 +111,10 @@ AC_CHECK_TYPES([struct btrfs_ioctl_received_subvol_args], [], [], [[
 #include <stddef.h>
 #include <linux/btrfs.h>
 ]])
+AC_CHECK_TYPES([struct delegation], [], [], [[
+#include <stddef.h>
+#include <fcntl.h>
+]])
 AC_CHECK_HEADERS([linux/btrfs.h linux/btrfs_tree.h])
 AC_CHECK_MEMBERS([struct btrfs_ioctl_vol_args_v2.subvolid], [], [], [[
 #include <stddef.h>
diff --git a/src/locktest.c b/src/locktest.c
index 54ee1f07..d0264c94 100644
--- a/src/locktest.c
+++ b/src/locktest.c
@@ -80,7 +80,9 @@ extern int h_errno;
 #ifndef F_GETDELEG
 #define F_GETDELEG	(1024 + 15)
 #define F_SETDELEG	(1024 + 16)
+#endif
 
+#ifndef HAVE_STRUCT_DELEGATION
 struct delegation {
 	uint32_t d_flags;
 	uint16_t d_type;
-- 
2.55.0