fix: feature-detect fuse_file_info.parallel_direct_writes

The field appeared in libfuse 3.15, not 3.14 as the version check
assumed (ubuntu-24.04 ships 3.14 and failed to build). Detect the
struct member in configure instead of comparing version numbers.

Author: matejk

configure.ac

@@ -319,6 +319,22 @@ then
 else
     AC_MSG_RESULT([3])
 fi
+
+dnl
+dnl struct fuse_file_info.parallel_direct_writes appeared in libfuse 3.15;
+dnl detect the member instead of relying on version numbers.
+dnl
+if test "x${with_fuse2}" != "xyes"
+then
+    SAVE_CFLAGS=$CFLAGS
+    CFLAGS="$CFLAGS ${FUSE_MODULE_CFLAGS} -DFUSE_USE_VERSION=31"
+    AC_CHECK_MEMBER([struct fuse_file_info.parallel_direct_writes],
+        [AC_DEFINE([HAVE_FUSE_PARALLEL_DIRECT_WRITES], [1],
+            [Define to 1 if struct fuse_file_info has parallel_direct_writes])],
+        [],
+        [[#include <fuse.h>]])
+    CFLAGS="$SAVE_CFLAGS"
+fi
 PKG_CHECK_MODULES([LIBXML2_MODULE], [libxml-2.0 >= 2.6.16])
 
 if test "x${host_mac}" = "xyes"

src/ltfs_fuse.c

@@ -117,7 +117,7 @@ static void _ltfs_fuse_set_cache_flags(struct fuse_file_info *fi, struct ltfs_fu
 	if (priv->direct_io) {
 		fi->direct_io = 1;
 		fi->keep_cache = 0;
-#if defined(HAVE_FUSE3) && FUSE_VERSION >= FUSE_MAKE_VERSION(3, 14)
+#ifdef HAVE_FUSE_PARALLEL_DIRECT_WRITES
 		/* Writes are serialized further down; this only removes the
 		 * kernel-side exclusive lock for non-extending direct writes. */
 		fi->parallel_direct_writes = 1;