util: detect and warn when using exFAT on macOS

exFAT is known to cause corruption on macOS. See #28552.

Therefore we should warn when using this fs format for either the blocks
or data directories on macOS.

Co-authored-by: l0rinc <pap.lorinc@gmail.com>

src/util/fs_helpers.cpp

@@ -30,6 +30,11 @@
 #include <shlobj.h>
 #endif // WIN32
 
+#ifdef __APPLE__
+#include <sys/mount.h>
+#include <sys/param.h>
+#endif
+
 /** Mutex to protect dir_locks. */
 static GlobalMutex cs_dir_locks;
 /** A map that contains all the currently held directory locks. After
@@ -298,3 +303,15 @@ std::optional<fs::perms> InterpretPermString(const std::string& s)
         return std::nullopt;
     }
 }
+
+#ifdef __APPLE__
+FSType GetFilesystemType(const fs::path& path)
+{
+    if (struct statfs fs_info; statfs(path.c_str(), &fs_info)) {
+        return FSType::ERROR;
+    } else if (std::string_view{fs_info.f_fstypename} == "exfat") {
+        return FSType::EXFAT;
+    }
+    return FSType::OTHER;
+}
+#endif

src/util/fs_helpers.h

@@ -14,6 +14,23 @@
 #include <limits>
 #include <optional>
 
+#ifdef __APPLE__
+enum class FSType {
+    EXFAT,
+    OTHER,
+    ERROR
+};
+
+/**
+ * Detect filesystem type for a given path.
+ * Currently identifies exFAT filesystems which cause issues on macOS.
+ *
+ * @param[in] path The directory path to check
+ * @return FSType enum indicating the filesystem type
+ */
+FSType GetFilesystemType(const fs::path& path);
+#endif
+
 /**
  * Ensure file contents are fully committed to disk, using a platform-specific
  * feature analogous to fsync().