util: detect and warn when using exFAT on MacOS

exFAT is known to cause corruption on MacOS. See bitcoin#28552.

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

src/common/init.cpp

@@ -8,6 +8,7 @@
 #include <logging.h>
 #include <tinyformat.h>
 #include <util/fs.h>
+#include <util/fs_helpers.h>
 #include <util/translation.h>
 
 #include <algorithm>
@@ -62,6 +63,32 @@ std::optional<ConfigError> InitConfig(ArgsManager& args, SettingsAbortFn setting
             fs::create_directories(net_path / "wallets");
         }
 
+        // Warn if we are trying to put the datadir on an exFAT fs on MacOS
+        // This is an upstream issue known to cause bugs, see #28552
+#ifdef __APPLE__
+        struct PathCheck {
+            fs::path path;
+            std::string_view description;
+        };
+        std::array<PathCheck, 2> paths_to_check{{
+            {args.GetDataDirNet(), "data directory"},
+            {args.GetBlocksDirPath(), "blocks directory"}
+        }};
+        for (const auto& check : paths_to_check) {
+            FSType fs_type = GetFilesystemType(check.path);
+            switch(fs_type) {
+                case FSType::EXFAT:
+                    LogWarning("Specified %s \"%s\" is exFAT which is known to have intermittent corruption problems on MacOS.", check.description, fs::PathToString(check.path));
+                    break;
+                case FSType::ERROR:
+                    LogInfo("Failed to detect filesystem type of %s: %s\n", check.description, fs::PathToString(check.path));
+                    break;
+                default:
+                    break;
+            }
+        }
+#endif
+
         // Show an error or warn/log if there is a bitcoin.conf file in the
         // datadir that is being ignored.
         const fs::path base_config_path = base_path / BITCOIN_CONF_FILENAME;

src/util/fs_helpers.cpp

@@ -41,6 +41,10 @@
 #include <shlobj.h> /* For SHGetSpecialFolderPathW */
 #endif // WIN32
 
+#ifdef __APPLE__
+#include <sys/mount.h>
+#endif
+
 /** Mutex to protect dir_locks. */
 static GlobalMutex cs_dir_locks;
 /** A map that contains all the currently held directory locks. After
@@ -309,3 +313,17 @@ std::optional<fs::perms> InterpretPermString(const std::string& s)
         return std::nullopt;
     }
 }
+
+#ifdef __APPLE__
+FSType GetFilesystemType(const fs::path& path) {
+    struct statfs fs_info;
+    if (statfs(path.c_str(), &fs_info) != 0) {
+        return FSType::ERROR;
+    }
+
+    if (strcmp(fs_info.f_fstypename, "exfat") == 0) {
+        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().