From 6177090eca2f48b25d8f48b2c994f946c040f599 Mon Sep 17 00:00:00 2001
From: Marcus Holland-Moritz <github@mhxnet.de>
Date: Wed, 9 Aug 2023 18:32:46 +0200
Subject: [PATCH] Don't enable `readlink` if filesystem has no symlinks

This reduces the number of `getattr` calls with WinFsp and should
improve performance on Windows.
---
 include/dwarfs/filesystem_v2.h |  3 +++
 include/dwarfs/metadata_v2.h   |  4 ++++
 src/dwarfs/filesystem_v2.cpp   |  1 +
 src/dwarfs/metadata_v2.cpp     |  2 ++
 src/dwarfs_main.cpp            | 22 ++++++++++++++--------
 5 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/include/dwarfs/filesystem_v2.h b/include/dwarfs/filesystem_v2.h
index fa8a854c..12b18cd9 100644
--- a/include/dwarfs/filesystem_v2.h
+++ b/include/dwarfs/filesystem_v2.h
@@ -169,6 +169,8 @@ class filesystem_v2 {
 
   size_t num_blocks() const { return impl_->num_blocks(); }
 
+  bool has_symlinks() const { return impl_->has_symlinks(); }
+
   class impl {
    public:
     virtual ~impl() = default;
@@ -207,6 +209,7 @@ class filesystem_v2 {
     virtual void set_num_workers(size_t num) = 0;
     virtual void set_cache_tidy_config(cache_tidy_config const& cfg) = 0;
     virtual size_t num_blocks() const = 0;
+    virtual bool has_symlinks() const = 0;
   };
 
  private:
diff --git a/include/dwarfs/metadata_v2.h b/include/dwarfs/metadata_v2.h
index 3a64c222..b382638f 100644
--- a/include/dwarfs/metadata_v2.h
+++ b/include/dwarfs/metadata_v2.h
@@ -132,6 +132,8 @@ class metadata_v2 {
 
   size_t block_size() const { return impl_->block_size(); }
 
+  bool has_symlinks() const { return impl_->has_symlinks(); }
+
   static std::pair<std::vector<uint8_t>, std::vector<uint8_t>>
   freeze(const thrift::metadata::metadata& data);
 
@@ -184,6 +186,8 @@ class metadata_v2 {
     virtual std::optional<chunk_range> get_chunks(int inode) const = 0;
 
     virtual size_t block_size() const = 0;
+
+    virtual bool has_symlinks() const = 0;
   };
 
  private:
diff --git a/src/dwarfs/filesystem_v2.cpp b/src/dwarfs/filesystem_v2.cpp
index bf11a17a..e5bc88b0 100644
--- a/src/dwarfs/filesystem_v2.cpp
+++ b/src/dwarfs/filesystem_v2.cpp
@@ -356,6 +356,7 @@ class filesystem_ final : public filesystem_v2::impl {
     ir_.set_cache_tidy_config(cfg);
   }
   size_t num_blocks() const override { return ir_.num_blocks(); }
+  bool has_symlinks() const override { return meta_.has_symlinks(); }
 
  private:
   filesystem_info const& get_info() const;
diff --git a/src/dwarfs/metadata_v2.cpp b/src/dwarfs/metadata_v2.cpp
index 4f9e9bef..052eb594 100644
--- a/src/dwarfs/metadata_v2.cpp
+++ b/src/dwarfs/metadata_v2.cpp
@@ -428,6 +428,8 @@ class metadata_ final : public metadata_v2::impl {
 
   size_t block_size() const override { return meta_.block_size(); }
 
+  bool has_symlinks() const override { return !meta_.symlink_table().empty(); }
+
  private:
   template <typename K>
   using set_type = folly::F14ValueSet<K>;
diff --git a/src/dwarfs_main.cpp b/src/dwarfs_main.cpp
index 09ca412c..66d2ddd9 100644
--- a/src/dwarfs_main.cpp
+++ b/src/dwarfs_main.cpp
@@ -1014,12 +1014,15 @@ int option_hdl(void* data, char const* arg, int key,
 
 #if DWARFS_FUSE_LOWLEVEL
 template <typename LoggerPolicy>
-void init_fuse_ops(struct fuse_lowlevel_ops& ops) {
+void init_fuse_ops(struct fuse_lowlevel_ops& ops,
+                   dwarfs_userdata const& userdata) {
   ops.init = &op_init<LoggerPolicy>;
   ops.lookup = &op_lookup<LoggerPolicy>;
   ops.getattr = &op_getattr<LoggerPolicy>;
   ops.access = &op_access<LoggerPolicy>;
-  ops.readlink = &op_readlink<LoggerPolicy>;
+  if (userdata.fs.has_symlinks()) {
+    ops.readlink = &op_readlink<LoggerPolicy>;
+  }
   ops.open = &op_open<LoggerPolicy>;
   ops.read = &op_read<LoggerPolicy>;
   ops.readdir = &op_readdir<LoggerPolicy>;
@@ -1029,11 +1032,14 @@ void init_fuse_ops(struct fuse_lowlevel_ops& ops) {
 }
 #else
 template <typename LoggerPolicy>
-void init_fuse_ops(struct fuse_operations& ops) {
+void init_fuse_ops(struct fuse_operations& ops,
+                   dwarfs_userdata const& userdata) {
   ops.init = &op_init<LoggerPolicy>;
   ops.getattr = &op_getattr<LoggerPolicy>;
   ops.access = &op_access<LoggerPolicy>;
-  ops.readlink = &op_readlink<LoggerPolicy>;
+  if (userdata.fs.has_symlinks()) {
+    ops.readlink = &op_readlink<LoggerPolicy>;
+  }
   ops.open = &op_open<LoggerPolicy>;
   ops.read = &op_read<LoggerPolicy>;
   ops.readdir = &op_readdir<LoggerPolicy>;
@@ -1060,9 +1066,9 @@ int run_fuse(struct fuse_args& args,
   ::memset(&fsops, 0, sizeof(fsops));
 
   if (userdata.opts.debuglevel >= logger::DEBUG) {
-    init_fuse_ops<debug_logger_policy>(fsops);
+    init_fuse_ops<debug_logger_policy>(fsops, userdata);
   } else {
-    init_fuse_ops<prod_logger_policy>(fsops);
+    init_fuse_ops<prod_logger_policy>(fsops, userdata);
   }
 
   int err = 1;
@@ -1108,9 +1114,9 @@ int run_fuse(struct fuse_args& args, char* mountpoint, int mt, int fg,
   ::memset(&fsops, 0, sizeof(fsops));
 
   if (userdata.opts.debuglevel >= logger::DEBUG) {
-    init_fuse_ops<debug_logger_policy>(fsops);
+    init_fuse_ops<debug_logger_policy>(fsops, userdata);
   } else {
-    init_fuse_ops<prod_logger_policy>(fsops);
+    init_fuse_ops<prod_logger_policy>(fsops, userdata);
   }
 
   int err = 1;