Revise the logic of readdir to make sure each dirent has a unique cookie, and recycle expired readdir contexts

Author: excelle08

src/directory.cpp

@@ -146,18 +146,16 @@ int Directory::ReadAndReply(fuse_req_t req, size_t size, off_t off) {
     return fuse_reply_err(req, EISDIR);
 }
 
+/* The cookie uses 32 bits, with the higher 16 bit the key to the readdir
+ * context, and the lower 16 bit representing the index of the directory entry.
+ */
 Directory::ReadDirCtx* Directory::PrepareReaddir(off_t cookie) {
+    off_t key = 0;
     if (cookie != 0) {
         /* NOTE: Will throw std::out_of_range if no entry is found */
-        Directory::ReadDirCtx* ctx = readdirStates.at(cookie);
-
-        /* If we have reached the end of the iterator, we should destroy this context 
-         * to release memory */
-        if (ctx->it == ctx->children.end()) {
-            Directory::readdirStates.erase(cookie);
-            delete ctx;
-            throw(std::out_of_range("Not found"));
-        }
+        key = (cookie & 0xffff0000) >> 16;
+        Directory::ReadDirCtx* ctx = readdirStates.at(key);
+
         return ctx;
     }
     /* Make a copy of children */
@@ -166,16 +164,31 @@ Directory::ReadDirCtx* Directory::PrepareReaddir(off_t cookie) {
     lk.unlock();
 
     /* Add it to the table */
-    cookie = rand();
+    key = rand() & 0xffff;
     /* Make sure there is no duplicate */
-    while (readdirStates.find(cookie) != readdirStates.end()) {
-        cookie = rand();
+    while (readdirStates.find(key) != readdirStates.end()) {
+      key = rand() & 0xffff;
     }
+    cookie = 0;
+    cookie = key << 16;
     ReadDirCtx *newctx = new ReadDirCtx(cookie, copiedChildren);
-    readdirStates.insert({cookie, newctx});
+    readdirStates.insert({key, newctx});
     return newctx;
 }
 
+void Directory::RecycleStates() {
+  // find context objects whose iterators have reached the end, and free them
+  for (auto ctxiter = readdirStates.begin(); ctxiter != readdirStates.end();) {
+    Directory::ReadDirCtx *ctx = ctxiter->second;
+    if (ctx->it == ctx->children.end()) {
+      delete ctx;
+      ctxiter = readdirStates.erase(ctxiter);
+    } else {
+      ++ctxiter;
+    }
+  }
+}
+
 bool Directory::IsEmpty() {
     std::shared_lock<std::shared_mutex> lk(childrenRwSem);
     for (auto it = m_children.begin(); it != m_children.end(); ++it) {

src/directory.hpp

@@ -28,6 +28,7 @@ class Directory : public Inode {
 
     static std::unordered_map<off_t, Directory::ReadDirCtx *> readdirStates;
     ReadDirCtx* PrepareReaddir(off_t cookie);
+    void RecycleStates();
     friend class FuseRamFs;
 public:
     ~Directory() {}

src/fuse_cpp_ramfs.cpp

@@ -682,7 +682,7 @@ void FuseRamFs::FuseReadDir(fuse_req_t req, fuse_ino_t ino, size_t size,
                                         bufSize - bytesAdded,
                                         ctx->it->first.c_str(),
                                         &stbuf,
-                                        ctx->cookie);
+                                        ++ctx->cookie);
         if (bytesAdded > bufSize) {
             // Oops. There wasn't enough space for that last item. Back up and exit.
             --(ctx->it);
@@ -694,6 +694,7 @@ void FuseRamFs::FuseReadDir(fuse_req_t req, fuse_ino_t ino, size_t size,
         }
     }
 
+    dir->RecycleStates();
     fuse_reply_buf(req, buf, bytesAdded);
     std::free(buf);
 }