fusebox/fuse_request.h

// Copyright 2021 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef FUSEBOX_FUSE_REQUEST_H_
#define FUSEBOX_FUSE_REQUEST_H_

#include <fuse_lowlevel.h>

#include <memory>
#include <string>
#include <vector>

namespace fusebox {

/**
 * Kernel FUSE low level request responders: FuseRequest stores a Kernel
 * fuse_req_t type in member req_ and replies to that req_ with the FUSE
 * operation results (the response).
 *
 * Derived classes specialize the response for the given req_, and store
 * any request parameters needed to complete the operation.
 *
 * Note: the classes only define the low level FUSE request and response
 * API, they do not perform FUSE operations.
 */

class FuseRequest {
 protected:
  explicit FuseRequest(fuse_req_t req, fuse_file_info* fi = nullptr);
  FuseRequest(const FuseRequest&) = delete;
  FuseRequest& operator=(const FuseRequest&) = delete;
  virtual ~FuseRequest();

 public:
  int flags() const { return flags_; }
  uint64_t fh() const { return fh_; }
  bool IsInterrupted() const;
  int ReplyError(int error);

 protected:
  const fuse_req_t req_;
  bool replied_ = false;
  uint64_t fh_;
  int flags_;
};

// FUSE request with an OK response.
class OkRequest : public FuseRequest {
 public:
  explicit OkRequest(fuse_req_t req, fuse_file_info* fi = nullptr)
      : FuseRequest(req, fi) {}
  void ReplyOk();
};

// FUSE request with a none response.
class NoneRequest : public FuseRequest {
 public:
  explicit NoneRequest(fuse_req_t req) : FuseRequest(req) {}
  void ReplyNone();
};

// FUSE request with an attribute stat response.
class AttrRequest : public FuseRequest {
 public:
  AttrRequest(fuse_req_t req, fuse_file_info* fi) : FuseRequest(req, fi) {}
  void ReplyAttr(const struct stat& attr, double timeout);
};

// FUSE request with a fuse_entry_param response.
class EntryRequest : public FuseRequest {
 public:
  explicit EntryRequest(fuse_req_t req) : FuseRequest(req) {}
  void ReplyEntry(const fuse_entry_param& entry);
};

// FUSE request with an open file handle response.
class OpenRequest : public FuseRequest {
 public:
  OpenRequest(fuse_req_t req, fuse_file_info* fi) : FuseRequest(req, fi) {}
  void ReplyOpen(uint64_t fh);
};

// FUSE request with an entry create response.
class CreateRequest : public FuseRequest {
 public:
  explicit CreateRequest(fuse_req_t req, fuse_file_info* fi)
      : FuseRequest(req, fi) {}
  void ReplyCreate(const fuse_entry_param& entry, uint64_t fh);
};

// FUSE request with a data buffer response.
class BufferRequest : public FuseRequest {
 public:
  BufferRequest(fuse_req_t req, fuse_file_info* fi) : FuseRequest(req, fi) {}
  void ReplyBuffer(const void* data, size_t size);
};

// FUSE request with a bytes written count response.
class WriteRequest : public FuseRequest {
 public:
  explicit WriteRequest(fuse_req_t req, fuse_file_info* fi)
      : FuseRequest(req, fi) {}
  void ReplyWrite(size_t count);
};

// FUSE request with a DirEntry list response.
class DirEntryRequest : public FuseRequest {
 public:
  DirEntryRequest(fuse_req_t req,
                  fuse_file_info* fi,
                  fuse_ino_t ino,
                  size_t size,
                  off_t off);

  // Directory ino.
  fuse_ino_t parent() const { return parent_; }

  // Entry buffer |buf_| size.
  size_t size() const { return size_; }

  // Add entry to |buf_|. Returns true if the entry was added.
  bool AddEntry(const struct DirEntry& entry, off_t offset);

  // Space used in |buf_| by the added entries.
  size_t used() const { return off_; }

  // Offset to the next entry.
  off_t offset() const { return offset_; }

  // Reply with the entry buffer result.
  void ReplyDone();

 private:
  fuse_ino_t parent_;
  const size_t size_;
  off_t offset_;
  std::unique_ptr<char[]> buf_;
  size_t off_ = 0;
};

class DirEntryResponse {
 public:
  DirEntryResponse(fuse_ino_t ino, uint64_t handle);

  // Directory ino.
  fuse_ino_t parent() const { return parent_; }

  // File handle.
  uint64_t handle() const { return handle_; }

  // Append |entry| DirEntry to the DirEntry list.
  void Append(std::vector<struct DirEntry> entry, bool end = false);

  // Append |request| to the DirEntryRequest list.
  void Append(std::unique_ptr<DirEntryRequest> request);

  // Append errno |error| to the DirEntry list. Returns |error|.
  int Append(int error);

 private:
  // Called on Append() to respond to DirEntry requests.
  void Respond();

 private:
  // Directory ino.
  fuse_ino_t const parent_;

  // The open file handle of the directory: opendir(2).
  uint64_t const handle_;

  // List of DirEntryRequest received from Kernel Fuse.
  std::vector<std::unique_ptr<DirEntryRequest>> request_;

  // List of DirEntry from the file system: readdir(2).
  std::vector<struct DirEntry> entry_;

  // Error state of the DirEntry list.
  int error_ = 0;

  // True when the DirEntry list is complete.
  bool end_ = false;
};

struct DirEntry {
  ino_t ino;
  std::string name;
  mode_t mode;
};

}  // namespace fusebox

#endif  // FUSEBOX_FUSE_REQUEST_H_