mergerfs/src/fuse_readdir_cor.cpp

/*
  ISC License

  Copyright (c) 2026, Antonio SJ Musumeci <trapexit@spawn.link>

  Permission to use, copy, modify, and/or distribute this software for any
  purpose with or without fee is hereby granted, provided that the above
  copyright notice and this permission notice appear in all copies.

  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/

#include "fuse_readdir_cor.hpp"

#include "supported_getdents64.hpp"

#include "config.hpp"
#include "dirinfo.hpp"
#include "error.hpp"


FUSE::ReadDirCOR::ReadDirCOR(unsigned concurrency_,
                             unsigned max_queue_depth_)
  : _tp(concurrency_,max_queue_depth_,"readdir.cor")
{

}

FUSE::ReadDirCOR::~ReadDirCOR()
{

}

#ifdef MERGERFS_SUPPORTED_GETDENTS64
#include "fuse_readdir_cor_getdents.icpp"
#else
#include "fuse_readdir_cor_readdir.icpp"
#endif

// Uses a per-call mutex. Lifetime is one readdir operation. It
// serializes the dirent-merge step (dedup'ing of names + append to
// dirents list) across at-most-branches-worth of parallel worker
// tasks. Per-branch opendir + getdents64 run fully outside the
// critical section, so the lock holds only long enough to merge each
// batch.
static
inline
int
_concurrent_readdir(ThreadPool          &tp_,
                     const Branches::Ptr  branches_,
                    const fs::path      &rel_dirpath_,
                    fuse_dirents_t      *dirents_)
{
  HashSet names;
  Mutex mutex;
  std::vector<std::future<int>> futures;

  fuse_dirents_reset(dirents_);
  futures.reserve(branches_->size());

  for(const auto &branch : *branches_)
    {
      auto func =
        [&,dirents_]()
        {
          return ::_readdir(branch.path,
                            rel_dirpath_,
                            names,
                            dirents_,
                            mutex);
        };

      auto rv = tp_.enqueue_task(std::move(func));

      futures.emplace_back(std::move(rv));
    }

  Err err;
  for(auto &future : futures)
    err = future.get();

  return err;
}

int
FUSE::ReadDirCOR::operator()(const fuse_req_ctx_t   *ctx_,
                             const fuse_file_info_t *ffi_,
                             fuse_dirents_t         *dirents_)
{
  DirInfo *di = DirInfo::from_fh(ffi_->fh);

  if(not di)
    return -EBADF;

  return ::_concurrent_readdir(_tp,
                               cfg.branches,
                               di->fusepath,
                               dirents_);
}