sapling/eden/fs/service/EdenStateDir.cpp

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This software may be used and distributed according to the terms of the
 * GNU General Public License version 2.
 */

#include "eden/fs/service/EdenStateDir.h"

#include <folly/Exception.h>
#include <folly/FileUtil.h>
#include <folly/logging/xlog.h>

using folly::StringPiece;

namespace facebook::eden {

namespace {
constexpr StringPiece kLockFileName{"lock"};
constexpr StringPiece kPidFileName{"pid"};
constexpr StringPiece kTakeoverSocketName{"takeover"};
constexpr StringPiece kThriftSocketName{"socket"};
constexpr PathComponentPiece kMountdSocketName{"mountd.socket"_pc};
} // namespace

EdenStateDir::EdenStateDir(AbsolutePathPiece path)
    : path_(path), lockPath_(path + PathComponentPiece(kLockFileName)) {}

EdenStateDir::~EdenStateDir() = default;

bool EdenStateDir::acquireLock() {
  auto lockFile =
      folly::File(lockPath_.value(), O_WRONLY | O_CREAT | O_CLOEXEC);
  try {
    if (!lockFile.try_lock()) {
      return false;
    }
  } catch (const std::system_error& ex) {
    throw std::runtime_error(fmt::format(
        "Error acquiring lock: {}. Another EdenFS process may have raced with "
        "this one. Try `eden start --wait` to check if EdenFS is starting and "
        "watch it's progress.",
        ex.what()));
  }

  takeoverLock(std::move(lockFile));
  return true;
}

void EdenStateDir::takeoverLock(folly::File lockFile) {
  writePidToLockFile(lockFile);
  int rc = fstat(lockFile.fd(), &lockFileStat_);
  folly::checkUnixError(rc, "error getting lock file attributes");
  lockFile_ = std::move(lockFile);

  // On Windows, also write the pid to a separate file.
  // Other processes cannot read the lock file while we are holding the lock,
  // so we store it in a separate file too.
  auto pidFilePath = path_ + PathComponentPiece(kPidFileName);
  folly::File pidFile(pidFilePath.c_str(), O_WRONLY | O_CREAT, 0644);
  writePidToLockFile(pidFile);
}

folly::File EdenStateDir::extractLock() {
  return std::move(lockFile_);
}

void EdenStateDir::writePidToLockFile(folly::File& lockFile) {
  // Write the PID (with a newline) to the lockfile.
  folly::ftruncateNoInt(lockFile.fd(), /* len */ 0);
  const auto pidContents = folly::to<std::string>(getpid(), "\n");
  folly::pwriteNoInt(lockFile.fd(), pidContents.data(), pidContents.size(), 0);
}

bool EdenStateDir::isLocked() const {
  // We only set lockFile_ once we have locked it,
  // so as long as this is set we have the lock.
  return bool(lockFile_);
}

bool EdenStateDir::isLockValid() const {
  if (!lockFile_) {
    return false;
  }

  // The st_dev and st_ino fields aren't valid on Windows, so skip the check
  // to see if the lock file is still valid.  Assume that if we acquired it
  // initially it is still valid.
  //
  // Windows generally makes it harder for users to delete or rename the
  // directory out from under an existing process while we have file handles
  // open, so this check isn't really as necessary.
#ifndef _WIN32
  struct stat st;
  int rc = stat(lockPath_.c_str(), &st);
  if (rc != 0) {
    int errnum = errno;
    XLOG(ERR) << "EdenFS lock file no longer appears valid: "
                 "failed to stat lock file: "
              << folly::errnoStr(errnum);
    return false;
  }

  bool isSameFile =
      (st.st_dev == lockFileStat_.st_dev && st.st_ino == lockFileStat_.st_ino);
  if (!isSameFile) {
    XLOG(ERR) << "EdenFS lock file no longer appears valid: "
                 "file has been replaced";
    return false;
  }
#endif

  return true;
}

AbsolutePath EdenStateDir::getThriftSocketPath() const {
  return path_ + PathComponentPiece{kThriftSocketName};
}

AbsolutePath EdenStateDir::getTakeoverSocketPath() const {
  return path_ + PathComponentPiece{kTakeoverSocketName};
}

AbsolutePath EdenStateDir::getMountdSocketPath() const {
  return path_ + kMountdSocketName;
}

AbsolutePath EdenStateDir::getCheckoutStateDir(StringPiece checkoutID) const {
  return path_ + PathComponent("clients") + PathComponent(checkoutID);
}

} // namespace facebook::eden