Merge 'Simplify fs-info getting in make_file_impl()' from Pavel Emely…

…anov

The helper looks up in the map of fs-info-s twice and returns the chain of ready futures on the common paths. This PR makes things simpler.

Closes scylladb#2297

* github.com:scylladb/seastar:
  file: Use lighter access to map of fs-info-s
  file: Fix indentation after previous patch
  file: Don't return chain of ready futures from make_file_impl

src/core/file.cc

@@ -1078,8 +1078,9 @@ make_file_impl(int fd, file_open_options options, int flags, struct stat st) noe
  auto st_dev = st.st_dev;
  static thread_local std::unordered_map<decltype(st_dev), internal::fs_info> s_fstype;
 
- future<> get_fs_info = s_fstype.count(st_dev) ? make_ready_future<>() :
- engine().fstatfs(fd).then([fd, st_dev] (struct statfs sfs) {
+ auto i = s_fstype.find(st_dev);
+ if (i == s_fstype.end()) [[unlikely]] {
+ return engine().fstatfs(fd).then([fd, options = std::move(options), flags, st = std::move(st)] (struct statfs sfs) {
  internal::fs_info fsi;
  fsi.block_size = sfs.f_bsize;
  switch (sfs.f_type) {
@@ -1126,15 +1127,16 @@ make_file_impl(int fd, file_open_options options, int flags, struct stat st) noe
  fsi.fsync_is_exclusive = true;
  fsi.nowait_works = false;
  }
- s_fstype[st_dev] = std::move(fsi);
+ s_fstype.insert(std::make_pair(st.st_dev, std::move(fsi)));
+ return make_file_impl(fd, std::move(options), flags, std::move(st));
  });
- return get_fs_info.then([st_dev, fd, flags, options = std::move(options)] () mutable {
- const internal::fs_info& fsi = s_fstype[st_dev];
-  if (!fsi.append_challenged || options.append_is_unlikely || ((flags & O_ACCMODE) == O_RDONLY)) {
-  return make_ready_future<shared_ptr<file_impl>>(make_shared<posix_file_real_impl>(fd, open_flags(flags), std::move(options), fsi, st_dev));
- }
-  return make_ready_future<shared_ptr<file_impl>>(make_shared<append_challenged_posix_file_impl>(fd, open_flags(flags), std::move(options), fsi, st_dev));
- });
+ }
+
+ const internal::fs_info& fsi = i->second;
+ if (!fsi.append_challenged || options.append_is_unlikely || ((flags & O_ACCMODE) == O_RDONLY)) {
+ return make_ready_future<shared_ptr<file_impl>>(make_shared<posix_file_real_impl>(fd, open_flags(flags), std::move(options), fsi, st_dev));
+ }
+ return make_ready_future<shared_ptr<file_impl>>(make_shared<append_challenged_posix_file_impl>(fd, open_flags(flags), std::move(options), fsi, st_dev));
 }
 
 file::file(seastar::file_handle&& handle) noexcept