file: add file_system_space

Return space_info for the filesystem identified
by the given file name.

space_info provides simpler and standard space information
about the filesystem, in contrast to the posix statvfs
which requires knowledge about the how to convert
f_block to bytes by multiplying by f_frsize.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>

include/seastar/core/reactor.hh

@@ -487,6 +487,7 @@ public:
         return file_accessible(pathname, access_flags::exists);
     }
     future<fs_type> file_system_at(std::string_view pathname) noexcept;
+    future<std::filesystem::space_info> file_system_space(std::string_view pathname) noexcept;
     future<struct statvfs> statvfs(std::string_view pathname) noexcept;
     future<> remove_file(std::string_view pathname) noexcept;
     future<> rename_file(std::string_view old_pathname, std::string_view new_pathname) noexcept;

include/seastar/core/seastar.hh

@@ -445,6 +445,11 @@ future<uint64_t> fs_avail(std::string_view name) noexcept;
 future<uint64_t> fs_free(std::string_view name) noexcept;
 /// @}
 
+/// Return filesystem-wide space_info where a file is located.
+///
+/// \param name name of the file in the filesystem to inspect
+future<std::filesystem::space_info> file_system_space(std::string_view name) noexcept;
+
 namespace experimental {
 /// \defgroup interprocess-module Interprocess Communication
 ///

src/core/reactor.cc

@@ -2263,6 +2263,17 @@ reactor::fstatfs(int fd) noexcept {
     });
 }
 
+future<std::filesystem::space_info>
+reactor::file_system_space(std::string_view pathname) noexcept {
+    auto sr = co_await _thread_pool->submit<syscall_result_extra<std::filesystem::space_info>>([path = std::filesystem::path(pathname)] {
+        std::error_code ec;
+        auto si = std::filesystem::space(path, ec);
+        return wrap_syscall(ec.value(), si);
+    });
+    sr.throw_fs_exception_if_error("std::filesystem::space failed", sstring(pathname));
+    co_return sr.extra;
+}
+
 future<struct statvfs>
 reactor::statvfs(std::string_view pathname) noexcept {
     // Allocating memory for a sstring can throw, hence the futurize_invoke

src/util/file.cc

@@ -128,6 +128,10 @@ future<uint64_t> fs_free(std::string_view name) noexcept {
     });
 }
 
+future<std::filesystem::space_info> file_system_space(std::string_view name) noexcept {
+    return engine().file_system_space(name);
+}
+
 future<stat_data> file_stat(std::string_view name, follow_symlink follow) noexcept {
     return engine().file_stat(name, follow);
 }

tests/unit/file_io_test.cc

@@ -19,11 +19,14 @@
  * Copyright (C) 2014-2015 Cloudius Systems, Ltd.
  */
 
+#include <filesystem>
+
 #include <seastar/testing/random.hh>
 #include <seastar/testing/test_case.hh>
 #include <seastar/testing/thread_test_case.hh>
 #include <seastar/testing/test_runner.hh>
 
+#include <seastar/core/reactor.hh>
 #include <seastar/core/seastar.hh>
 #include <seastar/core/semaphore.hh>
 #include <seastar/core/condition-variable.hh>
@@ -947,3 +950,16 @@ SEASTAR_TEST_CASE(test_oversized_io_works) {
         BOOST_REQUIRE((size_t)std::count_if(buf.get(), buf.get() + buf_size, [](auto x) { return x == 'a'; }) == buf_size);
     });
 }
+
+SEASTAR_TEST_CASE(test_file_system_space) {
+    return tmp_dir::do_with_thread([] (tmp_dir& t) {
+        const auto& name = t.get_path().native();
+        auto st = engine().statvfs(name).get();
+        auto si = file_system_space(name).get();
+
+        BOOST_REQUIRE_EQUAL(st.f_blocks * st.f_frsize, si.capacity);
+        BOOST_REQUIRE_LT(si.free, si.capacity);
+        BOOST_REQUIRE_LT(si.available, si.capacity);
+        BOOST_REQUIRE_LE(si.available, si.free);
+    });
+}