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 <[email protected]>

include/seastar/core/file-types.hh

@@ -22,6 +22,7 @@
 #pragma once
 
 #ifndef SEASTAR_MODULE
+#include <cstdint>
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <type_traits>
@@ -158,6 +159,18 @@ inline constexpr file_permissions operator&(file_permissions a, file_permissions
     return file_permissions(std::underlying_type_t<file_permissions>(a) & std::underlying_type_t<file_permissions>(b));
 }
 
+/// seastar::space_info is equivalent to std::filesystem::space_info
+/// with renamed members, to prevent a conflict with future::available()
+struct space_info {
+    std::uintmax_t capacity;
+    std::uintmax_t free_space;
+    std::uintmax_t available_space;
+
+    bool operator==(const space_info& o) const noexcept {
+        return capacity == o.capacity && free_space == o.free_space && available_space == o.available_space;
+    }
+};
+
 /// @}
 
 SEASTAR_MODULE_EXPORT_END

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<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 stat where a file is located.
+///
+/// \param name name of the file to inspect
+future<space_info> file_system_space(std::string_view name) noexcept;
+
 namespace experimental {
 /// \defgroup interprocess-module Interprocess Communication
 ///

src/core/reactor.cc

@@ -2263,6 +2263,26 @@ reactor::fstatfs(int fd) noexcept {
     });
 }
 
+future<space_info>
+reactor::file_system_space(std::string_view pathname) noexcept {
+    // Allocating memory for a filesystem::path can throw, hence the futurize_invoke
+    return futurize_invoke([this, pathname] {
+        return _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);
+        }).then([pathname = sstring(pathname)] (syscall_result_extra<std::filesystem::space_info> sr) {
+            sr.throw_fs_exception_if_error("file_system_space failed", pathname);
+            auto& fs_si = sr.extra;
+            return space_info{
+                .capacity = fs_si.capacity,
+                .free_space = fs_si.free,
+                .available_space = fs_si.available
+            };
+        });
+    });
+}
+
 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<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 +950,20 @@ 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();
+        struct statvfs st;
+        space_info si, si1;
+        do {
+            si = file_system_space(name).get();
+            st = engine().statvfs(name).get();
+            si1 = file_system_space(name).get();
+        } while (si1 != si);
+
+        BOOST_REQUIRE_EQUAL(st.f_blocks * st.f_frsize, si.capacity);
+        BOOST_REQUIRE_EQUAL(st.f_bfree * st.f_frsize, si.free_space);
+        BOOST_REQUIRE_EQUAL(st.f_bavail * st.f_frsize, si.available_space);
+    });
+}