file: add file_system_stat

Return an abstract file_system_stat_data representing
the system statvfs for the filesystem identified
by the given file name.

The motivation is implementing a disk-space monitor
in scylladb.

Signed-off-by: Benny Halevy <[email protected]>

include/seastar/core/file-types.hh

@@ -180,6 +180,22 @@ struct stat_data {
     std::chrono::system_clock::time_point time_changed;   // Time of last status change (either content or attributes)
 };
 
+/// Filesystem-wide stat information
+/// See statvfs(3)
+struct file_system_stat_data {
+    size_t block_size;          // Filesystem block size
+    size_t fragment_size;       // Fragment size
+    uint64_t size_in_bytes;     // Size of filesystem in bytes
+    uint64_t free_bytes;        // Free space in bytes
+    uint64_t available_bytes;   // Available space in bytes for unprivileged users
+    uint64_t files_total;       // Number of inodes
+    uint64_t files_free;        // Number of free inodes
+    uint64_t files_available;   // Number of free inodes for unprivileged users
+    uint64_t fsid;              // Filesystem ID
+    uint64_t mount_flags;       // Mount flags
+    size_t max_filename_length; // Maximum filename length
+};
+
 /// @}
 
 SEASTAR_MODULE_EXPORT_END

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<file_system_stat_data> file_system_stat(std::string_view name) noexcept;
+
 namespace experimental {
 /// \defgroup interprocess-module Interprocess Communication
 ///

src/util/file.cc

@@ -24,6 +24,7 @@
 module;
 #endif
 
+#include <coroutine>
 #include <cstdint>
 #include <deque>
 #include <filesystem>
@@ -128,6 +129,23 @@ future<uint64_t> fs_free(std::string_view name) noexcept {
     });
 }
 
+future<file_system_stat_data> file_system_stat(std::string_view name) noexcept {
+    struct statvfs st = co_await engine().statvfs(name);
+    co_return file_system_stat_data{
+        .block_size = st.f_bsize,
+        .fragment_size = st.f_frsize,
+        .size_in_bytes = (uint64_t)st.f_blocks * st.f_frsize,
+        .free_bytes = (uint64_t)st.f_bfree * st.f_frsize,
+        .available_bytes = (uint64_t)st.f_bavail * st.f_frsize,
+        .files_total = st.f_files,
+        .files_free = st.f_ffree,
+        .files_available = st.f_favail,
+        .fsid = st.f_fsid,
+        .mount_flags = st.f_flag,
+        .max_filename_length = st.f_namemax,
+    };
+}
+
 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

@@ -947,3 +947,13 @@ 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_stat) {
+    return tmp_dir::do_with_thread([] (tmp_dir& t) {
+        const auto& name = t.get_path().native();
+        auto fs_stat = file_system_stat(name).get();
+
+        BOOST_REQUIRE_GE(fs_stat.size_in_bytes, fs_stat.free_bytes);
+        BOOST_REQUIRE_GE(fs_stat.free_bytes, fs_stat.available_bytes);
+    });
+}