Add APIs to get group details and to change ownership of file.

There are a few calls in scylladb that bypass Seastar APIs when making libc
and syscall (getgrnam, chown), see issue scylladb/scylladb#17443.

This commit implements those APIs, which can be used to address the
issue scylladb/scylladb#17443

include/seastar/core/file.hh

@@ -61,6 +61,14 @@ struct directory_entry {
     std::optional<directory_entry_type> type;
 };
 
+/// Group details from the system group database
+struct group_details {
+    sstring group_name;
+    sstring group_passwd;
+    __gid_t group_id;
+    std::vector<sstring> group_members;
+};
+
 /// Filesystem object stat information
 struct stat_data {
     uint64_t  device_id;      // ID of device containing file

include/seastar/core/reactor.hh

@@ -493,6 +493,8 @@ public:
     future<> touch_directory(std::string_view name, file_permissions permissions = file_permissions::default_dir_permissions) noexcept;
     future<std::optional<directory_entry_type>>  file_type(std::string_view name, follow_symlink = follow_symlink::yes) noexcept;
     future<stat_data> file_stat(std::string_view pathname, follow_symlink) noexcept;
+    future<> chown(std::string_view filepath, uid_t owner, gid_t group);
+    future<std::optional<struct group_details>> getgrnam(std::string_view name);
     future<uint64_t> file_size(std::string_view pathname) noexcept;
     future<bool> file_accessible(std::string_view pathname, access_flags flags) noexcept;
     future<bool> file_exists(std::string_view pathname) noexcept {

include/seastar/core/seastar.hh

@@ -359,6 +359,21 @@ using follow_symlink = bool_class<follow_symlink_tag>;
 /// with follow_symlink::yes, or for the link itself, with follow_symlink::no.
 future<stat_data> file_stat(std::string_view name, follow_symlink fs = follow_symlink::yes) noexcept;
 
+/// Wrapper around getgrnam_r.
+/// If the provided group name does not exist in the group database, this call will return an empty optional.
+/// If the provided group name exists in the group database, the optional returned will contain the struct group_details information. 
+/// When an unexpected error is thrown by the getgrnam_r libc call, this function throws std::system_error with std::error_code.
+/// \param groupname name of the group
+///
+/// \return optional struct group_details of the group identified by name. struct group_details has details of the group from the group database.
+future<std::optional<struct group_details>> getgrnam(std::string_view name);
+
+/// Change the owner and group of file. This is a wrapper around chown syscall.
+/// The function throws std::system_error, when the chown syscall fails.
+/// \param filepath
+/// \param owner
+/// \param group
+future<> chown(std::string_view filepath, uid_t owner, gid_t group);
 /// Return the size of a file.
 ///
 /// \param name name of the file to return the size

src/core/reactor.cc

@@ -27,12 +27,14 @@ module;
 #include <cassert>
 #include <chrono>
 #include <cmath>
+#include <coroutine> 
 #include <exception>
 #include <filesystem>
 #include <fstream>
 #include <regex>
 #include <thread>
 
+#include <grp.h>
 #include <spawn.h>
 #include <sys/syscall.h>
 #include <sys/vfs.h>
@@ -2200,6 +2202,47 @@ void reactor::kill(pid_t pid, int sig) {
     ret.throw_if_error();
 }
 
+future<std::optional<struct group_details>> reactor::getgrnam(std::string_view name) {
+    syscall_result_extra<std::optional<struct group_details>> sr = co_await _thread_pool->submit<syscall_result_extra<std::optional<struct group_details>>>(
+        [name = sstring(name)] {
+            struct group grp;
+            struct group *result;
+            memset(&grp, 0, sizeof(struct group));
+            char buf[1024];
+            errno = 0;
+            int ret = ::getgrnam_r(name.c_str(), &grp, buf, sizeof(buf), &result);
+            if (!result) {
+                return wrap_syscall(ret, std::optional<struct group_details>(std::nullopt));
+            }
+
+            group_details gd;
+            gd.group_name = sstring(grp.gr_name);
+            gd.group_passwd = sstring(grp.gr_passwd);
+            gd.group_id = grp.gr_gid;
+            for (char **members = grp.gr_mem; *members != nullptr; ++members) {
+                gd.group_members.emplace_back(sstring(*members));
+            }
+            return wrap_syscall(ret, std::optional<struct group_details>(gd));
+        });
+
+    if (sr.result != 0) {
+        throw std::system_error(sr.ec());
+    }
+
+    co_return sr.extra;
+}
+
+future<> reactor::chown(std::string_view filepath, uid_t owner, gid_t group) {
+    syscall_result<int> sr = co_await _thread_pool->submit<syscall_result<int>>(
+        [filepath = sstring(filepath), owner, group] {
+            int ret = ::chown(filepath.c_str(), owner, group);
+            return wrap_syscall(ret);
+        });
+
+    sr.throw_if_error();
+    co_return;
+}
+
 future<stat_data>
 reactor::file_stat(std::string_view pathname, follow_symlink follow) noexcept {
     // Allocating memory for a sstring can throw, hence the futurize_invoke

src/core/syscall_result.hh

@@ -55,7 +55,7 @@ struct syscall_result {
             throw_fs_exception(reason, fs::path(path1), fs::path(path2));
         }
     }
-protected:
+
     std::error_code ec() const {
         return std::error_code(error, std::system_category());
     }

src/util/file.cc

@@ -132,6 +132,14 @@ future<stat_data> file_stat(std::string_view name, follow_symlink follow) noexce
     return engine().file_stat(name, follow);
 }
 
+future<std::optional<struct group_details>> getgrnam(std::string_view name) {
+    return engine().getgrnam(name);
+}
+
+future<> chown(std::string_view filepath, uid_t owner, gid_t group) {
+    return engine().chown(filepath, owner, group);
+}
+
 future<uint64_t> file_size(std::string_view name) noexcept {
     return engine().file_size(name);
 }

tests/unit/CMakeLists.txt

@@ -354,6 +354,9 @@ seastar_add_test (network_interface
 seastar_add_test (json_formatter
   SOURCES json_formatter_test.cc)
 
+seastar_add_test (libc_wrapper
+  SOURCES libc_wrapper_test.cc)
+
 seastar_add_test (locking
   SOURCES locking_test.cc)
 

tests/unit/libc_wrapper_test.cc

@@ -0,0 +1,44 @@
+/*
+ * This file is open source software, licensed to you under the terms
+ * of the Apache License, Version 2.0 (the "License").  See the NOTICE file
+ * distributed with this work for additional information regarding copyright
+ * ownership.  You may not use this file except in compliance with the License.
+ *
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/*
+ * Copyright (C) 2024 ScyllaDB.
+ */
+#include <coroutine>
+#include <iostream>
+
+#include <seastar/core/coroutine.hh>
+#include <seastar/core/reactor.hh>
+#include <seastar/core/seastar.hh>
+
+#include <seastar/testing/test_case.hh>
+
+using namespace seastar;
+
+SEASTAR_TEST_CASE(getgrnam_group_name_does_not_exist_test) {
+    // A better approach would be to use a test setup and teardown to create a fake group
+    // with members in it and in the teardown delete the fake group.
+    std::optional<struct group_details> grp = co_await getgrnam("roo");
+    BOOST_REQUIRE(!grp.has_value());
+}
+
+SEASTAR_TEST_CASE(getgrnam_group_name_exists_test) {
+    std::optional<struct group_details> grp = co_await getgrnam("root");
+    BOOST_REQUIRE(grp.has_value());
+    BOOST_REQUIRE_EQUAL(grp.value().group_name.c_str(), "root");
+}