[libc] Implement fchown

libc/config/linux/aarch64/entrypoints.txt

@@ -327,6 +327,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.execve
     libc.src.unistd.faccessat
     libc.src.unistd.fchdir
+    libc.src.unistd.fchown
     libc.src.unistd.fpathconf
     libc.src.unistd.fsync
     libc.src.unistd.ftruncate

libc/config/linux/x86_64/entrypoints.txt

@@ -334,6 +334,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.execve
     libc.src.unistd.faccessat
     libc.src.unistd.fchdir
+    libc.src.unistd.fchown
     libc.src.unistd.fpathconf
     libc.src.unistd.fsync
     libc.src.unistd.ftruncate

libc/include/unistd.yaml

@@ -120,6 +120,14 @@ functions:
     return_type: int
     arguments:
       - type: int
+  - name: fchown
+    standards:
+      - POSIX
+    return_type: int
+    arguments:
+      - type: int
+      - type: uid_t
+      - type: gid_t
   - name: fork
     standards:
       - POSIX

libc/src/unistd/CMakeLists.txt

@@ -76,6 +76,13 @@ add_entrypoint_object(
     .${LIBC_TARGET_OS}.fchdir
 )
 
+add_entrypoint_object(
+  fchown
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.fchown
+)
+
 add_entrypoint_object(
   fork
   ALIAS

libc/src/unistd/fchown.h

@@ -0,0 +1,22 @@
+//===-- Implementation header for fchown ------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_UNISTD_FCHOWN_H_
+#define LLVM_LIBC_SRC_UNISTD_FCHOWN_H_
+
+#include "hdr/types/gid_t.h"
+#include "hdr/types/uid_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int fchown(int fildes, uid_t owner, gid_t group);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_UNISTD_FCHOWN_H_

libc/src/unistd/linux/CMakeLists.txt

@@ -120,6 +120,20 @@ add_entrypoint_object(
     libc.src.errno.errno
 )
 
+add_entrypoint_object(
+  fchown
+  SRCS
+    fchown.cpp
+  HDRS
+    ../fchown.h
+  DEPENDS
+    libc.hdr.types.uid_t
+    libc.hdr.types.gid_t
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
 add_entrypoint_object(
   fork
   SRCS

libc/src/unistd/linux/fchown.cpp

@@ -0,0 +1,29 @@
+//===-- Linux implementation of fchown ------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/fchown.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, fchown, (int fildes, uid_t owner, gid_t group)) {
+  int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_fchown, fildes, owner, group);
+  if (ret < 0) {
+    libc_errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/test/src/unistd/CMakeLists.txt

@@ -146,6 +146,26 @@ add_libc_unittest(
     libc.test.UnitTest.ErrnoSetterMatcher
 )
 
+add_libc_unittest(
+  fchown_test
+  SUITE
+    libc_unistd_unittests
+  SRCS
+    fchown_test.cpp
+  DEPENDS
+    libc.hdr.fcntl_macros
+    libc.include.unistd
+    libc.src.errno.errno
+    libc.src.unistd.fchown
+    libc.src.unistd.close
+    libc.src.unistd.unlink
+    libc.src.fcntl.open
+    libc.src.unistd.getuid
+    libc.src.unistd.getgid
+    libc.test.UnitTest.ErrnoCheckingTest
+    libc.test.UnitTest.ErrnoSetterMatcher
+)
+
 add_libc_unittest(
   ftruncate_test
   SUITE

libc/test/src/unistd/fchown_test.cpp

@@ -0,0 +1,50 @@
+//===-- Unittests for fchown ----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/fcntl/open.h"
+#include "src/unistd/close.h"
+#include "src/unistd/fchown.h"
+#include "src/unistd/getgid.h"
+#include "src/unistd/getuid.h"
+#include "src/unistd/unlink.h"
+
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+#include "test/UnitTest/Test.h"
+
+#include "hdr/fcntl_macros.h"
+#include <sys/stat.h>
+
+using LlvmLibcFchownTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST_F(LlvmLibcFchownTest, FchownSuccess) {
+  using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Succeeds;
+  uid_t my_uid = LIBC_NAMESPACE::getuid();
+  gid_t my_gid = LIBC_NAMESPACE::getgid();
+  constexpr const char *FILENAME = "fchown.test";
+  auto TEST_FILE = libc_make_test_file_path(FILENAME);
+
+  // Create a test file.
+  int write_fd = LIBC_NAMESPACE::open(TEST_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_GT(write_fd, 0);
+
+  // Change the ownership of the file.
+  ASSERT_THAT(LIBC_NAMESPACE::fchown(write_fd, my_uid, my_gid), Succeeds(0));
+
+  // Close the file descriptor.
+  ASSERT_THAT(LIBC_NAMESPACE::close(write_fd), Succeeds(0));
+
+  // Clean up the test file.
+  ASSERT_THAT(LIBC_NAMESPACE::unlink(TEST_FILE), Succeeds(0));
+}
+
+TEST_F(LlvmLibcFchownTest, ChownInvalidFileDescriptor) {
+  using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Fails;
+  ASSERT_THAT(LIBC_NAMESPACE::fchown(-1, 1000, 1000), Fails(EBADF));
+}