[libc-commits] [libc] [libc] Implement lchown in unistd (PR #230851)
via libc-commits
libc-commits at lists.llvm.org
Sat Oct 10 13:18:23 PDT 2026
llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libc
Author: Aman Maurya (amanmaurya92)
<details>
<summary>Changes</summary>
Implement the standard POSIX function `lchown(const char *path, uid_t owner, gid_t group)` in `<unistd.h>`.
Fixes #<!-- -->230837.
---
Full diff: https://github.com/llvm/llvm-project/pull/230851.diff
13 Files Affected:
- (modified) libc/config/linux/aarch64/entrypoints.txt (+1)
- (modified) libc/config/linux/arm/entrypoints.txt (+1)
- (modified) libc/config/linux/riscv/entrypoints.txt (+1)
- (modified) libc/config/linux/x86_64/entrypoints.txt (+1)
- (modified) libc/include/unistd.yaml (+8)
- (modified) libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt (+15)
- (added) libc/src/__support/OSUtil/linux/syscall_wrappers/lchown.h (+43)
- (modified) libc/src/unistd/CMakeLists.txt (+7)
- (added) libc/src/unistd/lchown.h (+22)
- (modified) libc/src/unistd/linux/CMakeLists.txt (+15)
- (added) libc/src/unistd/linux/lchown.cpp (+32)
- (modified) libc/test/src/unistd/CMakeLists.txt (+23)
- (added) libc/test/src/unistd/lchown_test.cpp (+88)
``````````diff
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index b8a9a5cff2040..a8f0b13f6ff77 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -484,6 +484,7 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.unistd.getgid
libc.src.unistd.getuid
libc.src.unistd.isatty
+ libc.src.unistd.lchown
libc.src.unistd.link
libc.src.unistd.linkat
libc.src.unistd.lseek
diff --git a/libc/config/linux/arm/entrypoints.txt b/libc/config/linux/arm/entrypoints.txt
index ac66f1f518484..e6d1a91e3cc10 100644
--- a/libc/config/linux/arm/entrypoints.txt
+++ b/libc/config/linux/arm/entrypoints.txt
@@ -280,6 +280,7 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.unistd.getgid
libc.src.unistd.getuid
libc.src.unistd.isatty
+ libc.src.unistd.lchown
libc.src.unistd.link
libc.src.unistd.linkat
libc.src.unistd.lseek
diff --git a/libc/config/linux/riscv/entrypoints.txt b/libc/config/linux/riscv/entrypoints.txt
index 0728bd41a40f9..053ed3ab6a644 100644
--- a/libc/config/linux/riscv/entrypoints.txt
+++ b/libc/config/linux/riscv/entrypoints.txt
@@ -504,6 +504,7 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.unistd.getgid
libc.src.unistd.getuid
libc.src.unistd.isatty
+ libc.src.unistd.lchown
libc.src.unistd.link
libc.src.unistd.linkat
libc.src.unistd.lseek
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 2df3fb0dfb363..c9426204ecb5e 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -524,6 +524,7 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.unistd.getgid
libc.src.unistd.getuid
libc.src.unistd.isatty
+ libc.src.unistd.lchown
libc.src.unistd.link
libc.src.unistd.linkat
libc.src.unistd.lseek
diff --git a/libc/include/unistd.yaml b/libc/include/unistd.yaml
index 92951152b7ca7..92350cf2e90ee 100644
--- a/libc/include/unistd.yaml
+++ b/libc/include/unistd.yaml
@@ -397,6 +397,14 @@ functions:
- type: int
guard: null
attributes: []
+ - name: lchown
+ standards:
+ - posix
+ return_type: int
+ arguments:
+ - type: const char *
+ - type: uid_t
+ - type: gid_t
- name: link
standards:
- posix
diff --git a/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt b/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt
index a3f56b1117c2b..38698ccc4feaf 100644
--- a/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt
+++ b/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt
@@ -789,6 +789,21 @@ add_header_library(
libc.src.__support.macros.config
)
+add_header_library(
+ lchown
+ HDRS
+ lchown.h
+ DEPENDS
+ libc.hdr.fcntl_macros
+ libc.hdr.types.gid_t
+ libc.hdr.types.uid_t
+ libc.include.sys_syscall
+ libc.src.__support.OSUtil.osutil
+ libc.src.__support.common
+ libc.src.__support.error_or
+ libc.src.__support.macros.config
+)
+
add_header_library(
ftruncate
HDRS
diff --git a/libc/src/__support/OSUtil/linux/syscall_wrappers/lchown.h b/libc/src/__support/OSUtil/linux/syscall_wrappers/lchown.h
new file mode 100644
index 0000000000000..4633012fb6216
--- /dev/null
+++ b/libc/src/__support/OSUtil/linux/syscall_wrappers/lchown.h
@@ -0,0 +1,43 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Syscall wrapper for lchown.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_SYSCALL_WRAPPERS_LCHOWN_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_SYSCALL_WRAPPERS_LCHOWN_H
+
+#include "hdr/fcntl_macros.h"
+#include "hdr/types/gid_t.h"
+#include "hdr/types/uid_t.h"
+#include "src/__support/OSUtil/linux/syscall.h" // syscall_checked
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include <sys/syscall.h> // For syscall numbers
+
+namespace LIBC_NAMESPACE_DECL {
+namespace linux_syscalls {
+
+LIBC_INLINE ErrorOr<int> lchown(const char *path, uid_t owner, gid_t group) {
+#ifdef SYS_fchownat
+ return syscall_checked<int>(SYS_fchownat, AT_FDCWD, path, owner, group,
+ AT_SYMLINK_NOFOLLOW);
+#elif defined(SYS_lchown)
+ return syscall_checked<int>(SYS_lchown, path, owner, group);
+#else
+#error "fchownat and lchown syscalls not available."
+#endif
+}
+
+} // namespace linux_syscalls
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_SYSCALL_WRAPPERS_LCHOWN_H
diff --git a/libc/src/unistd/CMakeLists.txt b/libc/src/unistd/CMakeLists.txt
index a9228513c0312..1944e86756717 100644
--- a/libc/src/unistd/CMakeLists.txt
+++ b/libc/src/unistd/CMakeLists.txt
@@ -280,6 +280,13 @@ add_entrypoint_object(
.${LIBC_TARGET_OS}.isatty
)
+add_entrypoint_object(
+ lchown
+ ALIAS
+ DEPENDS
+ .${LIBC_TARGET_OS}.lchown
+)
+
add_entrypoint_object(
link
ALIAS
diff --git a/libc/src/unistd/lchown.h b/libc/src/unistd/lchown.h
new file mode 100644
index 0000000000000..2d35bcdb0bab6
--- /dev/null
+++ b/libc/src/unistd/lchown.h
@@ -0,0 +1,22 @@
+//===-- Implementation header for lchown ------------------------*- 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_LCHOWN_H
+#define LLVM_LIBC_SRC_UNISTD_LCHOWN_H
+
+#include "hdr/types/gid_t.h"
+#include "hdr/types/uid_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int lchown(const char *path, uid_t owner, gid_t group);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_UNISTD_LCHOWN_H
diff --git a/libc/src/unistd/linux/CMakeLists.txt b/libc/src/unistd/linux/CMakeLists.txt
index 2555c9b700982..0b641dd5011f0 100644
--- a/libc/src/unistd/linux/CMakeLists.txt
+++ b/libc/src/unistd/linux/CMakeLists.txt
@@ -457,6 +457,21 @@ add_entrypoint_object(
libc.src.errno.errno
)
+add_entrypoint_object(
+ lchown
+ SRCS
+ lchown.cpp
+ HDRS
+ ../lchown.h
+ DEPENDS
+ libc.hdr.types.gid_t
+ libc.hdr.types.uid_t
+ libc.src.__support.OSUtil.linux.syscall_wrappers.lchown
+ libc.src.__support.common
+ libc.src.__support.libc_errno
+ libc.src.__support.macros.config
+)
+
add_entrypoint_object(
link
SRCS
diff --git a/libc/src/unistd/linux/lchown.cpp b/libc/src/unistd/linux/lchown.cpp
new file mode 100644
index 0000000000000..9b493e1a5e9a0
--- /dev/null
+++ b/libc/src/unistd/linux/lchown.cpp
@@ -0,0 +1,32 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Linux implementation of lchown.
+///
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/lchown.h"
+
+#include "src/__support/OSUtil/linux/syscall_wrappers/lchown.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, lchown, (const char *path, uid_t owner, gid_t group)) {
+ auto ret = linux_syscalls::lchown(path, owner, group);
+ if (!ret.has_value()) {
+ libc_errno = ret.error();
+ return -1;
+ }
+ return 0;
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/test/src/unistd/CMakeLists.txt b/libc/test/src/unistd/CMakeLists.txt
index 7588440c3d8df..60940efc0f05b 100644
--- a/libc/test/src/unistd/CMakeLists.txt
+++ b/libc/test/src/unistd/CMakeLists.txt
@@ -304,6 +304,29 @@ add_libc_test(
libc.test.UnitTest.ErrnoSetterMatcher
)
+add_libc_test(
+ lchown_test
+ SUITE
+ libc_unistd_unittests
+ SRCS
+ lchown_test.cpp
+ DEPENDS
+ libc.hdr.sys_stat_macros
+ libc.hdr.fcntl_macros
+ libc.include.unistd
+ libc.src.__support.CPP.scope
+ libc.src.errno.errno
+ libc.src.fcntl.open
+ libc.src.unistd.close
+ libc.src.unistd.getgid
+ libc.src.unistd.getuid
+ libc.src.unistd.lchown
+ libc.src.unistd.symlink
+ libc.src.unistd.unlink
+ libc.test.UnitTest.ErrnoCheckingTest
+ libc.test.UnitTest.ErrnoSetterMatcher
+)
+
add_libc_test(
link_test
SUITE
diff --git a/libc/test/src/unistd/lchown_test.cpp b/libc/test/src/unistd/lchown_test.cpp
new file mode 100644
index 0000000000000..226f29d5ea704
--- /dev/null
+++ b/libc/test/src/unistd/lchown_test.cpp
@@ -0,0 +1,88 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Unittests for lchown.
+///
+//===----------------------------------------------------------------------===//
+
+#include "hdr/fcntl_macros.h"
+#include "hdr/sys_stat_macros.h"
+#include "src/__support/CPP/scope.h"
+#include "src/fcntl/open.h"
+#include "src/unistd/close.h"
+#include "src/unistd/getgid.h"
+#include "src/unistd/getuid.h"
+#include "src/unistd/lchown.h"
+#include "src/unistd/symlink.h"
+#include "src/unistd/unlink.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+#include "test/UnitTest/Test.h"
+
+using namespace LIBC_NAMESPACE::testing::ErrnoSetterMatcher;
+using LlvmLibcLchownTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST_F(LlvmLibcLchownTest, LchownSuccessRegularFile) {
+ uid_t my_uid = LIBC_NAMESPACE::getuid();
+ gid_t my_gid = LIBC_NAMESPACE::getgid();
+ constexpr const char *FILENAME = "lchown_regular.test";
+ auto TEST_FILE = libc_make_test_file_path(FILENAME);
+
+ int write_fd = LIBC_NAMESPACE::open(TEST_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+ ASSERT_ERRNO_SUCCESS();
+ ASSERT_GT(write_fd, 0);
+ ASSERT_THAT(LIBC_NAMESPACE::close(write_fd), Succeeds(0));
+
+ LIBC_NAMESPACE::cpp::scope_exit cleanup(
+ [&] { EXPECT_THAT(LIBC_NAMESPACE::unlink(TEST_FILE), Succeeds(0)); });
+
+ // Change ownership to current user/group on a regular file.
+ ASSERT_THAT(LIBC_NAMESPACE::lchown(TEST_FILE, my_uid, my_gid), Succeeds(0));
+
+ // Passing -1 for owner and group leaves them unchanged without error.
+ ASSERT_THAT(LIBC_NAMESPACE::lchown(TEST_FILE, static_cast<uid_t>(-1),
+ static_cast<gid_t>(-1)),
+ Succeeds(0));
+}
+
+TEST_F(LlvmLibcLchownTest, LchownSuccessSymlink) {
+ uid_t my_uid = LIBC_NAMESPACE::getuid();
+ gid_t my_gid = LIBC_NAMESPACE::getgid();
+ constexpr const char *TARGET_FILENAME = "lchown_target.test";
+ constexpr const char *LINK_FILENAME = "lchown_symlink.test";
+ auto TARGET_FILE = libc_make_test_file_path(TARGET_FILENAME);
+ auto LINK_FILE = libc_make_test_file_path(LINK_FILENAME);
+
+ int write_fd = LIBC_NAMESPACE::open(TARGET_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+ ASSERT_ERRNO_SUCCESS();
+ ASSERT_GT(write_fd, 0);
+ ASSERT_THAT(LIBC_NAMESPACE::close(write_fd), Succeeds(0));
+
+ LIBC_NAMESPACE::cpp::scope_exit cleanup_target(
+ [&] { EXPECT_THAT(LIBC_NAMESPACE::unlink(TARGET_FILE), Succeeds(0)); });
+
+ // Create a symbolic link to the target file.
+ ASSERT_THAT(LIBC_NAMESPACE::symlink(TARGET_FILE, LINK_FILE), Succeeds(0));
+
+ LIBC_NAMESPACE::cpp::scope_exit cleanup_link(
+ [&] { EXPECT_THAT(LIBC_NAMESPACE::unlink(LINK_FILE), Succeeds(0)); });
+
+ // lchown should operate on the symbolic link itself.
+ ASSERT_THAT(LIBC_NAMESPACE::lchown(LINK_FILE, my_uid, my_gid), Succeeds(0));
+
+ // Passing -1 for owner and group leaves them unchanged without error.
+ ASSERT_THAT(LIBC_NAMESPACE::lchown(LINK_FILE, static_cast<uid_t>(-1),
+ static_cast<gid_t>(-1)),
+ Succeeds(0));
+}
+
+TEST_F(LlvmLibcLchownTest, LchownNonExistentFile) {
+ auto BAD_PATH = libc_make_test_file_path("non_existent_file_lchown.test");
+ ASSERT_THAT(LIBC_NAMESPACE::lchown(BAD_PATH, 1000, 1000), Fails(ENOENT));
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/230851
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