[libc-commits] [libc] Implement linux-specific sendmmsg(2) (PR #198778)
Pavel Labath via libc-commits
libc-commits at lists.llvm.org
Wed May 20 06:20:49 PDT 2026
https://github.com/labath created https://github.com/llvm/llvm-project/pull/198778
Assisted by Gemini.
>From ada48c696134e354a59fa8217adee18a062c428a Mon Sep 17 00:00:00 2001
From: Pavel Labath <pavel at labath.sk>
Date: Tue, 19 May 2026 14:30:02 +0000
Subject: [PATCH] Implement linux-specific sendmmsg(2)
Assisted by Gemini.
---
libc/config/linux/aarch64/entrypoints.txt | 1 +
libc/config/linux/riscv/entrypoints.txt | 1 +
libc/config/linux/x86_64/entrypoints.txt | 1 +
libc/hdr/types/CMakeLists.txt | 9 ++
libc/hdr/types/struct_mmsghdr.h | 26 ++++++
libc/include/llvm-libc-types/CMakeLists.txt | 1 +
libc/include/llvm-libc-types/struct_mmsghdr.h | 24 ++++++
libc/include/sys/socket.yaml | 10 +++
.../linux/syscall_wrappers/CMakeLists.txt | 13 +++
.../OSUtil/linux/syscall_wrappers/sendmmsg.h | 35 ++++++++
libc/src/sys/socket/CMakeLists.txt | 7 ++
libc/src/sys/socket/linux/CMakeLists.txt | 13 +++
libc/src/sys/socket/linux/sendmmsg.cpp | 32 +++++++
libc/src/sys/socket/sendmmsg.h | 26 ++++++
libc/test/src/sys/socket/linux/CMakeLists.txt | 20 +++++
.../src/sys/socket/linux/sendmmsg_test.cpp | 84 +++++++++++++++++++
libc/utils/docgen/sys/socket.yaml | 2 +
17 files changed, 305 insertions(+)
create mode 100644 libc/hdr/types/struct_mmsghdr.h
create mode 100644 libc/include/llvm-libc-types/struct_mmsghdr.h
create mode 100644 libc/src/__support/OSUtil/linux/syscall_wrappers/sendmmsg.h
create mode 100644 libc/src/sys/socket/linux/sendmmsg.cpp
create mode 100644 libc/src/sys/socket/sendmmsg.h
create mode 100644 libc/test/src/sys/socket/linux/sendmmsg_test.cpp
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index c7458ef36c941..f4b13ec300083 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -303,6 +303,7 @@ set(TARGET_LIBC_ENTRYPOINTS
# TODO: These functions are not compatible with 64-bit musl. They need to
# be excluded if overlaying musl.
libc.src.sys.socket.recvmsg
+ libc.src.sys.socket.sendmmsg
libc.src.sys.socket.sendmsg
# sys/stat.h entrypoints
diff --git a/libc/config/linux/riscv/entrypoints.txt b/libc/config/linux/riscv/entrypoints.txt
index e3336420cbbcc..32c4342f713aa 100644
--- a/libc/config/linux/riscv/entrypoints.txt
+++ b/libc/config/linux/riscv/entrypoints.txt
@@ -303,6 +303,7 @@ set(TARGET_LIBC_ENTRYPOINTS
# TODO: These functions are not compatible with 64-bit musl. They need to
# be excluded if overlaying musl.
libc.src.sys.socket.recvmsg
+ libc.src.sys.socket.sendmmsg
libc.src.sys.socket.sendmsg
# sys/stat.h entrypoints
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 3c3b0e835429f..641aba1a029fe 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -327,6 +327,7 @@ set(TARGET_LIBC_ENTRYPOINTS
# TODO: These functions are not compatible with 64-bit musl. They need to
# be excluded if overlaying musl.
libc.src.sys.socket.recvmsg
+ libc.src.sys.socket.sendmmsg
libc.src.sys.socket.sendmsg
# sys/stat.h entrypoints
diff --git a/libc/hdr/types/CMakeLists.txt b/libc/hdr/types/CMakeLists.txt
index 626c5fb82883e..09b6cc5b7fd9a 100644
--- a/libc/hdr/types/CMakeLists.txt
+++ b/libc/hdr/types/CMakeLists.txt
@@ -411,6 +411,15 @@ add_proxy_header_library(
libc.include.sys_socket
)
+add_proxy_header_library(
+ struct_mmsghdr
+ HDRS
+ struct_mmsghdr.h
+ FULL_BUILD_DEPENDS
+ libc.include.llvm-libc-types.struct_mmsghdr
+ libc.include.sys_socket
+)
+
add_proxy_header_library(
struct_msghdr
HDRS
diff --git a/libc/hdr/types/struct_mmsghdr.h b/libc/hdr/types/struct_mmsghdr.h
new file mode 100644
index 0000000000000..84473bbd46685
--- /dev/null
+++ b/libc/hdr/types/struct_mmsghdr.h
@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+/// Proxy for struct mmsghdr.
+///
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_LIBC_HDR_TYPES_STRUCT_MMSGHDR_H
+#define LLVM_LIBC_HDR_TYPES_STRUCT_MMSGHDR_H
+
+#ifdef LIBC_FULL_BUILD
+
+#include "include/llvm-libc-types/struct_mmsghdr.h"
+
+#else
+
+#include <sys/socket.h>
+
+#endif // LIBC_FULL_BUILD
+
+#endif // LLVM_LIBC_HDR_TYPES_STRUCT_MMSGHDR_H
diff --git a/libc/include/llvm-libc-types/CMakeLists.txt b/libc/include/llvm-libc-types/CMakeLists.txt
index 2904e0d07f76c..1bf09f5337a48 100644
--- a/libc/include/llvm-libc-types/CMakeLists.txt
+++ b/libc/include/llvm-libc-types/CMakeLists.txt
@@ -205,6 +205,7 @@ add_header(struct_iovec HDR struct_iovec.h DEPENDS .size_t)
add_header(struct_linger HDR struct_linger.h)
add_header(struct_cmsghdr HDR struct_cmsghdr.h DEPENDS .size_t)
add_header(struct_msghdr HDR struct_msghdr.h DEPENDS .size_t .socklen_t .struct_iovec)
+add_header(struct_mmsghdr HDR struct_mmsghdr.h DEPENDS .struct_msghdr)
add_header(ACTION HDR ACTION.h)
add_header(ENTRY HDR ENTRY.h)
add_header(VISIT HDR VISIT.h)
diff --git a/libc/include/llvm-libc-types/struct_mmsghdr.h b/libc/include/llvm-libc-types/struct_mmsghdr.h
new file mode 100644
index 0000000000000..8f4297d124a9b
--- /dev/null
+++ b/libc/include/llvm-libc-types/struct_mmsghdr.h
@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+/// Definition of struct mmsghdr.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_TYPES_STRUCT_MMSGHDR_H
+#define LLVM_LIBC_TYPES_STRUCT_MMSGHDR_H
+
+#include "struct_msghdr.h"
+
+struct mmsghdr {
+ struct msghdr msg_hdr; /* Message header */
+ unsigned int msg_len; /* Number of bytes sent/received */
+};
+
+#endif // LLVM_LIBC_TYPES_STRUCT_MMSGHDR_H
diff --git a/libc/include/sys/socket.yaml b/libc/include/sys/socket.yaml
index e5e9c9d2df183..900ce1f717e60 100644
--- a/libc/include/sys/socket.yaml
+++ b/libc/include/sys/socket.yaml
@@ -10,6 +10,7 @@ types:
- type_name: socklen_t
- type_name: sa_family_t
- type_name: struct_cmsghdr
+ - type_name: struct_mmsghdr
- type_name: struct_msghdr
- type_name: struct_iovec
- type_name: struct_linger
@@ -121,6 +122,15 @@ functions:
- type: const void*
- type: size_t
- type: int
+ - name: sendmmsg
+ standards:
+ - Linux
+ return_type: int
+ arguments:
+ - type: int
+ - type: struct mmsghdr *
+ - type: unsigned int
+ - type: int
- name: sendmsg
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 dc1702e1e4539..1673f92a2c57b 100644
--- a/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt
+++ b/libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt
@@ -189,6 +189,19 @@ add_header_library(
libc.include.sys_syscall
)
+add_header_library(
+ sendmmsg
+ HDRS
+ sendmmsg.h
+ DEPENDS
+ libc.src.__support.OSUtil.osutil
+ libc.src.__support.common
+ libc.src.__support.error_or
+ libc.src.__support.macros.config
+ libc.hdr.types.struct_mmsghdr
+ libc.include.sys_syscall
+)
+
add_header_library(
sendmsg
HDRS
diff --git a/libc/src/__support/OSUtil/linux/syscall_wrappers/sendmmsg.h b/libc/src/__support/OSUtil/linux/syscall_wrappers/sendmmsg.h
new file mode 100644
index 0000000000000..3e943539303e0
--- /dev/null
+++ b/libc/src/__support/OSUtil/linux/syscall_wrappers/sendmmsg.h
@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 sendmmsg.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_SENDMMSG_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_SENDMMSG_H
+
+#include "hdr/types/struct_mmsghdr.h"
+#include "src/__support/OSUtil/linux/syscall.h" // For 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> sendmmsg(int sockfd, struct mmsghdr *msgvec,
+ unsigned int vlen, int flags) {
+ return syscall_checked<int>(SYS_sendmmsg, sockfd, msgvec, vlen, flags);
+}
+
+} // namespace linux_syscalls
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_SENDMMSG_H
diff --git a/libc/src/sys/socket/CMakeLists.txt b/libc/src/sys/socket/CMakeLists.txt
index a100e90fe3f2d..22b665392a4d6 100644
--- a/libc/src/sys/socket/CMakeLists.txt
+++ b/libc/src/sys/socket/CMakeLists.txt
@@ -93,6 +93,13 @@ add_entrypoint_object(
.${LIBC_TARGET_OS}.setsockopt
)
+add_entrypoint_object(
+ sendmmsg
+ ALIAS
+ DEPENDS
+ .${LIBC_TARGET_OS}.sendmmsg
+)
+
add_entrypoint_object(
sendmsg
ALIAS
diff --git a/libc/src/sys/socket/linux/CMakeLists.txt b/libc/src/sys/socket/linux/CMakeLists.txt
index 4c7352dbd0200..b8ff28f94dd2c 100644
--- a/libc/src/sys/socket/linux/CMakeLists.txt
+++ b/libc/src/sys/socket/linux/CMakeLists.txt
@@ -180,6 +180,19 @@ add_entrypoint_object(
libc.src.errno.errno
)
+add_entrypoint_object(
+ sendmmsg
+ SRCS
+ sendmmsg.cpp
+ HDRS
+ ../sendmmsg.h
+ DEPENDS
+ libc.hdr.types.struct_mmsghdr
+ libc.src.__support.common
+ libc.src.__support.OSUtil.linux.syscall_wrappers.sendmmsg
+ libc.src.errno.errno
+)
+
add_entrypoint_object(
sendmsg
SRCS
diff --git a/libc/src/sys/socket/linux/sendmmsg.cpp b/libc/src/sys/socket/linux/sendmmsg.cpp
new file mode 100644
index 0000000000000..1181fea1f999e
--- /dev/null
+++ b/libc/src/sys/socket/linux/sendmmsg.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 sendmmsg.
+///
+//===----------------------------------------------------------------------===//
+#include "src/sys/socket/sendmmsg.h"
+#include "hdr/types/struct_mmsghdr.h"
+#include "src/__support/OSUtil/linux/syscall_wrappers/sendmmsg.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, sendmmsg,
+ (int sockfd, struct mmsghdr *msgvec, unsigned int vlen,
+ int flags)) {
+ auto result = linux_syscalls::sendmmsg(sockfd, msgvec, vlen, flags);
+ if (!result.has_value()) {
+ libc_errno = result.error();
+ return -1;
+ }
+ return result.value();
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/sys/socket/sendmmsg.h b/libc/src/sys/socket/sendmmsg.h
new file mode 100644
index 0000000000000..6701f6cacab43
--- /dev/null
+++ b/libc/src/sys/socket/sendmmsg.h
@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+/// Declaration of the sendmmsg function.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SYS_SOCKET_SENDMMSG_H
+#define LLVM_LIBC_SRC_SYS_SOCKET_SENDMMSG_H
+
+#include "hdr/types/struct_mmsghdr.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int sendmmsg(int sockfd, struct mmsghdr *msgvec, unsigned int vlen, int flags);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_SYS_SOCKET_SENDMMSG_H
diff --git a/libc/test/src/sys/socket/linux/CMakeLists.txt b/libc/test/src/sys/socket/linux/CMakeLists.txt
index 3b0c9748056cf..473a85502d55a 100644
--- a/libc/test/src/sys/socket/linux/CMakeLists.txt
+++ b/libc/test/src/sys/socket/linux/CMakeLists.txt
@@ -204,6 +204,26 @@ add_libc_unittest(
libc.test.UnitTest.ErrnoSetterMatcher
)
+add_libc_unittest(
+ sendmmsg_test
+ SUITE
+ libc_sys_socket_unittests
+ SRCS
+ sendmmsg_test.cpp
+ DEPENDS
+ libc.hdr.sys_socket_macros
+ libc.hdr.types.struct_mmsghdr
+ libc.src.errno.errno
+ libc.src.string.strlen
+ libc.src.sys.socket.socketpair
+ libc.src.sys.socket.sendmmsg
+ libc.src.sys.socket.recvmsg
+ libc.src.unistd.close
+ libc.src.__support.CPP.scope
+ libc.test.UnitTest.ErrnoCheckingTest
+ libc.test.UnitTest.ErrnoSetterMatcher
+)
+
add_libc_unittest(
sendmsg_recvmsg_test
SUITE
diff --git a/libc/test/src/sys/socket/linux/sendmmsg_test.cpp b/libc/test/src/sys/socket/linux/sendmmsg_test.cpp
new file mode 100644
index 0000000000000..adbfe20205b8f
--- /dev/null
+++ b/libc/test/src/sys/socket/linux/sendmmsg_test.cpp
@@ -0,0 +1,84 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+/// Unit tests for sendmmsg.
+///
+//===----------------------------------------------------------------------===//
+
+#include "hdr/sys_socket_macros.h"
+#include "hdr/types/struct_mmsghdr.h"
+#include "src/__support/CPP/scope.h"
+#include "src/string/strlen.h"
+#include "src/sys/socket/recvmsg.h"
+#include "src/sys/socket/sendmmsg.h"
+#include "src/sys/socket/socketpair.h"
+#include "src/unistd/close.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+#include "test/UnitTest/LibcTest.h"
+#include "test/UnitTest/Test.h"
+
+using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Fails;
+using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Succeeds;
+using LlvmLibcSendMmsgTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST_F(LlvmLibcSendMmsgTest, SendMmsgSucceedsWithSocketPair) {
+ const char *const TEST_MESSAGES[] = {"message one", "message two"};
+ const size_t MESSAGES_COUNT = 2;
+
+ int sockpair[2] = {0, 0};
+
+ ASSERT_THAT(LIBC_NAMESPACE::socketpair(AF_UNIX, SOCK_DGRAM, 0, sockpair),
+ Succeeds(0));
+ LIBC_NAMESPACE::cpp::scope_exit close_sockpair([&] {
+ ASSERT_THAT(LIBC_NAMESPACE::close(sockpair[0]), Succeeds(0));
+ ASSERT_THAT(LIBC_NAMESPACE::close(sockpair[1]), Succeeds(0));
+ });
+
+ struct iovec send_msg_vec[MESSAGES_COUNT] = {};
+ struct mmsghdr send_msg_hdr[MESSAGES_COUNT] = {};
+ for (size_t i = 0; i < MESSAGES_COUNT; ++i) {
+ send_msg_vec[i].iov_base =
+ reinterpret_cast<void *>(const_cast<char *>(TEST_MESSAGES[i]));
+ send_msg_vec[i].iov_len = LIBC_NAMESPACE::strlen(TEST_MESSAGES[i]) + 1;
+ send_msg_hdr[i].msg_hdr.msg_iov = &send_msg_vec[i];
+ send_msg_hdr[i].msg_hdr.msg_iovlen = 1;
+ }
+
+ ASSERT_THAT(
+ LIBC_NAMESPACE::sendmmsg(sockpair[0], send_msg_hdr, MESSAGES_COUNT, 0),
+ Succeeds(static_cast<int>(MESSAGES_COUNT)));
+
+ for (size_t i = 0; i < MESSAGES_COUNT; ++i) {
+ ASSERT_EQ(static_cast<size_t>(send_msg_hdr[i].msg_len),
+ LIBC_NAMESPACE::strlen(TEST_MESSAGES[i]) + 1);
+ }
+
+ for (size_t i = 0; i < MESSAGES_COUNT; ++i) {
+ char recv_buffer[256] = {};
+ struct iovec recv_msg_vec;
+ recv_msg_vec.iov_base = reinterpret_cast<void *>(recv_buffer);
+ recv_msg_vec.iov_len = sizeof(recv_buffer);
+
+ struct msghdr recv_msg_hdr = {};
+ recv_msg_hdr.msg_iov = &recv_msg_vec;
+ recv_msg_hdr.msg_iovlen = 1;
+
+ ASSERT_THAT(LIBC_NAMESPACE::recvmsg(sockpair[1], &recv_msg_hdr, 0),
+ Succeeds(static_cast<ssize_t>(
+ LIBC_NAMESPACE::strlen(TEST_MESSAGES[i]) + 1)));
+ ASSERT_STREQ(recv_buffer, TEST_MESSAGES[i]);
+ }
+}
+
+TEST_F(LlvmLibcSendMmsgTest, SendMmsgFails) {
+ struct mmsghdr msg_hdrs = {};
+
+ ASSERT_THAT(LIBC_NAMESPACE::sendmmsg(-1, &msg_hdrs, 1, 0), Fails(EBADF, -1));
+}
diff --git a/libc/utils/docgen/sys/socket.yaml b/libc/utils/docgen/sys/socket.yaml
index d0b8a7e087e70..1c9af64a76331 100644
--- a/libc/utils/docgen/sys/socket.yaml
+++ b/libc/utils/docgen/sys/socket.yaml
@@ -126,6 +126,8 @@ functions:
in-latest-posix: ''
send:
in-latest-posix: ''
+ sendmmsg:
+ c-definition: ''
sendmsg:
in-latest-posix: ''
sendto:
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