Add wrappers for pidfd_{open,getfd,send_signal}.
Bug: http://b/172518739
Test: `/data/nativetest64/bionic-unit-tests/bionic-unit-tests --gtest_filter="*pidfd*"` on blueline
Change-Id: Ibae32bbedbcf26535a80a5cbfb55ce180906b610
diff --git a/libc/include/sys/pidfd.h b/libc/include/sys/pidfd.h
new file mode 100644
index 0000000..6d0e809
--- /dev/null
+++ b/libc/include/sys/pidfd.h
@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+#pragma once
+
+/**
+ * @file sys/pidfd.h
+ * @brief File descriptors representing processes.
+ */
+
+#include <sys/cdefs.h>
+#include <sys/types.h>
+
+#include <bits/signal_types.h>
+
+__BEGIN_DECLS
+
+/**
+ * [pidfd_open(2)](https://man7.org/linux/man-pages/man2/pidfd_open.2.html)
+ * opens a file descriptor that refers to a process. This file descriptor will
+ * have the close-on-exec flag set by default.
+ *
+ * Returns a new file descriptor on success and returns -1 and sets `errno` on
+ * failure.
+ *
+ * Available since API level 31.
+ */
+int pidfd_open(pid_t __pid, unsigned int __flags) __INTRODUCED_IN(31);
+
+/**
+ * [pidfd_getfd(2)](https://man7.org/linux/man-pages/man2/pidfd_open.2.html)
+ * dups a file descriptor from another process. This file descriptor will have
+ * the close-on-exec flag set by default.
+ *
+ * Returns a new file descriptor on success and returns -1 and sets `errno` on
+ * failure.
+ *
+ * Available since API level 31.
+ */
+int pidfd_getfd(int __pidfd, int __targetfd, unsigned int __flags) __INTRODUCED_IN(31);
+
+/**
+ * [pidfd_send_signal(2)](https://man7.org/linux/man-pages/man2/pidfd_send_signal.2.html)
+ * sends a signal to another process.
+ *
+ * Returns 0 on success and returns -1 and sets `errno` on failure.
+ *
+ * Available since API level 31.
+ */
+int pidfd_send_signal(int __pidfd, int __sig, siginfo_t *__info, unsigned int __flags) __INTRODUCED_IN(31);
+
+__END_DECLS