lib/libsys, lib/libc: export pdwait

Make pdwait(2) cancellable, same as all other wait*(2) syscalls wrappers.

Reviewed by:	asomers, markj
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D54592

lib/libc/include/libc_private.h

@@ -252,6 +252,7 @@ enum {
 	INTERPOS__reserved0, /* was distribute_static_tls */
 	INTERPOS_pdfork,
 	INTERPOS_uexterr_gettext,
+	INTERPOS_pdwait,
 	INTERPOS_MAX
 };
 

lib/libc/sys/Symbol.map

@@ -71,3 +71,7 @@ FBSD_1.6 {
 FBSD_1.7 {
 	_Fork;
 };
+
+FBSD_1.9 {
+	pdwait;
+};

lib/libc/sys/pdwait.c

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2026 The FreeBSD Foundation.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * This software was developed by Konstantin Belousov <kib@FreeBSD.org>
+ * under sponsorship from the FreeBSD Foundation.
+ */
+
+#include <sys/types.h>
+#include <sys/procdesc.h>
+#include "libc_private.h"
+
+#pragma weak pdwait
+int
+pdwait(int fd, int *status, int options, struct __wrusage *ru,
+    struct __siginfo *infop)
+{
+	return (INTERPOS_SYS(pdwait, fd, status, options, ru, infop));
+}

lib/libsys/Makefile.sys

@@ -73,6 +73,7 @@ INTERPOSED = \
 	open \
 	openat \
 	pdfork \
+	pdwait \
 	poll \
 	ppoll \
 	pselect \

lib/libsys/interposing_table.c

@@ -72,6 +72,7 @@ static interpos_func_t __libsys_interposing[INTERPOS_MAX] = {
 	SLOT(fdatasync, __sys_fdatasync),
 	SLOT(clock_nanosleep, __sys_clock_nanosleep),
 	SLOT(pdfork, __sys_pdfork),
+	SLOT(pdwait, __sys_pdwait),
 };
 #undef SLOT
 

lib/libthr/thread/thr_syscalls.c

@@ -584,6 +584,20 @@ __thr_wait6(idtype_t idtype, id_t id, int *status, int options,
 	return (ret);
 }
 
+static pid_t
+__thr_pdwait(int fd, int *status, int options, struct __wrusage *ru,
+    siginfo_t *infop)
+{
+	struct pthread *curthread;
+	pid_t ret;
+
+	curthread = _get_curthread();
+	_thr_cancel_enter(curthread);
+	ret = __sys_pdwait(fd, status, options, ru, infop);
+	_thr_cancel_leave(curthread, ret == -1);
+	return (ret);
+}
+
 /*
  * Cancellation behavior:
  *   Thread may be canceled at start, but if the thread wrote some data,
@@ -685,6 +699,7 @@ __thr_interpose_libc(void)
 	SLOT(clock_nanosleep);
 	SLOT(pdfork);
 	SLOT(uexterr_gettext);
+	SLOT(pdwait);
 #undef SLOT
 	*(__libc_interposing_slot(
 	    INTERPOS__pthread_mutex_init_calloc_cb)) =

sys/sys/procdesc.h

@@ -122,10 +122,14 @@ struct rusage;
  * Process descriptor system calls.
  */
 __BEGIN_DECLS
+struct __wrusage;
+struct __siginfo;
+
 pid_t	 pdfork(int *, int);
 pid_t	 pdrfork(int *, int, int);
 int	 pdkill(int, int);
 int	 pdgetpid(int, pid_t *);
+int	 pdwait(int, int *, int, struct __wrusage *, struct __siginfo *);
 __END_DECLS
 
 #endif /* _KERNEL */