man: add man page for IORING_OP_WAITID

Signed-off-by: 李通洲 <zhangsongcui3371@sina.com>

man/io_uring_enter.2

@@ -1242,6 +1242,22 @@ for details on how to setup a context for fixed buffer I/O.
 .in
 .PP
 
+.TP
+.B IORING_OP_WAITID
+Issue the equivalent of a
+.BR waitid(2)
+system call.
+.I len
+must contain the idtype being queried/waited for and
+.I fd
+must contain the 'pid' (or id) being waited for.
+.I file_index
+is the 'options' being set (the child state changes to wait for).
+.I addr2
+is a pointer to siginfo_t, if any, being filled in. See also
+.BR waitid(2)
+for the general description of the related system call. Available since 6.5.
+
 .PP
 The
 .I flags

man/io_uring_prep_waitid.3

@@ -0,0 +1,60 @@
+.\" Copyright (C) 2022 Jens Axboe <axboe@kernel.dk>
+.\"
+.\" SPDX-License-Identifier: LGPL-2.0-or-later
+.\"
+.TH io_uring_prep_waitid 3 "July 14, 2023" "liburing-2.5" "liburing Manual"
+.SH NAME
+io_uring_prep_waitid \- prepare a waitid request
+.SH SYNOPSIS
+.nf
+.B #include <sys/wait.h>
+.B #include <liburing.h>
+.PP
+.BI "void io_uring_prep_waitid(struct io_uring_sqe *" sqe ","
+.BI "                          idtype_t " idtype ","
+.BI "                          id_t " id ","
+.BI "                          siginfo_t *" infop ","
+.BI "                          int " options ");"
+.fi
+.SH DESCRIPTION
+.PP
+The
+.BR io_uring_prep_waitid (3)
+function prepares a waitid request. The submission queue entry
+.I sqe
+is setup to use the
+.I idtype
+and
+.I id
+arguments select the child(ren), and
+.I options
+to specify the child state changes to wait for. Upon successful
+return, it fills
+.I infop
+with information of the child process, if any.
+
+This function prepares an async
+.BR waitid (2)
+request. See that man page for details.
+
+.SH RETURN VALUE
+None
+.SH ERRORS
+The CQE
+.I res
+field will contain the result of the operation. See the related man page for
+details on possible values. Note that where synchronous system calls will return
+.B -1
+on failure and set
+.I errno
+to the actual error value, io_uring never uses
+.IR errno .
+Instead it returns the negated
+.I errno
+directly in the CQE
+.I res
+field.
+.SH SEE ALSO
+.BR io_uring_get_sqe (3),
+.BR io_uring_submit (3),
+.BR waitid (2)