.\" Copyright (C) 2026 Yitang Yang <yi1tang.yang@gmail.com>
.\"
.\" SPDX-License-Identifier: LGPL-2.0-or-later
.\"
.TH io_uring_register_zcrx_ctrl 3 "March 26, 2026" "liburing-2.15" "liburing Manual"
.SH NAME
io_uring_register_zcrx_ctrl \- perform control operations on a zero-copy receive context
.SH SYNOPSIS
.nf
.B #include <liburing.h>
.PP
.BI "int io_uring_register_zcrx_ctrl(struct io_uring *" ring ","
.BI "                                struct zcrx_ctrl *" ctrl ");"
.fi
.SH DESCRIPTION
.PP
The
.BR io_uring_register_zcrx_ctrl (3)
function performs control operations on a previously registered zero-copy
receive context. See
.BR io_uring_register_ifq (3)
for details on registering a zero-copy receive context.

The
.I ctrl
argument must point to a
.I struct zcrx_ctrl
structure that describes the control operation to perform:

.PP
.in +4n
.EX
struct zcrx_ctrl {
    __u32 zcrx_id;
    __u32 op;
    __u64 __resv[2];
    union {
        struct zcrx_ctrl_export     zc_export;
        struct zcrx_ctrl_flush_rq   zc_flush;
    };
};
.EE
.in
.PP

The
.I zcrx_id
field must be set to the ID of the zero-copy receive context returned from
.BR io_uring_register_ifq (3).
The
.I op
field specifies the control operation to perform and can be one of:

.TP
.B ZCRX_CTRL_FLUSH_RQ
Flushes pending buffers from the refill queue. Uses the
.I zc_flush
member of the union.

.TP
.B ZCRX_CTRL_EXPORT
Exports the zero-copy receive context for use by other rings. Uses the
.I zc_export
member of the union. Upon successful export, the
.I zcrx_fd
field in
.I zc_export
will contain the file descriptor that can be used to share this context
with other io_uring instances.

.PP
The reserved
.I __resv
fields must be cleared to zero.

.SH RETURN VALUE
Returns 0 on success. On error, a negative errno value is returned.

.SH NOTES
This function is available since Linux kernel 6.15.

.SH SEE ALSO
.BR io_uring_register (2),
.BR io_uring_register_ifq (3)