ioctl_pipe.2: Add page.

Signed-off-by Cyril Hrubis <[email protected]>

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+.\" Copyright (c) 2022 by Cyril Hrubis <[email protected]>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.TH IOCTL_PIPE 2 2022-08-06 "Linux" "Linux Programmer's Manual"
+.SH NAME
+ioctl_pipe \- ioctl() operations for General notification mechanism
+.SH SYNOPSIS
+.nf
+.B #include <linux/watch_queue.h>
+.PP
+.BI "int ioctl(int " pipefd[1] ", IOC_WATCH_QUEUE_SET_SIZE, int " size ");
+.BI "int ioctl(int " pipefd[1] ", IOC_WATCH_QUEUE_SET_FILTER, \
+struct watch_notification_filter * " filter ");
+.fi
+.SH DESCRIPTION
+The following
+.BR ioctl (2)
+operations are provided to set up general notification queue parameters.
+The notification queue is build on the top of a
+.BR pipe (2)
+opened with the
+.B O_NOTIFICATION_PIPE
+flag.
+.TP
+.BR IOC_WATCH_QUEUE_SET_SIZE " (since Linux 5.8)"
+.\" commit c73be61cede5882f9605a852414db559c0ebedfd
+Preallocates the pipe buffer memory so that it can fit size notification
+messages. Currently the size must be between 1 and 512.
+.TP
+.BR IOC_WATCH_QUEUE_SET_FILTER " (since Linux 5.8)"
+.\" commit c73be61cede5882f9605a852414db559c0ebedfd
+Watch queue filter can limit events that are received. Filters are passed in a
+.I struct watch_notification_filter
+and each filter is described by
+.I struct watch_notification_type_filter
+structure.
+.PP
+.EX
+struct watch_notification_filter {
+        __u32   nr_filters;
+        __u32   __reserved;
+        struct watch_notification_type_filter filters[];
+};
+
+struct watch_notification_type_filter {
+        __u32   type;
+        __u32   info_filter;
+        __u32   info_mask;
+        __u32   subtype_filter[8];
+};
+.EE
+.PP
+.SH SEE ALSO
+.BR pipe (2),
+.BR ioctl (2)