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.\" $OpenBSD: usbd_ref_wait.9,v 1.3 2016/06/30 19:54:13 mglocker Exp $
.\"
.\" Copyright (c) 2016 Marcus Glocker <mglocker@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: June 30 2016 $
.Dt USBD_REF_WAIT 9
.Os
.Sh NAME
.Nm usbd_ref_incr , usbd_ref_decr , usbd_ref_wait
.Nd wait for all USB device references to complete
.Sh SYNOPSIS
.In dev/usb/usb.h
.In dev/usb/usbdi.h
.Ft void
.Fn usbd_ref_incr "struct usbd_device *dev"
.Ft void
.Fn usbd_ref_decr "struct usbd_device *dev"
.Ft void
.Fn usbd_ref_wait "struct usbd_device *dev"
.Sh DESCRIPTION
The
.Fn usbd_ref_wait
function is used on a device level to
.Xr tsleep 9
until the reference counter has reached zero.
.Pp
To increase the reference counter use
.Fn usbd_ref_incr .
To decrease the reference counter use
.Fn usbd_ref_decr .
Once the reference counter has been decreased to zero,
.Fn usbd_ref_decr
will call
.Fn wakeup
to interrupt the
.Fn tsleep
at the point where
.Fn usbd_ref_wait
was previously set.
.Pp
Typical use cases to wait for tasks to complete is at device closing
or detachment.
.Sh CONTEXT
.Fn usbd_ref_incr ,
.Fn usbd_ref_decr ,
and
.Fn usbd_ref_wait
can be called during autoconf or from process context.
.Sh SEE ALSO
.Xr usb 4 ,
.Xr tsleep 9 ,
.Xr wakeup 9
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