.\" $OpenBSD: usbd_ref_wait.9,v 1.3 2016/06/30 19:54:13 mglocker Exp $
.\"
.\" Copyright (c) 2016 Marcus Glocker <mglocker@openbsd.org>
.\"
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.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.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