Document dev_clone eventhandler interface

share/man/man9/dev_clone.9

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+.\" Copyright (c) 2008 Konstantin Belousov
+.\" All rights reserved.
+.\"
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+.\" $FreeBSD$
+.\"
+.Dd September 8, 2008
+.Sh NAME
+.Nm dev_clone ,
+.Nm drain_dev_clone_events
+.Nd eventhandler for name-based device cloning in devfs
+.Sh SYNOPSIS
+.In sys/param.h
+.In sys/conf.h
+.Ft void
+.Fn clone_handler "void *arg" "struct ucred *cr" "char *name" "int namelen" "struct cdev **dev"
+.Bd -literal
+EVENTHANDLER_REGISTER(dev_clone, clone_handler, arg, priority);
+.Ed
+.Ft void
+.Fn drain_dev_clone_events
+.Sh DESCRIPTION
+Device driver may register a listener that will be notified each time
+name lookup on the
+.Xr devfs
+mount point fails to find the vnode.
+Listener shall be registered for the
+.Va dev_clone
+event.
+When called, it is supplied with the first argument
+.Va arg
+that was specified at handler registration time,
+appropriate credentials
+.Va cr ,
+.Va name
+of the length
+.Va namelen
+that was looked for.
+If handler decides that the name is appropriate and want to create device
+that will be associated with the name, it should return it to the devfs
+in the
+.Va dev .
+.Pp
+The
+.Fn drain_dev_clone_events
+function is a barrier.
+It is guaranteed that all calls to eventhandlers for dev_clone that were
+started before
+.Fn drain_dev_clone_events
+call, are finished before it returns control.
+.Pp
+.Sh SEE ALSO
+.Xr devfs 5 ,
+.Xr namei 9