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.\" Copyright (c) 2000 Boris Popov
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.Dd September 10, 2000
.Dt VOP_CREATEVOBJECT 9
.Os
.Sh NAME
.Nm VOP_CREATEVOBJECT ,
.Nm VOP_DESTROYVOBJECT ,
.Nm VOP_GETVOBJECT
.Nd VM object interaction
.Sh SYNOPSIS
.In sys/param.h
.In sys/vnode.h
.Ft int
.Fn VOP_CREATEVOBJECT "struct vnode *vp" "struct ucred *cred" "struct thread *td"
.Ft int
.Fn VOP_DESTROYVOBJECT "struct vnode *vp"
.Ft int
.Fn VOP_GETVOBJECT "struct vnode *vp" "struct vm_object **objpp"
.Sh DESCRIPTION
These calls are used to control the association of a VM object
with a particular vnode.
.Pp
The arguments specific to these functions are:
.Bl -tag -width objpp
.It Fa vp
The vnode of the file.
.It Fa objpp
The VM object being returned, or
.Dv NULL
if the caller wants to test for the existence
of the VM object.
.El
.Pp
.Xr VFS 9
invokes
.Fn VOP_CREATEVOBJECT
when it needs to create a VM object for the given
.Xr vnode 9 .
File system code may pass this call down to the underlying file system.
This VOP can be called multiple times,
and file system code should ignore any additional calls,
exiting with a zero return code.
.Pp
.Fn VOP_DESTROYVOBJECT
is called when a
.Xr vnode 9
is recycled.
.Pp
.Fn VOP_GETVOBJECT
should be used by all kernel code to get a VM object.
.\" XXX What is the next sentence trying to tell people?
The returned VM object may belong to a different file system in the case
of stacked mounts.
.Pp
.Xr VFS 9
has three functions which perform standard operations by creating
and destroying VM objects.
These functions are:
.Fn vop_stdcreatevobject ,
.Fn vop_stddestroyvobject
and
.Fn vop_stdgetvobject .
.Pp
.Em Note :
a
.Xr vnode 9
should be locked on entry and must be left locked on exit.
.Sh RETURN VALUES
The
.Fn VOP_CREATEVOBJECT ,
.Fn VOP_DESTROYVOBJECT
and
.Fn VOP_GETVOBJECT
functions return zero on success, or a non-zero value on failure.
Zero is returned on success, otherwise an error is returned.
.Sh EXAMPLES
.\" XXX Why is this code here when it does not use the functions
.\" described in this manual page?
By default, file systems leave VM object handling to the
.Fn vop_std*
functions.
.Sh SEE ALSO
.Xr vnode 9 ,
.Xr VOP_GETPAGES 9 ,
.Xr VOP_PUTPAGES 9
.Sh AUTHORS
This manual page was written by
.An Boris Popov .