xref: /freebsd/share/man/man9/VOP_LOCK.9 (revision fe166a35ff0c70708abd1bac2153063f2828fa35)

.\" -*- nroff -*-
.\"
.\" Copyright (c) 1996 Doug Rabson
.\"
.\" All rights reserved.
.\"
.\" This program is free software.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd January 10, 2008
.Os
.Dt VOP_LOCK 9
.Sh NAME
.Nm VOP_LOCK ,
.Nm VOP_UNLOCK ,
.Nm VOP_ISLOCKED ,
.Nm vn_lock
.Nd serialize access to a vnode
.Sh SYNOPSIS
.In sys/param.h
.In sys/lock.h
.In sys/vnode.h
.Ft int
.Fn VOP_LOCK "struct vnode *vp" "int flags" "struct thread *td"
.Ft int
.Fn VOP_UNLOCK "struct vnode *vp" "int flags" "struct thread *td"
.Ft int
.Fn VOP_ISLOCKED "struct vnode *vp" "struct thread *td"
.Ft int
.Fn vn_lock "struct vnode *vp" "int flags"
.Sh DESCRIPTION
These calls are used to serialize access to the file system, such as
to prevent two writes to the same file from happening at the
same time.
.Pp
The arguments are:
.Bl -tag -width flags
.It Fa vp
The vnode being locked or unlocked.
.It Fa flags
One of the lock request types:
.Pp
.Bl -tag -width ".Dv LK_CANRECURSE" -offset indent -compact
.It Dv LK_SHARED
Shared lock.
.It Dv LK_EXCLUSIVE
Exclusive lock.
.It Dv LK_UPGRADE
Shared-to-exclusive upgrade.
.It Dv LK_DOWNGRADE
Exclusive-to-shared downgrade.
.It Dv LK_RELEASE
Release any type of lock.
.It Dv LK_DRAIN
Wait for all lock activity to end.
.El
.Pp
The lock type may be
.Em or Ns 'ed
with these lock flags:
.Pp
.Bl -tag -width ".Dv LK_CANRECURSE" -offset indent -compact
.It Dv LK_NOWAIT
Do not sleep to wait for lock.
.It Dv LK_SLEEPFAIL
Sleep, then return failure.
.It Dv LK_CANRECURSE
Allow recursive exclusive lock.
.El
.Pp
The lock type may be
.Em or Ns 'ed
with these control flags:
.Pp
.Bl -tag -width ".Dv LK_CANRECURSE" -offset indent -compact
.It Dv LK_INTERLOCK
Specify when the caller already has a simple lock
.Fn ( VOP_LOCK
will unlock the simple lock after getting the lock).
.It Dv LK_RETRY
Retry until locked.
.El
.It Fa td
Thread context to use for the locks.
.El
.Pp
Kernel code should use
.Fn vn_lock
to lock a vnode rather than calling
.Fn VOP_LOCK
directly.
.Fn vn_lock
also doesn't want a thread specified as argument but it
assumes curthread to be used.
.Sh RETURN VALUES
Zero is returned on success, otherwise an error is returned.
.Sh PSEUDOCODE
.Bd -literal
struct vopnode {
    int von_flag;
    /*
     * Other file system specific data.
     */
    ...;
};
#define VON_LOCKED	1
#define VON_WANTED	2
#define VTOVON(vp)	((struct vopnode *) (vp)->v_data)

int
vop_lock(struct vnode *vp)
{
    struct vopnode* vop;

start:
    while (vp->v_flag & VXLOCK) {
	vp->v_flag |= VXWANT;
	tsleep((caddr_t)vp, PINOD, "voplk1", 0);
    }
    if (vp->v_tag == VT_NON)
	return ENOENT;

    vop = VTOVON(vp);
    if (vop->von_flag & VON_LOCKED) {
	vop->von_flag |= VON_WANTED;
	tsleep((caddr_t) vop, PINOD, "voplk2", 0);
	goto start;
    }

    vop->von_flag |= VON_LOCKED;

    return 0;
}

int
vop_unlock(struct vnode *vp)
{
    struct vopnode *vop = VTOVON(vp);

    if ((vop->von_flag & VON_LOCKED) == 0) {
	panic("vop_unlock not locked");
    }
    vop->von_flag &= ~VON_LOCKED;
    if (vop->von_flag & VON_WANTED) {
	vop->von_flag &= ~VON_WANTED;
	wakeup((caddr_t) vop);
    }

    return 0;
}

int
vop_islocked(struct vnode *vp)
{
    struct vopnode *vop = VTOVON(vp);

    if (vop->von_flag & VON_LOCKED)
	return 1;
    else
	return 0;
}
.Ed
.Sh SEE ALSO
.Xr vnode 9
.Sh AUTHORS
This manual page was written by
.An Doug Rabson .