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/share/man/man9/VOP_LOCK.9

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  1.\" -*- nroff -*-
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  3.\" Copyright (c) 1996 Doug Rabson
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 29.\" $FreeBSD$
 30.\"
 31.Dd February 25, 2008
 32.Dt VOP_LOCK 9
 33.Os
 34.Sh NAME
 35.Nm VOP_LOCK ,
 36.Nm VOP_UNLOCK ,
 37.Nm VOP_ISLOCKED ,
 38.Nm vn_lock
 39.Nd serialize access to a vnode
 40.Sh SYNOPSIS
 41.In sys/param.h
 42.In sys/lock.h
 43.In sys/vnode.h
 44.Ft int
 45.Fn VOP_LOCK "struct vnode *vp" "int flags"
 46.Ft int
 47.Fn VOP_UNLOCK "struct vnode *vp" "int flags"
 48.Ft int
 49.Fn VOP_ISLOCKED "struct vnode *vp"
 50.Ft int
 51.Fn vn_lock "struct vnode *vp" "int flags"
 52.Sh DESCRIPTION
 53These calls are used to serialize access to the file system, such as
 54to prevent two writes to the same file from happening at the
 55same time.
 56.Pp
 57The arguments are:
 58.Bl -tag -width flags
 59.It Fa vp
 60The vnode being locked or unlocked.
 61.It Fa flags
 62One of the lock request types:
 63.Pp
 64.Bl -tag -width ".Dv LK_CANRECURSE" -offset indent -compact
 65.It Dv LK_SHARED
 66Shared lock.
 67.It Dv LK_EXCLUSIVE
 68Exclusive lock.
 69.It Dv LK_UPGRADE
 70Shared-to-exclusive upgrade.
 71.It Dv LK_DOWNGRADE
 72Exclusive-to-shared downgrade.
 73.It Dv LK_RELEASE
 74Release any type of lock.
 75.It Dv LK_DRAIN
 76Wait for all lock activity to end.
 77.El
 78.Pp
 79The lock type may be
 80.Em or Ns 'ed
 81with these lock flags:
 82.Pp
 83.Bl -tag -width ".Dv LK_CANRECURSE" -offset indent -compact
 84.It Dv LK_NOWAIT
 85Do not sleep to wait for lock.
 86.It Dv LK_SLEEPFAIL
 87Sleep, then return failure.
 88.It Dv LK_CANRECURSE
 89Allow recursive exclusive lock.
 90.It Dv LK_NOWITNESS
 91Instruct
 92.Xr witness 4
 93to ignore this instance.
 94.El
 95.Pp
 96The lock type may be
 97.Em or Ns 'ed
 98with these control flags:
 99.Pp
100.Bl -tag -width ".Dv LK_CANRECURSE" -offset indent -compact
101.It Dv LK_INTERLOCK
102Specify when the caller already has a simple lock
103.Fn ( VOP_LOCK
104will unlock the simple lock after getting the lock).
105.It Dv LK_RETRY
106Retry until locked.
107.El
108.Pp
109Kernel code should use
110.Fn vn_lock
111to lock a vnode rather than calling
112.Fn VOP_LOCK
113directly.
114.Fn vn_lock
115also does not want a thread specified as argument but it
116assumes curthread to be used.
117.El
118.Sh RETURN VALUES
119Zero is returned on success, otherwise an error is returned.
120.Sh SEE ALSO
121.Xr vnode 9
122.Sh AUTHORS
123This manual page was written by
124.An Doug Rabson .