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.\" $FreeBSD: src/share/man/man9/VFS_LOCK_GIANT.9,v 1.5.10.1.6.1 2010/12/21 17:09:25 kensmith Exp $
.\"
.Dd September 21, 2005
.Dt VFS_LOCK_GIANT 9
.Os
.Sh NAME
.Nm VFS_LOCK_GIANT ,
.Nm VFS_UNLOCK_GIANT
.Nd "conditionally lock and unlock Giant around entry into VFS"
.Sh SYNOPSIS
.In sys/param.h
.In sys/mount.h
.In sys/vnode.h
.Ft int
.Fn VFS_LOCK_GIANT "struct mount *mp"
.Ft void
.Fn VFS_UNLOCK_GIANT "int vfslocked"
.Sh DESCRIPTION
.Fn VFS_LOCK_GIANT
will conditionally acquire the
.Va Giant
lock if the file system referenced by
.Fa mp
is marked as MPSAFE or not, returning a flag indicating whether
.Va Giant
was
set, which may later be passed to
.Fn VFS_UNLOCK_GIANT .
The value of
.Fa mp
will typically be derived from the mount pointer in a
.Vt vnode
on which a VFS operation will be performed.
.Pp
.Fn VFS_UNLOCK_GIANT
conditionally releases the
.Va Giant
lock if the passed
.Fa vfslocked
argument is non-zero.
It is expected that the argument will be derived from the return values of
.Fn VFS_LOCK_GIANT
or
.Xr NDHASGIANT 9 .
.Sh RETURN VALUES
.Fn VFS_LOCK_GIANT
returns a boolean indicating whether or not
.Va Giant
was acquired.
.Sh SEE ALSO
.Xr mutex 9 ,
.Xr NDHASGIANT 9 ,
.Xr vnode 9
.Sh AUTHORS
.An -nosplit
MPSAFE VFS support for
.Fx
was implemented by
.An Jeff Roberson .
.Pp
This manual page was written by
.An Robert Watson .
.Sh BUGS
Non-MPSAFE file systems exist, requiring callers conditional locking and
unlocking of
.Va Giant .