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freebsd/share/man/man9/VFS_LOCK_GIANT.9
Robert Watson fdd3cfa0aa Back out VFS_LOCK_GIANT.9:1.4, due to losing a race in change/update
against revision 1.3.  No need to include mount.h twice, once will be
quite enough.

Pointed out by:	simon
2006-01-03 14:00:22 +00:00

94 lines
2.8 KiB
Groff

.\"
.\" Copyright (c) 2005 Robert N. M. Watson
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.\" $FreeBSD$
.\"
.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 .