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Add discussion of Giant, the MPSAFE flag, and NDHASGIANT() to namei(9).

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Add a VFS_LOCK_GIANT(9)/VFS_UNLOCK_GIANT(9) man page.

Discussed with:	jeff
MFC after:	3 days
This commit is contained in:
rwatson 2005-09-21 10:19:57 +00:00
parent 936ef077e7
commit 24f9041880
3 changed files with 124 additions and 1 deletions
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2
share/man/man9/Makefile
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@ -231,6 +231,7 @@ MAN= accept_filter.9 \
VFS_FHTOVP.9 \
vfs_getnewfsid.9 \
vfs_getvfs.9 \
VFS_LOCK_GIANT.9 \
VFS_MOUNT.9 \
vfs_mount.9 \
vfs_mountedon.9 \
@ -973,6 +974,7 @@ MLINKS+=vcount.9 count_dev.9
MLINKS+=vfsconf.9 vfs_modevent.9 \
vfsconf.9 vfs_register.9 \
vfsconf.9 vfs_unregister.9
MLINKS+=VFS_LOCK_GIANT.9 VFS_UNLOCK_GIANT.9
MLINKS+=vgone.9 vgonel.9
MLINKS+=vhold.9 vdrop.9
MLINKS+=vm_map_lock.9 vm_map_lock_downgrade.9 \

90
share/man/man9/VFS_LOCK_GIANT.9 Normal file
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@ -0,0 +1,90 @@
.\"
.\" Copyright (c) 2005 Robert N. M. Watson
.\" All rights reserved.
.\"
.\" 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(s), this list of conditions and the following disclaimer as
.\" the first lines of this file unmodified other than the possible
.\" addition of one or more copyright notices.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice(s), 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 COPYRIGHT HOLDER(S) ``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 COPYRIGHT HOLDER(S) 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 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/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
.Dv Giant
lock if the file system referenced by
.Fa mp
is marked as MPSAFE or not, returning a flag indicating whether 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
.Xr 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
.Vn 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
MPSAFE VFS support for
.Fx
was implemented by
.An Jeff Roberson .
.Pp
This manual page was written by
.An Robert Watson .
.Sh BUGS
.Pp
Non-MPSAFE file systems exist, requiring callers conditional locking and
unlocking of
.Va Giant .

33
share/man/man9/namei.9
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@ -1,6 +1,7 @@
.\"
.\" Copyright (c) 1998, 1999 Eivind Eklund
.\" Copyright (c) 2003 Hiten M. Pandya
.\" Copyright (c) 2005 Robert N. M. Watson
.\"
.\" All rights reserved.
.\"
@ -38,7 +39,8 @@
.Sh NAME
.Nm namei ,
.Nm NDINIT ,
.Nm NDFREE
.Nm NDFREE ,
.Nm NDHASGIANT
.Nd pathname translation and lookup operations
.Sh SYNOPSIS
.In sys/param.h
@ -53,6 +55,8 @@
.Fc
.Ft void
.Fn NDFREE "struct nameidata *ndp" "const uint flags"
.Ft int
.Fn NDHASGIANT "struct nameidata *ndp"
.Sh DESCRIPTION
The
.Nm
@ -69,6 +73,16 @@ or
depending on whether the
.Dv LOCKLEAF
flag was specified or not.
If the
.Va Giant
lock is required,
.Nm
will acquire it if the caller indicates it is
.Dv MPSAFE ,
in which case the caller must later release
.Va Giant
based on the results of
.Fn NDHASGIANT.
.Pp
The
.Fn NDINIT
@ -154,6 +168,19 @@ This flag allows the
function to return the parent (directory) vnode in an unlocked state.
The parent vnode must be released separately by using
.Xr vrele 9 .
.It Dv MPSAFE
With this flag set,
.Fn namei
will conditionally acquire
.Va Giant
if it is required by a traversed file system.
MPSAFE callers should pass the results of
.Fn NDHASGIANT
to
.Xr VFS_UNLOCK_GIANT
in order to conditionally release
.Va Giant
if necessary.
.It Dv NOCACHE
Avoid
.Fn namei
@ -296,6 +323,7 @@ function.
.Xr uio 9 ,
.Xr uma 9 ,
.Xr VFS 9 ,
.Xr VFS_UNLOCK_GIANT 9 ,
.Xr vnode 9 ,
.Xr vput 9 ,
.Xr vref 9
@ -317,3 +345,6 @@ In order to solve this for the cases where both
and
.Dv LOCKLEAF
are used, it is necessary to resort to recursive locking.
.Pp
Non-MPSAFE file systems exist, requiring callers to conditionally unlock
.Va Giant .