diff options
Diffstat (limited to 'sbin/mount_null/mount_null.8')
| -rw-r--r-- | sbin/mount_null/mount_null.8 | 42 |
1 files changed, 23 insertions, 19 deletions
diff --git a/sbin/mount_null/mount_null.8 b/sbin/mount_null/mount_null.8 index 0eee27d0b5b..f7f3a3afa93 100644 --- a/sbin/mount_null/mount_null.8 +++ b/sbin/mount_null/mount_null.8 @@ -1,4 +1,4 @@ -.\" $OpenBSD: mount_null.8,v 1.13 1999/09/23 04:12:02 alex Exp $ +.\" $OpenBSD: mount_null.8,v 1.14 2000/03/18 22:56:00 aaron Exp $ .\" $NetBSD: mount_null.8,v 1.4 1996/04/10 20:57:19 thorpej Exp $ .\" .\" Copyright (c) 1992, 1993, 1994 @@ -90,23 +90,26 @@ New null layers are created with .Nm takes two arguments: the pathname of the lower vfs (target-pn) and the pathname where the null -layer will appear in the namespace (mount-point-pn). After -the null layer is put into place, the contents +layer will appear in the namespace (mount-point-pn). +After the null layer is put into place, the contents of target-pn subtree will be aliased under mount-point-pn. .\" .\" .Sh OPERATION OF A NULL LAYER The null layer is the minimum file system layer, simply bypassing all possible operations to the lower layer -for processing there. The majority of its activity centers +for processing there. +The majority of its activity centers on the bypass routine, through which nearly all vnode operations pass. .Pp The bypass routine accepts arbitrary vnode operations for -handling by the lower layer. It begins by examining vnode +handling by the lower layer. +It begins by examining vnode operation arguments and replacing any null-nodes by their -lower-layer equivalents. It then invokes the operation -on the lower layer. Finally, it replaces the null-nodes +lower-layer equivalents. +It then invokes the operation on the lower layer. +Finally, it replaces the null-nodes in the arguments and, if a vnode is returned by the operation, stacks a null-node on top of the returned vnode. .Pp @@ -131,12 +134,12 @@ information. .\" .Sh INSTANTIATING VNODE STACKS Mounting associates the null layer with a lower layer, -in effect stacking two VFSes. Vnode stacks are instead -created on demand as files are accessed. +in effect stacking two VFSes. +Vnode stacks are instead created on demand as files are accessed. .Pp The initial mount creates a single vnode stack for the -root of the new null layer. All other vnode stacks -are created as a result of vnode operations on +root of the new null layer. +All other vnode stacks are created as a result of vnode operations on this or other null vnode stacks. .Pp New vnode stacks come into existence as a result of @@ -158,7 +161,8 @@ Now consider opening A .Em vop_lookup would be -done on the root null-node. This operation would bypass through +done on the root null-node. +This operation would bypass through to the lower layer which would return a vnode representing the UFS .Pa sys . @@ -186,16 +190,16 @@ null layer. .\" .Sh INVOKING OPERATIONS ON LOWER LAYERS There are two techniques to invoke operations on a lower layer -when the operation cannot be completely bypassed. Each method -is appropriate in different situations. In both cases, -it is the responsibility of the aliasing layer to make +when the operation cannot be completely bypassed. +Each method is appropriate in different situations. +In both cases, it is the responsibility of the aliasing layer to make the operation arguments "correct" for the lower layer by mapping an vnode arguments to the lower layer. .Pp The first approach is to call the aliasing layer's bypass routine. This method is most suitable when you wish to invoke the operation -currently being handled on the lower layer. It has the advantage -the bypass routine already must do argument mapping. +currently being handled on the lower layer. +It has the advantage the bypass routine already must do argument mapping. An example of this is .Em null_getattrs in the null layer. @@ -205,8 +209,8 @@ the lower layer with the .Em VOP_OPERATIONNAME interface. The advantage of this method is that it is easy to invoke -arbitrary operations on the lower layer. The disadvantage -is that vnodes arguments must be manually mapped. +arbitrary operations on the lower layer. +The disadvantage is that vnodes arguments must be manually mapped. .\" .\" .Sh SEE ALSO |