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Diffstat (limited to 'share/man/man9/vnode.9')
| -rw-r--r-- | share/man/man9/vnode.9 | 62 |
1 files changed, 32 insertions, 30 deletions
diff --git a/share/man/man9/vnode.9 b/share/man/man9/vnode.9 index 1f7c604d750..75c6c3775f4 100644 --- a/share/man/man9/vnode.9 +++ b/share/man/man9/vnode.9 @@ -1,4 +1,4 @@ -.\" $OpenBSD: vnode.9,v 1.16 2003/04/02 19:00:26 jmc Exp $ +.\" $OpenBSD: vnode.9,v 1.17 2003/04/20 20:46:14 jmc Exp $ .\" .\" Copyright (c) 2001 Constantine Sapuntzakis .\" All rights reserved. @@ -39,7 +39,7 @@ Each vnode has a set of methods which start with string 'VOP_'. These methods include VOP_OPEN, VOP_READ, VOP_WRITE, VOP_RENAME, VOP_CLOSE, VOP_MKDIR. Many of these methods correspond closely to the equivalent -file system call--open, read, write, rename, etc. +file system call - open, read, write, rename, etc. Each file system (FFS, NFS, etc.) provides implementations for these methods. .Pp The Virtual File System (VFS) library maintains a pool of vnodes. @@ -62,13 +62,15 @@ is called "active". When a vnode's reference count drops to zero, it becomes "inactive", that is, a candidate for reuse. An "inactive" vnode still refers to a valid file and one can try to -reactivate it using vget (this is used a lot by caches). +reactivate it using +.Xr vget 9 +(this is used a lot by caches). .Pp Before the VFS can reuse an inactive vnode to refer to another file, it must clean all information pertaining to the old file. A cleaned out vnode is called a "reclaimed" vnode. .Pp -To support forceable unmounts and the +To support forceable unmounts and the .Xr revoke 2 system call, the VFS may "reclaim" a vnode with a positive reference count. @@ -78,20 +80,20 @@ The reclaimed vnode will not be re-used for another file until its reference count hits zero. .Ss Vnode pool The -.Xr getnewvnode 9 -system call allocates a vnode from the pool, possible reusing an +.Xr getnewvnode 9 +system call allocates a vnode from the pool, possibly reusing an "inactive" vnode, and returns it to the caller. The vnode returned has a reference count (v_usecount) of 1. .Pp -The -.Xr vref 9 +The +.Xr vref 9 call increments the reference count on the vnode. It may only be on a vnode with reference count of 1 or greater. The .Xr vrele 9 -and -.Xr vput 9 -calls decrement the reference count. +and +.Xr vput 9 +calls decrement the reference count. In addition, the .Xr vput 9 call also releases the vnode lock. @@ -105,18 +107,18 @@ However, if the vnode is being reclaimed concurrently, then vget will fail and return an error. .Pp The -.Xr vgone 9 -and -.Xr vgonel 9 +.Xr vgone 9 +and +.Xr vgonel 9 orchestrate the reclamation of a vnode. They can be called on both active and inactive vnodes. .Pp When transitioning a vnode to the "reclaimed" state, the VFS will call -.Xr VOP_RECLAIM 9 +.Xr VOP_RECLAIM 9 method. File systems use this method to free any file-system specific data they attached to the vnode. -.Ss Vnode locks +.Ss Vnode locks The vnode actually has three different types of lock: the vnode lock, the vnode interlock, and the vnode reclamation lock (VXLOCK). .Ss The vnode lock @@ -139,7 +141,7 @@ Otherwise, the file system's behavior is undefined. On rare occasions, code will hold the vnode lock so that a series of VOP_ operations occurs as an atomic unit. (Of course, this doesn't work with network file systems like NFSv2 that don't -have any notion of bundling a bunch of operations into an atomic unit) +have any notion of bundling a bunch of operations into an atomic unit.) .It While the vnode lock is held, the vnode will not be reclaimed. .El @@ -147,11 +149,11 @@ While the vnode lock is held, the vnode will not be reclaimed. There is a discipline to using the vnode lock. Some VOP_ operations require that the vnode lock is held before being called. A description of this rather arcane locking discipline is in -sys/kern/vnode_if.src. +.Pa sys/kern/vnode_if.src . .Pp -The vnode lock is acquired by calling -.Xr vn_lock 9 -and released by calling +The vnode lock is acquired by calling +.Xr vn_lock 9 +and released by calling .Xr VOP_UNLOCK 9 . .Pp A process is allowed to sleep while holding the vnode lock. @@ -174,18 +176,18 @@ Operations on this lock are a no-op on uniprocessor systems. The vnode reclamation lock (VXLOCK) is used to prevent multiple processes from entering the vnode reclamation code. It is also used as a flag to indicate that reclamation is in progress. -The VXWANT flag is set by processes that wish to woken up when reclamation +The VXWANT flag is set by processes that wish to be woken up when reclamation is finished. .Pp -The +The .Xr vwaitforio 9 -call is used for to wait for all outstanding write I/Os associated with a -vnode to complete. +call is used to wait for all outstanding write I/Os associated with a +vnode to complete. .Ss Version number/capability The vnode capability, v_id, is a 32-bit version number on the vnode. Every time a vnode is reassigned to a new file, the vnode capability is changed. -This is used by code that wish to keep pointers to vnodes but doesn't want +This is used by code that wishes to keep pointers to vnodes but doesn't want to hold a reference (e.g., caches). The code keeps both a vnode * and a copy of the capability. The code can later compare the vnode's capability to its copy and see @@ -212,12 +214,12 @@ The v_tag attribute is read-only. .Pp The v_type attribute indicates what type of file (e.g. directory, regular, FIFO) this vnode is. -This is used by the generic code to ensure for various checks. +This is used by the generic code for various checks. For example, the -.Xr read 2 +.Xr read 2 system call returns an error when a read is attempted on a directory. .Pp -The v_data attribute allows a file system to attach piece of file +The v_data attribute allows a file system to attach a piece of file system specific memory to the vnode. This contains information about the file that is specific to the file system. @@ -238,7 +240,7 @@ The exceptions are bgetvp and brelvp. The following fields of the vnode are manipulated at interrupt level: v_numoutput, v_holdcnt, v_dirtyblkhd, v_cleanblkhd, v_bioflag, v_freelist, and v_synclist. -Any accesses to these fields should be protected by splbio. +Any access to these fields should be protected by splbio. .Sh HISTORY This document first appeared in .Ox 2.9 . |