Module Name: src
Committed By: rmind
Date: Thu May 19 03:26:06 UTC 2011
Modified Files:
src/sys/kern: vfs_vnode.c
Log Message:
Add some general description of vnode life-cycle.
To generate a diff of this commit:
cvs rdiff -u -r1.7 -r1.8 src/sys/kern/vfs_vnode.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/vfs_vnode.c
diff -u src/sys/kern/vfs_vnode.c:1.7 src/sys/kern/vfs_vnode.c:1.8
--- src/sys/kern/vfs_vnode.c:1.7 Thu May 19 03:11:55 2011
+++ src/sys/kern/vfs_vnode.c Thu May 19 03:26:06 2011
@@ -1,4 +1,4 @@
-/* $NetBSD: vfs_vnode.c,v 1.7 2011/05/19 03:11:55 rmind Exp $ */
+/* $NetBSD: vfs_vnode.c,v 1.8 2011/05/19 03:26:06 rmind Exp $ */
/*-
* Copyright (c) 1997-2011 The NetBSD Foundation, Inc.
@@ -67,31 +67,61 @@
*/
/*
- * Note on v_usecount and locking:
+ * The vnode cache subsystem.
*
- * At nearly all points it is known that v_usecount could be zero, the
- * vnode interlock will be held.
+ * Life-cycle
*
- * To change v_usecount away from zero, the interlock must be held. To
- * change from a non-zero value to zero, again the interlock must be
- * held.
- *
- * There's a flag bit, VC_XLOCK, embedded in v_usecount.
- * To raise v_usecount, if the VC_XLOCK bit is set in it, the interlock
- * must be held.
- * To modify the VC_XLOCK bit, the interlock must be held.
- * We always keep the usecount (v_usecount & VC_MASK) non-zero while the
- * VC_XLOCK bit is set.
- *
- * Unless the VC_XLOCK bit is set, changing the usecount from a non-zero
- * value to a non-zero value can safely be done using atomic operations,
- * without the interlock held.
- * Even if the VC_XLOCK bit is set, decreasing the usecount to a non-zero
- * value can be done using atomic operations, without the interlock held.
+ * Normally, there are two points where new vnodes are created:
+ * VOP_CREATE(9) and VOP_LOOKUP(9). The life-cycle of a vnode
+ * starts in one of the following ways:
+ *
+ * - Allocation, via getnewvnode(9) and/or vnalloc(9).
+ * - Recycle from a free list, via getnewvnode(9) -> getcleanvnode(9).
+ * - Reclamation of inactive vnode, via vget(9).
+ *
+ * The life-cycle ends when the last reference is dropped, usually
+ * in VOP_REMOVE(9). In such case, VOP_INACTIVE(9) is called to inform
+ * the file system that vnode is inactive. Via this call, file system
+ * indicates whether vnode should be recycled (usually, count of links
+ * is checked i.e. whether file was removed).
+ *
+ * Depending on indication, vnode can be put into a free list (cache),
+ * or cleaned via vclean(9), which calls VOP_RECLAIM(9) to disassociate
+ * underlying file system from the vnode, and finally destroyed.
+ *
+ * Reference counting
+ *
+ * Vnode is considered active, if reference count (vnode_t::v_usecount)
+ * is non-zero. It is maintained using: vref(9) and vrele(9), as well
+ * as vput(9), routines. Common points holding references are e.g.
+ * file openings, current working directory, mount points, etc.
+ *
+ * Note on v_usecount and its locking
+ *
+ * At nearly all points it is known that v_usecount could be zero,
+ * the vnode_t::v_interlock will be held. To change v_usecount away
+ * from zero, the interlock must be held. To change from a non-zero
+ * value to zero, again the interlock must be held.
+ *
+ * There is a flag bit, VC_XLOCK, embedded in v_usecount. To raise
+ * v_usecount, if the VC_XLOCK bit is set in it, the interlock must
+ * be held. To modify the VC_XLOCK bit, the interlock must be held.
+ * We always keep the usecount (v_usecount & VC_MASK) non-zero while
+ * the VC_XLOCK bit is set.
+ *
+ * Unless the VC_XLOCK bit is set, changing the usecount from a non-zero
+ * value to a non-zero value can safely be done using atomic operations,
+ * without the interlock held.
+ *
+ * Even if the VC_XLOCK bit is set, decreasing the usecount to a non-zero
+ * value can be done using atomic operations, without the interlock held.
+ *
+ * Note: if VI_CLEAN is set, vnode_t::v_interlock will be released while
+ * mntvnode_lock is still held.
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.7 2011/05/19 03:11:55 rmind Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.8 2011/05/19 03:26:06 rmind Exp $");
#include <sys/param.h>
#include <sys/kernel.h>
