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vtryget: try to get an initial reference to a vnode without taking its 

interlock. Only works if v_usecount is already non-zero, which is nearly
always true for busy files like libc.so or ld_elf.so.
This commit is contained in:
ad 2008-06-03 14:54:12 +00:00
parent e437f08c73
commit 457a3f8942
2 changed files with 34 additions and 3 deletions
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34
sys/kern/vfs_subr.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: vfs_subr.c,v 1.348 2008/06/02 22:56:09 ad Exp $ */
/* $NetBSD: vfs_subr.c,v 1.349 2008/06/03 14:54:12 ad Exp $ */
/*-
* Copyright (c) 1997, 1998, 2004, 2005, 2007, 2008 The NetBSD Foundation, Inc.
@ -87,7 +87,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: vfs_subr.c,v 1.348 2008/06/02 22:56:09 ad Exp $");
__KERNEL_RCSID(0, "$NetBSD: vfs_subr.c,v 1.349 2008/06/03 14:54:12 ad Exp $");
#include "opt_ddb.h"
#include "opt_compat_netbsd.h"
@ -712,6 +712,36 @@ getdevvp(dev_t dev, vnode_t **vpp, enum vtype type)
return (0);
}
/*
* Try to gain a reference to a vnode, without acquiring its interlock.
* The caller must hold a lock that will prevent the vnode from being
* recycled or freed.
*/
bool
vtryget(vnode_t *vp)
{
u_int use, next;
/*
* If the vnode is being freed, don't make life any harder
* for vclean() by adding another reference without waiting.
* This is not strictly necessary, but we'll do it anyway.
*/
if (__predict_false((vp->v_iflag & (VI_XLOCK | VI_FREEING)) != 0)) {
return false;
}
for (use = vp->v_usecount;; use = next) {
if (use == 0) {
/* Need interlock held if first reference. */
return false;
}
next = atomic_cas_uint(&vp->v_usecount, use, use + 1);
if (__predict_true(next == use)) {
return true;
}
}
}
/*
* Grab a particular vnode from the free list, increment its
* reference count and lock it. If the vnode lock bit is set the

3
sys/sys/vnode.h
View File

@ -1,4 +1,4 @@
/* $NetBSD: vnode.h,v 1.194 2008/06/02 16:25:34 ad Exp $ */
/* $NetBSD: vnode.h,v 1.195 2008/06/03 14:54:12 ad Exp $ */
/*-
* Copyright (c) 2008 The NetBSD Foundation, Inc.
@ -595,6 +595,7 @@ int vfinddev(dev_t, enum vtype, struct vnode **);
int vflush(struct mount *, struct vnode *, int);
void vflushbuf(struct vnode *, int);
int vget(struct vnode *, int);
bool vtryget(struct vnode *);
void vgone(struct vnode *);
void vgonel(struct vnode *, struct lwp *);
int vinvalbuf(struct vnode *, int, kauth_cred_t, struct lwp *, bool, int);