freebsd-nq/share/man/man9/vnode.9
1998-02-28 15:37:25 +00:00

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.\" -*- nroff -*-
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.\" Copyright (c) 1996 Doug Rabson
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.\" $Id: vnode.9,v 1.4 1997/10/11 07:39:45 phk Exp $
.\"
.Dd July 24, 1996
.Os
.Dt VNODE 9
.Sh NAME
.Nm vnode
.Nd internal representation of a file or directory
.Sh SYNOPSIS
.Fd #include <sys/param.h>
.Fd #include <sys/vnode.h>
.Pp
.Bd -literal
/*
* Vnode types. VNON means no type.
*/
enum vtype { VNON, VREG, VDIR, VBLK, VCHR, VLNK, VSOCK, VFIFO, VBAD };
/*
* Vnode tag types.
* These are for the benefit of external programs only (e.g., pstat)
* and should NEVER be inspected by the kernel.
*/
enum vtagtype {
VT_NON, VT_UFS, VT_NFS, VT_MFS, VT_PC, VT_LFS, VT_LOFS, VT_FDESC,
VT_PORTAL, VT_NULL, VT_UMAP, VT_KERNFS, VT_PROCFS, VT_AFS, VT_ISOFS,
VT_UNION, VT_MSDOSFS, VT_DEVFS
};
/*
* Each underlying filesystem allocates its own private area and hangs
* it from v_data. If non-null, this area is freed in getnewvnode().
*/
LIST_HEAD(buflists, buf);
typedef int vop_t __P((void *));
struct vnode {
u_long v_flag; /* vnode flags (see below) */
int v_usecount; /* reference count of users */
int v_writecount; /* reference count of writers */
int v_holdcnt; /* page & buffer references */
daddr_t v_lastr; /* last read (read-ahead) */
u_long v_id; /* capability identifier */
struct mount *v_mount; /* ptr to vfs we are in */
vop_t **v_op; /* vnode operations vector */
TAILQ_ENTRY(vnode) v_freelist; /* vnode freelist */
LIST_ENTRY(vnode) v_mntvnodes; /* vnodes for mount point */
struct buflists v_cleanblkhd; /* clean blocklist head */
struct buflists v_dirtyblkhd; /* dirty blocklist head */
long v_numoutput; /* num of writes in progress */
enum vtype v_type; /* vnode type */
union {
struct mount *vu_mountedhere;/* ptr to mounted vfs (VDIR) */
struct socket *vu_socket; /* unix ipc (VSOCK) */
struct specinfo *vu_specinfo; /* device (VCHR, VBLK) */
struct fifoinfo *vu_fifoinfo; /* fifo (VFIFO) */
} v_un;
struct nqlease *v_lease; /* Soft reference to lease */
daddr_t v_lastw; /* last write (write cluster) */
daddr_t v_cstart; /* start block of cluster */
daddr_t v_lasta; /* last allocation */
int v_clen; /* length of current cluster */
int v_ralen; /* Read-ahead length */
int v_usage; /* Vnode usage counter */
daddr_t v_maxra; /* last readahead block */
void *v_object; /* Place to store VM object */
enum vtagtype v_tag; /* type of underlying data */
void *v_data; /* private data for fs */
};
#define v_mountedhere v_un.vu_mountedhere
#define v_socket v_un.vu_socket
#define v_specinfo v_un.vu_specinfo
#define v_fifoinfo v_un.vu_fifoinfo
/*
* Vnode flags.
*/
#define VROOT 0x00001 /* root of its file system */
#define VTEXT 0x00002 /* vnode is a pure text prototype */
#define VSYSTEM 0x00004 /* vnode being used by kernel */
#define VOLOCK 0x00008 /* vnode is locked waiting for an object */
#define VOWANT 0x00010 /* a process is waiting for VOLOCK */
#define VXLOCK 0x00100 /* vnode is locked to change underlying type */
#define VXWANT 0x00200 /* process is waiting for vnode */
#define VBWAIT 0x00400 /* waiting for output to complete */
#define VALIASED 0x00800 /* vnode has an alias */
#define VDIROP 0x01000 /* LFS: vnode is involved in a directory op */
#define VVMIO 0x02000 /* VMIO flag */
#define VNINACT 0x04000 /* LFS: skip ufs_inactive() in lfs_vunref */
#define VAGE 0x08000 /* Insert vnode at head of free list */
#define VOLOCK 0x10000 /* vnode is locked waiting for an object */
#define VOWANT 0x20000 /* a process is waiting for VOLOCK */
#define VDOOMED 0x40000 /* This vnode is being recycled */
#define VFREE 0x80000 /* This vnode is on the freelist */
.Ed
.Sh DESCRIPTION
The vnode is the focus of all file activity in UNIX. There is a
unique vnode allocated for each active file, each current directory,
each mounted-on file, text file, and the root.
.Pp
Each vnode has three reference counts,
.Dv v_usecount ,
.Dv v_holdcnt
and
.Dv v_writecount .
The first is the number of clients within the kernel which are
using this vnode. This count is maintained by
.Xr vref 9 ,
.Xr vrele 9
and
.Xr vput 9 .
The second is the number of clients within the kernel who veto
the recycling of this vnode. This count is
maintained by
.Xr vhold 9
and
.Xr vdrop 9 .
When both the
.Dv v_usecount
and the
.Dv v_holdcnt
of a vnode reaches zero then the vnode will be put on the freelist
and may be reused for another file, possibly in another filesystem.
The transition to and from the freelist is handled by
.Xr getnetvnode 9 ,
.Xr vfree 9
and
.Xr vbusy 9 .
The third is a count of the number of clients which are writing into
the file. It is maintained by the
.Xr open 2
and
.Xr close 2
system calls.
.Pp
Any call which returns a vnode (e.g.
.Xr VFS_GET 9 ,
.Xr VOP_LOOKUP 9
etc.)
will increase the
.Dv v_usecount
of the vnode by one. When the caller is finished with the vnode, it
should release this reference by calling
.Xr vrele 9
(or
.Xr vput 9
if the vnode is locked).
.Pp
Other commonly used members of the vnode structure are
.Dv v_id
which is used to maintain consistency in the name cache,
.Dv v_mount
which points at the filesystem which owns the vnode,
.Dv v_type
which contains the type of object the vnode represents and
.Dv v_data
which is used by filesystems to store filesystem specific data with
the vnode.
The
.Dv v_op
field is used by the
.Dv VOP_*
macros to call functions in the filesystem which implement the vnode's
functionality.
.Sh SEE ALSO
.Xr VFS 9
.Sh AUTHORS
This man page was written by Doug Rabson.