freebsd-dev/share/man/man9/vnode.9

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.\" Copyright (c) 1996 Doug Rabson
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.\" $Id: vnode.9,v 1.2 1997/03/22 22:47:31 mpp 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 0x0001 /* root of its file system */
#define VTEXT 0x0002 /* vnode is a pure text prototype */
#define VSYSTEM 0x0004 /* vnode being used by kernel */
#define VOLOCK 0x0008 /* vnode is locked waiting for an object */
#define VOWANT 0x0010 /* a process is waiting for VOLOCK */
#define VXLOCK 0x0100 /* vnode is locked to change underlying type */
#define VXWANT 0x0200 /* process is waiting for vnode */
#define VBWAIT 0x0400 /* waiting for output to complete */
#define VALIASED 0x0800 /* vnode has an alias */
#define VDIROP 0x1000 /* LFS: vnode is involved in a directory op */
#define VVMIO 0x2000 /* VMIO flag */
#define VNINACT 0x4000 /* LFS: skip ufs_inactive() in lfs_vunref */
#define VAGE 0x8000 /* Insert vnode at head of free list */
.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 two reference counts,
.Dv v_usecount
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 .
When the
.Dv v_usecount
of a vnode reaches zero then the vnode may be reused for another
file, possibly in another filesystem.
The second 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.