HardenedBSD/share/man/man9/vnode.9

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.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.