238 lines
7.7 KiB
Groff
238 lines
7.7 KiB
Groff
.\" -*- nroff -*-
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.\"
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.\" Copyright (c) 1996 Doug Rabson
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.\"
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.\" All rights reserved.
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.\"
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.\" This program is free software.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $Id: vnode.9,v 1.6 1998/03/12 07:31:20 charnier Exp $
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.\"
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.Dd July 24, 1996
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.Os
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.Dt VNODE 9
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.Sh NAME
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.Nm vnode
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.Nd internal representation of a file or directory
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.Sh SYNOPSIS
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.Fd #include <sys/param.h>
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.Fd #include <sys/vnode.h>
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.Pp
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.Bd -literal
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/*
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* Vnode types. VNON means no type.
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*/
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enum vtype { VNON, VREG, VDIR, VBLK, VCHR, VLNK, VSOCK, VFIFO, VBAD };
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/*
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* Vnode tag types.
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* These are for the benefit of external programs only (e.g., pstat)
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* and should NEVER be inspected by the kernel.
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*/
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enum vtagtype {
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VT_NON, VT_UFS, VT_NFS, VT_MFS, VT_PC, VT_LFS, VT_LOFS, VT_FDESC,
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VT_PORTAL, VT_NULL, VT_UMAP, VT_KERNFS, VT_PROCFS, VT_AFS, VT_ISOFS,
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VT_UNION, VT_MSDOSFS, VT_DEVFS
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};
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/*
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* Each underlying filesystem allocates its own private area and hangs
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* it from v_data. If non-null, this area is freed in getnewvnode().
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*/
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LIST_HEAD(buflists, buf);
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typedef int vop_t __P((void *));
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struct vnode {
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u_long v_flag; /* vnode flags (see below) */
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int v_usecount; /* reference count of users */
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int v_writecount; /* reference count of writers */
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int v_holdcnt; /* page & buffer references */
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daddr_t v_lastr; /* last read (read-ahead) */
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u_long v_id; /* capability identifier */
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struct mount *v_mount; /* ptr to vfs we are in */
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vop_t **v_op; /* vnode operations vector */
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TAILQ_ENTRY(vnode) v_freelist; /* vnode freelist */
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LIST_ENTRY(vnode) v_mntvnodes; /* vnodes for mount point */
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struct buflists v_cleanblkhd; /* clean blocklist head */
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struct buflists v_dirtyblkhd; /* dirty blocklist head */
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long v_numoutput; /* num of writes in progress */
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enum vtype v_type; /* vnode type */
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union {
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struct mount *vu_mountedhere;/* ptr to mounted vfs (VDIR) */
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struct socket *vu_socket; /* unix ipc (VSOCK) */
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struct specinfo *vu_specinfo; /* device (VCHR, VBLK) */
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struct fifoinfo *vu_fifoinfo; /* fifo (VFIFO) */
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} v_un;
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struct nqlease *v_lease; /* Soft reference to lease */
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daddr_t v_lastw; /* last write (write cluster) */
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daddr_t v_cstart; /* start block of cluster */
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daddr_t v_lasta; /* last allocation */
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int v_clen; /* length of current cluster */
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int v_ralen; /* Read-ahead length */
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int v_usage; /* Vnode usage counter */
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daddr_t v_maxra; /* last readahead block */
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void *v_object; /* Place to store VM object */
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enum vtagtype v_tag; /* type of underlying data */
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void *v_data; /* private data for fs */
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};
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#define v_mountedhere v_un.vu_mountedhere
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#define v_socket v_un.vu_socket
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#define v_specinfo v_un.vu_specinfo
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#define v_fifoinfo v_un.vu_fifoinfo
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/*
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* Vnode flags.
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*/
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#define VROOT 0x00001 /* root of its file system */
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#define VTEXT 0x00002 /* vnode is a pure text prototype */
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#define VSYSTEM 0x00004 /* vnode being used by kernel */
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#define VOLOCK 0x00008 /* vnode is locked waiting for an object */
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#define VOWANT 0x00010 /* a process is waiting for VOLOCK */
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#define VXLOCK 0x00100 /* vnode is locked to change underlying type */
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#define VXWANT 0x00200 /* process is waiting for vnode */
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#define VBWAIT 0x00400 /* waiting for output to complete */
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#define VALIASED 0x00800 /* vnode has an alias */
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#define VDIROP 0x01000 /* LFS: vnode is involved in a directory op */
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#define VVMIO 0x02000 /* VMIO flag */
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#define VNINACT 0x04000 /* LFS: skip ufs_inactive() in lfs_vunref */
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#define VAGE 0x08000 /* Insert vnode at head of free list */
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#define VOLOCK 0x10000 /* vnode is locked waiting for an object */
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#define VOWANT 0x20000 /* a process is waiting for VOLOCK */
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#define VDOOMED 0x40000 /* This vnode is being recycled */
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#define VFREE 0x80000 /* This vnode is on the freelist */
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.Ed
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.Sh DESCRIPTION
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The vnode is the focus of all file activity in UNIX. There is a
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unique vnode allocated for each active file, each current directory,
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each mounted-on file, text file, and the root.
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.Pp
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Each vnode has three reference counts,
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.Dv v_usecount ,
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.Dv v_holdcnt
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and
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.Dv v_writecount .
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The first is the number of clients within the kernel which are
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using this vnode. This count is maintained by
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.Xr vref 9 ,
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.Xr vrele 9
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and
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.Xr vput 9 .
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The second is the number of clients within the kernel who veto
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the recycling of this vnode. This count is
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maintained by
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.Xr vhold 9
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and
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.Xr vdrop 9 .
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When both the
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.Dv v_usecount
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and the
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.Dv v_holdcnt
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of a vnode reaches zero then the vnode will be put on the freelist
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and may be reused for another file, possibly in another filesystem.
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The transition to and from the freelist is handled by
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.Xr getnewvnode 9 ,
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.Xr vfree 9
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and
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.Xr vbusy 9 .
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The third is a count of the number of clients which are writing into
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the file. It is maintained by the
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.Xr open 2
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and
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.Xr close 2
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system calls.
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.Pp
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Any call which returns a vnode (e.g.
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.Xr VFS_GET 9 ,
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.Xr VOP_LOOKUP 9
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etc.)
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will increase the
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.Dv v_usecount
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of the vnode by one. When the caller is finished with the vnode, it
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should release this reference by calling
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.Xr vrele 9
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(or
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.Xr vput 9
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if the vnode is locked).
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.Pp
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Other commonly used members of the vnode structure are
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.Dv v_id
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which is used to maintain consistency in the name cache,
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.Dv v_mount
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which points at the filesystem which owns the vnode,
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.Dv v_type
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which contains the type of object the vnode represents and
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.Dv v_data
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which is used by filesystems to store filesystem specific data with
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the vnode.
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The
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.Dv v_op
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field is used by the
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.Dv VOP_*
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macros to call functions in the filesystem which implement the vnode's
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functionality.
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.Sh VNODE TYPES
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.Bl -tag -width VSOCK
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.It Dv VNON
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No type.
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.It Dv VREG
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A regular file; may be with or without VM object backing. If you want
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to make sure this get a backing object, call
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.Xr vfs_object_create 9 .
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.It Dv VDIR
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A directory.
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.It Dv VBLK
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A block device; may be with or without VM object backing. If you want
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to make sure this get a backing object, call
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.Xr vfs_object_create 9 .
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.It Dv VCHR
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A character device.
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.It Dv VLNK
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A symbolic link.
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.It Dv VSOCK
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A socket. Advisory locking won't work on this.
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.It Dv VFIFO
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A FIFO (named pipe). Adviseroty locking won't work on this.
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.It Dv VBAD
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An old style bad sector map
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.El
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.Sh NOTES
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VFIFO uses the "struct fileops" from
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.Pa /sys/kern/sys_pipe.c .
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VSOCK uses the "struct fileops" from
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.Pa /sys/kern/sys_socket.c .
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Everything else uses the one from
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.Pa /sys/kern/vfs_vnops.c .
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The VFIFO/VSOCK code, which is why "struct fileops" is used at all, is
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an artifact of an incomplete integration of the VFS code into the
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kernel.
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.Sh SEE ALSO
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.Xr VFS 9
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.Sh AUTHORS
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This man page was written by
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.An Doug Rabson .
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