168 lines
4.5 KiB
Groff
168 lines
4.5 KiB
Groff
.\" 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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.\" $FreeBSD$
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.\"
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.Dd May 20, 2003
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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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.In sys/param.h
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.In sys/vnode.h
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.Sh DESCRIPTION
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The vnode is the focus of all file activity in
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.Ux .
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A vnode is described by
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.Vt "struct vnode" .
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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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.Va v_usecount ,
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.Va v_holdcnt
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and
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.Va 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.
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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.
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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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.Va v_usecount
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and the
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.Va 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 file system.
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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.
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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 vget 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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.Va v_usecount
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of the vnode by one.
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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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.Va v_id
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which is used to maintain consistency in the name cache,
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.Va v_mount
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which points at the file system which owns the vnode,
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.Va v_type
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which contains the type of object the vnode represents and
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.Va v_data
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which is used by file systems to store file system specific data with
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the vnode.
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The
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.Va 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 file system 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.
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If you want 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.
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If you want 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.
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Advisory locking will not work on this.
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.It Dv VFIFO
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A FIFO (named pipe).
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Advisory locking will not 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 IMPLEMENTATION 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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.Pp
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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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.Pp
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Calls to
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.Xr malloc 9
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or
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.Xr free 9
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when holding a
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.Nm
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interlock, will cause a LOR (Lock Order Reversal) due to the
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intertwining of VM Objects and Vnodes.
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.Sh SEE ALSO
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.Xr malloc 9 ,
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.Xr VFS 9
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.Sh AUTHORS
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This manual page was written by
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.An Doug Rabson .
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