VNODE(9) BSD Kernel Developer's Manual VNODE(9)NAMEvnode — internal representation of a file, directory, or other VFS entity
SYNOPSIS
#include <sys/param.h>
#include <sys/vnode.h>
DESCRIPTION
The vnode is the focus of all file activity in UNIX. The vnode is
described by struct vnode. There is a unique vnode allocated for each
active file, each current directory, each mounted-on file, text file, and
the root.
Each vnode has numerous reference counts, v_sysref, v_auxrefs,
v_opencount, and v_writecount.
v_sysref represents the number of primary references to the vnode. It is
actually a structure which utilizes the SYSREF API and also manages allo‐
cation and deallocation of the vnode. Primary references keep a vnode
ready for I/O and prevent it from being deactivated. Primary references
are managed by vref(9) and vrele(9).
v_auxrefs represents the number of auxiliary references to a vnode. Aux‐
iliary references prevent a vnode from being reclaimed (if not already
being reclaimed), reused for other purposes, or otherwise destroyed, but
do not activate or deactivate the vnode. Auxiliary references are man‐
aged by vhold(9) and vdrop(9).
v_opencount represents the number of discrete open() calls made on the
vnode (reading or writing). v_writecount represents the number of dis‐
crete open() calls made on the vnode for the purpose of writing. This
field will be a subset of v_opencount. These fields are managed primar‐
ily by calls to vn_open(9) and vn_close(9).
A deactivated vnode or a vnode in an unknown state accessed from an Aux‐
iliary data structure can be reactivated, referenced, and locked using
vget(9) and vput(9).
An actively referenced and possibly locked vnode must be passed to most
kernel procedures taking a vnode as an argument. Most kernel procedures
returning a vnode will return one that is actively referenced.
Other commonly used members of the vnode structure are v_mount which
points at the filesystem which owns the vnode, v_type which contains the
type of object the vnode represents and v_data which is used by filesys‐
tems to store filesystem specific data with the vnode. The v_ops field
is used by the VOP_* macros to call functions in the filesystem which
implement the vnode's functionality.
VNODE TYPES
VNON No type.
VREG A regular file; may be with or without VM object backing. If you
want to make sure this get a backing object, call
vfs_object_create(9).
VDIR A directory.
VBLK A block device; may be with or without VM object backing. If you
want to make sure this get a backing object, call
vfs_object_create(9).
VCHR A character device.
VLNK A symbolic link.
VSOCK A socket. Advisory locking won't work on this.
VFIFO A FIFO (named pipe). Advisory locking won't work on this.
VBAD An old style bad sector map.
IMPLEMENTATION NOTES
VFIFO uses the struct fileops from /sys/kern/sys_pipe.c. VSOCK uses the
struct fileops from /sys/kern/sys_socket.c. Everything else uses the one
from /sys/kern/vfs_vnops.c.
The VFIFO/VSOCK code, which is why struct fileops is used at all, is an
artifact of an incomplete integration of the VFS code into the kernel.
SEE ALSOVFS(9)AUTHORS
This manual page was written by Doug Rabson.
BSD May 5, 2007 BSD
