NAME
vnode —
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. Thevnode 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 allocation 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. Auxiliary 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 managed 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 discrete open() calls made
on the vnode for the purpose of writing. This field will be a subset of
v_opencount. These fields are managed primarily by
calls to
vn_open(9) and
vn_close(9).
A deactivated vnode or a vnode in an unknown state accessed from an Auxiliary 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
filesystems 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 ALSO
AUTHORS
This manual page was written by Doug Rabson.