NAME [Toc]

 vnode -- internal representation of a file or directory

SYNOPSIS [Toc]

 #include <sys/param.h>
 #include <sys/vnode.h>

DESCRIPTION [Toc]

 The vnode is the focus of all file activity in UNIX. A 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 three reference counts, v_usecount, v_holdcnt and
 v_writecount. The first is the number of clients within the kernel which
 are using this vnode. This count is maintained by vref(9), vrele(9) and
 vput(9). The second is the number of clients within the kernel who veto
 the recycling of this vnode. This count is maintained by vhold(9) and
 vdrop(9).	When both the v_usecount and the v_holdcnt of a vnode reaches
 zero then the vnode will be put on the freelist and may be reused for
 another file, possibly in another file system. The transition to and
 from the freelist is handled by getnewvnode(9), vfree(9) and vbusy(9).
 The third is a count of the number of clients which are writing into the
 file. It is maintained by the open(2) and close(2) system calls.
 Any call which returns a vnode (e.g. vget(9), VOP_LOOKUP(9) etc.)	will
 increase the v_usecount of the vnode by one. When the caller is finished
 with the vnode, it should release this reference by calling vrele(9) (or
 vput(9) if the vnode is locked).
 Other commonly used members of the vnode structure are v_id which is used
 to maintain consistency in the name cache, v_mount which points at the
 file system which owns the vnode, v_type which contains the type of
 object the vnode represents and v_data which is used by file systems to
 store file system specific data with the vnode. The v_op field is used
 by the VOP_* macros to call functions in the file system which implement
 the vnode's functionality.

VNODE TYPES [Toc]

 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 [Toc]

 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.
 Calls to malloc(9) or free(9) when holding a vnode interlock, will cause
 a LOR (Lock Order Reversal) due to the intertwining of VM Objects and
 Vnodes.

SEE ALSO [Toc]

 malloc(9), VFS(9)

AUTHORS [Toc]

 This man page was written by Doug Rabson.
FreeBSD 5.2.1			 May 20, 2003			 FreeBSD 5.2.1