Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
VNODE(9)		 BSD Kernel Developer's	Manual		      VNODE(9)

NAME
     vnode -- internal representation of a file	or directory

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

DESCRIPTION
     The vnode is the focus of all file	activity in UNIX.  A vnode is de-
     scribed by	struct vnode.  There is	a unique vnode allocated for each ac-
     tive 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 an-
     other 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. VFS_GET(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 ob-
     ject 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
     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.

     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 Vn-
     odes.

SEE ALSO
     malloc(9),	VFS(9)

AUTHORS
     This man page was written by Doug Rabson.

BSD				 May 20, 2003				   BSD

NAME | SYNOPSIS | DESCRIPTION | VNODE TYPES | IMPLEMENTATION NOTES | SEE ALSO | AUTHORS

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=vnode&sektion=9&manpath=FreeBSD+5.1-RELEASE>

home | help