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VNODE(9)	       FreeBSD 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
     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
     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	will not work on this.

     VFIFO  A FIFO (named pipe).  Advisory locking will	not work on this.

     VBAD   Indicates that the vnode has been reclaimed.

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
     Vnodes.

SEE ALSO
     malloc(9),	VOP_ACCESS(9), VOP_ACLCHECK(9),	VOP_ADVLOCK(9),	VOP_ATTRIB(9),
     VOP_BWRITE(9), VOP_CREATE(9), VOP_FSYNC(9), VOP_GETACL(9),
     VOP_GETEXTATTR(9),	VOP_GETPAGES(9), VOP_GETVOBJECT(9), VOP_INACTIVE(9),
     VOP_IOCTL(9), VOP_LINK(9),	VOP_LISTEXTATTR(9), VOP_LOCK(9),
     VOP_LOOKUP(9), VOP_OPENCLOSE(9), VOP_PATHCONF(9), VOP_PRINT(9),
     VOP_RDWR(9), VOP_READDIR(9), VOP_READLINK(9), VOP_REALLOCBLKS(9),
     VOP_REMOVE(9), VOP_RENAME(9), VOP_REVOKE(9), VOP_SETACL(9),
     VOP_SETEXTATTR(9),	VOP_STRATEGY(9), VOP_VPTOCNP(9), VOP_VPTOFH(9),	VFS(9)

AUTHORS
     This manual page was written by Doug Rabson.

FreeBSD	10.1		       February	13, 2010		  FreeBSD 10.1

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

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