DragonFly On-Line Manual Pages

VNODE(9)              DragonFly Kernel Developer's Manual             VNODE(9)

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.  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 ALSO
     VFS(9)

AUTHORS
     This manual page was written by Doug Rabson.

DragonFly 3.5                     May 5, 2007                    DragonFly 3.5