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 from the freelist is handled by getnewvnode(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
vnode_create_vobject(). 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
vnode_create_vobject(). 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), VFS(9), VOP_ACCESS(9), VOP_ACLCHECK(9), VOP_ADVISE(9), VOP_ADVLOCK(9), VOP_ALLOCATE(9), VOP_ATTRIB(9), VOP_BWRITE(9), VOP_CREATE(9), VOP_FSYNC(9), VOP_GETACL(9), VOP_GETEXTATTR(9), VOP_GETPAGES(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)
AUTHORS
This manual page was written by Doug Rabson.