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.