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),
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),
VFS(9)
AUTHORS¶
This manual page was written by
Doug
Rabson.