VNSUBR(9) | Kernel Developer's Manual | VNSUBR(9) |
vnsubr
, vn_close
,
vn_default_error
,
vn_isunder
, vn_lock
,
vn_marktext
, vn_rdwr
,
vn_open
, vn_stat
,
vn_writechk
— high-level
convenience functions for vnode operations
#include
<sys/param.h>
#include <sys/lock.h>
#include <sys/vnode.h>
int
vn_close
(struct
vnode *vp, int
flags, struct ucred
*cred, struct proc
*p);
int
vn_default_error
(void
*v);
int
vn_isunder
(struct
vnode *dvp, struct vnode
*rvp, struct proc
*p);
int
vn_lock
(struct
vnode *vp, int
flags);
void
vn_marktext
(struct
vnode *vp);
int
vn_open
(struct
nameidata *ndp, int
fmode, int
cmode);
int
vn_rdwr
(enum uio_rw rw,
struct vnode *vp, caddr_t base,
int len, off_t offset,
enum uio_seg segflg, int ioflg,
struct ucred *cred, size_t
*aresid, struct proc *p);
int
vn_stat
(struct
vnode *vp, struct stat
*sb, struct proc
*p);
int
vn_writechk
(struct
vnode *vp);
The high-level functions described in this page are convenience functions for simplified access to the vnode operations described in VOP_LOOKUP(9).
vn_close
(vp,
flags, cred,
p)vn_close
() simply locks the vnode, invokes the
vnode operation
VOP_CLOSE
()
and calls vput(9) to return the vnode to
the freelist or holdlist. Note that vn_close
()
expects an unlocked, referenced vnode and will dereference the vnode prior
to returning. If the operation is successful, zero is returned; otherwise
an appropriate error is returned.vn_default_error
(v)vn_isunder
(dvp,
rvp, p)vn_isunder
() is intended
to be used in chroot(2),
chdir(2),
fchdir(2), etc., to ensure that
chroot(2) actually means something. If
the operation is successful, zero is returned; otherwise 1 is
returned.vn_lock
(vp,
flags)The
vn_lock
()
function must not be called when the vnode's reference count is zero.
Instead, the vget(9) function should be
used.
In addition to the flags
accepted by VOP_LOCK(9), the
LK_RETRY
flag may be used.
LK_RETRY
causes
vn_lock
()
to return the vnode even if it has been reclaimed. It must not be used
with LK_NOWAIT
.
The
vn_lock
()
function can sleep.
vn_marktext
(vp)vn_open
(ndp,
fmode, cmode)The pathname is described in the
nameidata structure pointed to by the
ndp argument. When initializing the nameidata
structure for
vn_open
()
with NDINIT(9), the
op must be specified as 0, and the
flags may only be 0, or
KERNELPATH
. The lookup mode and flags are set
internally by vn_open
().
The arguments fmode and
cmode specify the
open(2) file mode and the access
permissions for creation.
vn_open
()
checks permissions and invokes the
VOP_OPEN(9) or
VOP_CREATE(9) vnode operations.
If the operation is successful, zero is returned; otherwise an
appropriate error code is returned.
vn_rdwr
(rw,
vp, base,
len, offset,
segflg, ioflg,
cred, aresid,
p);UIO_READ
) or write
(UIO_WRITE
) operation. The unlocked vnode is
specified by vp. The arguments
p and cred are the calling
process and its credentials. The remaining arguments specify the
uio parameters. For further information on these
parameters, see uiomove(9).vn_stat
(vp,
sb, p)vn_stat
() basically calls the vnode operation
VOP_GETATTR(9) and transfers the
contents of a vattr structure into a
struct stat. If the operation is successful, zero is
returned; otherwise an appropriate error code is returned.vn_writechk
(vp)ETXTBSY
is returned; otherwise zero is returned to
indicate that the vnode can be written to.This section describes places within the OpenBSD source tree where actual code implementing or using the vnode framework can be found. All pathnames are relative to /usr/src.
The high-level convenience functions are implemented within the files sys/kern/vfs_vnops.c and sys/sys/vnode.h.
The locking discipline is bizarre. Many vnode operations are passed locked vnodes on entry but release the lock before they exit. Discussions with Kirk McKusick indicate that locking discipline evolved out of the pre-VFS way of doing inode locking. In addition, the current locking discipline may actually save lines of code, especially if the number of file systems is fewer than the number of call sites. However, the VFS interface would require less wizardry if the locking discipline were simpler.
The locking discipline is used in some places to attempt to make a series of operations atomic (e.g., permissions check + operation). This does not work for non-local file systems that do not support locking (e.g., NFS).
Are vnode locks even necessary? The security checks can be moved into the individual file systems. Each file system can have the responsibility of ensuring that vnode operations are suitably atomic.
The LK_NOWAIT
flag does prevent the caller
from sleeping.
The locking discipline as it relates to shared locks has yet to be defined.
October 6, 2019 | OpenBSD-current |