.\" $OpenBSD: VOP_LOOKUP.9,v 1.41 2018/04/28 03:13:04 visa Exp $
.\"
.\" Copyright (c) 2003 Ted Unangst
.\" Copyright (c) 2000, 2001 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.Dd $Mdocdate: April 28 2018 $
.Dt VOP_LOOKUP 9
.Os
.Sh NAME
.Nm VOP_LOOKUP ,
.Nm VOP_ABORTOP ,
.Nm VOP_ACCESS ,
.Nm VOP_ADVLOCK ,
.Nm VOP_BMAP ,
.Nm VOP_BWRITE ,
.Nm VOP_CLOSE ,
.Nm VOP_CREATE ,
.Nm VOP_FSYNC ,
.Nm VOP_GETATTR ,
.Nm VOP_INACTIVE ,
.Nm VOP_IOCTL ,
.Nm VOP_ISLOCKED ,
.Nm VOP_KQFILTER ,
.Nm VOP_LINK ,
.Nm VOP_LOCK ,
.Nm VOP_MKDIR ,
.Nm VOP_MKNOD ,
.Nm VOP_OPEN ,
.Nm VOP_PATHCONF ,
.Nm VOP_POLL ,
.Nm VOP_PRINT ,
.Nm VOP_READ ,
.Nm VOP_READDIR ,
.Nm VOP_READLINK ,
.Nm VOP_RECLAIM ,
.Nm VOP_REMOVE ,
.Nm VOP_RENAME ,
.Nm VOP_REVOKE ,
.Nm VOP_RMDIR ,
.Nm VOP_SETATTR ,
.Nm VOP_STRATEGY ,
.Nm VOP_SYMLINK ,
.Nm VOP_UNLOCK ,
.Nm VOP_WRITE
.Nd vnode operations
.Sh SYNOPSIS
.In sys/vnode.h
.Ft int
.Fo VOP_ABORTOP
.Fa "struct vnode *dvp"
.Fa "struct componentname *cnp"
.Fc
.Ft int
.Fo VOP_ACCESS
.Fa "struct vnode *vp"
.Fa "int mode"
.Fa "struct ucred *cred"
.Fa "struct proc *p"
.Fc
.Ft int
.Fo VOP_ADVLOCK
.Fa "struct vnode *vp"
.Fa "void *id"
.Fa "int op"
.Fa "struct flock *fl"
.Fa "int flags"
.Fc
.Ft int
.Fo VOP_BMAP
.Fa "struct vnode *vp"
.Fa "daddr_t bn"
.Fa "struct vnode **vpp"
.Fa "daddr_t *bnp"
.Fa "int *runp"
.Fc
.Ft int
.Fo VOP_BWRITE
.Fa "struct buf *bp"
.Fc
.Ft int
.Fo VOP_CLOSE
.Fa "struct vnode *vp"
.Fa "int fflag"
.Fa "struct ucred *cred"
.Fa "struct proc *p"
.Fc
.Ft int
.Fo VOP_CREATE
.Fa "struct vnode *dvp"
.Fa "struct vnode **vpp"
.Fa "struct componentname *cnp"
.Fa "struct vattr *vap"
.Fc
.Ft int
.Fo VOP_FSYNC
.Fa "struct vnode *vp"
.Fa "struct ucred *cred"
.Fa "int waitfor"
.Fa "struct proc *p"
.Fc
.Ft int
.Fo VOP_GETATTR
.Fa "struct vnode *vp"
.Fa "struct vattr *vap"
.Fa "struct ucred *cred"
.Fa "struct proc *p"
.Fc
.Ft int
.Fo VOP_INACTIVE
.Fa "struct vnode *vp"
.Fa "struct proc *p"
.Fc
.Ft int
.Fo VOP_IOCTL
.Fa "struct vnode *vp"
.Fa "u_long command"
.Fa "void *data"
.Fa "int fflag"
.Fa "struct ucred *cred"
.Fa "struct proc *p"
.Fc
.Ft int
.Fo VOP_ISLOCKED
.Fa "struct vnode *vp"
.Fc
.Ft int
.Fo VOP_KQFILTER
.Fa "struct vnode *vp"
.Fa "struct knote *kn"
.Fc
.Ft int
.Fo VOP_LINK
.Fa "struct vnode *dvp"
.Fa "struct vnode *vp"
.Fa "struct componentname *cnp"
.Fc
.Ft int
.Fo VOP_LOCK
.Fa "struct vnode *vp"
.Fa "int flags"
.Fc
.Ft int
.Fo VOP_LOOKUP
.Fa "struct vnode *dvp"
.Fa "struct vnode **vpp"
.Fa "struct componentname *cnp"
.Fc
.Ft int
.Fo VOP_MKDIR
.Fa "struct vnode *dvp"
.Fa "struct vnode **vpp"
.Fa "struct componentname *cnp"
.Fa "struct vattr *vap"
.Fc
.Ft int
.Fo VOP_MKNOD
.Fa "struct vnode *dvp"
.Fa "struct vnode **vpp"
.Fa "struct componentname *cnp"
.Fa "struct vattr *vap"
.Fc
.Ft int
.Fo VOP_OPEN
.Fa "struct vnode *vp"
.Fa "int mode"
.Fa "struct ucred *cred"
.Fa "struct proc *p"
.Fc
.Ft int
.Fo VOP_PATHCONF
.Fa "struct vnode *vp"
.Fa "int name"
.Fa "register_t *retval"
.Fc
.Ft int
.Fo VOP_POLL
.Fa "struct vnode *vp"
.Fa "int fflag"
.Fa "int events"
.Fa "struct proc *p"
.Fc
.Ft int
.Fo VOP_PRINT
.Fa "struct vnode *vp"
.Fc
.Ft int
.Fo VOP_READ
.Fa "struct vnode *vp"
.Fa "struct uio *uio"
.Fa "int ioflag"
.Fa "struct ucred *cred"
.Fc
.Ft int
.Fo VOP_READDIR
.Fa "struct vnode *vp"
.Fa "struct uio *uio"
.Fa "struct ucred *cred"
.Fa "int *eofflag"
.Fc
.Ft int
.Fo VOP_READLINK
.Fa "struct vnode *vp"
.Fa "struct uio *uio"
.Fa "struct ucred *cred"
.Fc
.Ft int
.Fo VOP_RECLAIM
.Fa "struct vnode *vp"
.Fa "struct proc *p"
.Fc
.Ft int
.Fo VOP_REMOVE
.Fa "struct vnode *dvp"
.Fa "struct vnode *vp"
.Fa "struct componentname *cnp"
.Fc
.Ft int
.Fo VOP_RENAME
.Fa "struct vnode *fdvp"
.Fa "struct vnode *fvp"
.Fa "struct componentname *fcnp"
.Fa "struct vnode *tdvp"
.Fa "struct vnode *tvp"
.Fa "struct componentname *tcnp"
.Fc
.Ft int
.Fo VOP_REVOKE
.Fa "struct vnode *vp"
.Fa "int flags"
.Fc
.Ft int
.Fo VOP_RMDIR
.Fa "struct vnode *dvp"
.Fa "struct vnode *vp"
.Fa "struct componentname *cnp"
.Fc
.Ft int
.Fo VOP_SETATTR
.Fa "struct vnode *vp"
.Fa "struct vattr *vap"
.Fa "struct ucred *cred"
.Fa "struct proc *p"
.Fc
.Ft int
.Fo VOP_STRATEGY
.Fa "struct buf *bp"
.Fc
.Ft int
.Fo VOP_SYMLINK
.Fa "struct vnode *dvp"
.Fa "struct vnode **vpp"
.Fa "struct componentname *cnp"
.Fa "struct vattr *vap"
.Fa "char *target"
.Fc
.Ft int
.Fo VOP_UNLOCK
.Fa "struct vnode *vp"
.Fc
.Ft int
.Fo VOP_WRITE
.Fa "struct vnode *vp"
.Fa "struct uio *uio"
.Fa "int ioflag"
.Fa "struct ucred *cred"
.Fc
.Sh DESCRIPTION
The
.Nm VOP
functions implement a generic way to perform operations on vnodes.
The VOP function called passes the arguments to the correct file system
specific function.
Not all file systems implement all operations, in which case a generic
method will be used.
These functions exist to provide an abstract method to invoke vnode
operations without needing to know anything about the underlying file system.
Many system calls map directly to a specific VOP function.
.Pp
The arguments for each VOP
function consist of one or more vnode pointers along with other data
needed to perform the operation.
Care must be taken to obey the vnode locking discipline when using
VOP functions.
Many VOP calls take a
.Vt struct proc *p
argument.
This should be the current process.
VOP calls are not safe to call in an interrupt context.
.Pp
The
.Vt vattr
structure used by
.Fn VOP_CREATE ,
.Fn VOP_GETATTR ,
.Fn VOP_MKDIR ,
.Fn VOP_MKNOD ,
.Fn VOP_SETATTR ,
and
.Fn VOP_SYMLINK
is:
.Bd -literal
struct vattr {
	enum vtype      va_type;      /* vnode type */
	mode_t          va_mode;      /* files access mode and type */
	nlink_t         va_nlink;     /* number of references */
	uid_t           va_uid;       /* owner user id */
	gid_t           va_gid;       /* owner group id */
	long            va_fsid;      /* file system id */
	long            va_fileid;    /* file id */
	u_quad_t        va_size;      /* file size in bytes */
	long            va_blocksize; /* blocksize preferred for i/o */
	struct timespec va_atime;     /* time of last access */
	struct timespec va_mtime;     /* time of last modification */
	struct timespec va_ctime;     /* time file changed */
	u_long          va_gen;       /* generation number of file */
	u_long          va_flags;     /* flags defined for file */
	dev_t           va_rdev;      /* device the vnode represents */
	u_quad_t        va_bytes;     /* bytes of held disk space */
	u_quad_t        va_filerev;   /* file modification number */
	u_int           va_vaflags;   /* operations flags */
	long            va_spare;     /* remain quad aligned */
};
.Ed
.Pp
The following sections comment on the VOP functions from the consumer's
perspective.
.Pp
.Bl -tag -width Ds -compact
.It Fn VOP_ABORTOP dvp cnp
Abort any asynchronous operations pending on the vnode
.Fa dvp
associated with the path name
.Fa cnp .
This is mostly used by internal VFS code and should not be needed by
file system implementors.
.Pp
.It Fn VOP_ACCESS vp mode cred p
Determine if the locked vnode
.Fa vp
can be accessed by the calling process
.Fa p
with credentials
.Fa cred
for the given access
.Fa mode .
.Pp
.Fa mode
may contain any of the following values:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It Dv VWRITE
check writeability
.It Dv VREAD
check readability
.It Dv VEXEC
check executability
.El
.Pp
If the access check succeeds, zero is returned; otherwise, an
appropriate error code is returned.
.Pp
.It Fn VOP_ADVLOCK vp id op fl flags
Perform advisory locking on the vnode
.Fa vp
according to the operation
.Fa op
and lock specification
.Fa fl .
.Fa id
identifies the resource holding the lock
(typically a pointer to the holding process).
.Pp
.Fa op
may be one of the following operations:
.Pp
.Bl -tag -width F_GETLK -compact -offset indent
.It Dv F_GETLK
Get the first lock that would block a lock request.
.It Dv F_SETLK
Set a lock.
.It Dv F_UNLCK
Release a lock.
.El
.Pp
.Fa flags
may contain the following flags:
.Pp
.Bl -tag -width F_POSIX -compact -offset indent
.It Dv F_WAIT
If required, block waiting to obtain an exclusive lock.
.It Dv F_POSIX
Follow POSIX locking semantics; see
.Xr fcntl 2 .
.It Dv F_FLOCK
Follow
.Xr flock 2
locking semantics.
.El
.Pp
Upon success, zero is returned; otherwise, an appropriate error code is
returned.
.Pp
.It Fn VOP_BMAP vp bn vpp bnp runp
Convert the logical block number
.Fa bn
of the file the locked vnode
.Fa vp
is associated with its physical number on-disk.
The physical block number is stored in
.Fa *bnp
on return.
.Fa vpp ,
if
.No non- Ns Dv NULL ,
will be updated to point to the vnode of the block device of which
.Fa vp
is associated.
.Fa runp ,
if
.No non- Ns Dv NULL ,
will be updated to the number of contiguous disk blocks following
.Fa *bnp .
Upon success, zero is returned; otherwise, an appropriate error code is
returned.
.Pp
.It Fn VOP_BWRITE bp
Write a file system buffer to disk.
Upon success, zero is returned; otherwise, an appropriate error code is
returned.
.Pp
.It Fn VOP_CLOSE vp fflag cred p
Close the file associated with the locked vnode
.Fa vp
with file flags
.Fa fflag
by the calling process
.Fa p
with credentials
.Fa cred .
This operation should be performed only when the file is no longer being
used.
Upon success, zero is returned; otherwise, an appropriate error code is
returned.
.Pp
.It Fn VOP_CREATE dvp vpp cnp vap
Create a new directory entry for a regular file in the directory
.Fa dvp
and return a locked, referenced vnode in
.Fa vpp .
The file name is in
.Fa cnp
and its permissions will be
.Fa vap .
.Pp
.It Fn VOP_FSYNC vp cred waitfor p
Flush any dirty buffers associated with
.Fa vp
to disk.
The vnode is locked on entry and exit.
.Fa waitfor
can be set to
.Dv MNT_WAIT
to indicate that
.Fn VOP_FSYNC
should not return until all data is written.
.Pp
.It Fn VOP_GETATTR vp vap cred p
.It Fn VOP_SETATTR vp vap cred p
Access the vnode attributes
.Fa vap
of the vnode
.Fa vp
by the calling process
.Fa p
with credentials
.Fa cred .
.Fn VOP_SETATTR
requires that
.Fa vp
be locked.
A field value for any member of
.Fa vap
of
.Dv VNOVAL
represents that the information could not be obtained by
.Fn VOP_GETATTR
or should not be changed by
.Fn VOP_SETATTR .
Upon success of obtaining or changing the attributes, zero is returned;
otherwise, an appropriate error code is returned.
All attributes are held in the
.Vt vattr
structure shown above.
.Pp
.It Fn VOP_INACTIVE vp p
Notify the underlying file system that the locked vnode
.Fa vp
is no longer in use.
The vnode will be unlocked upon return.
.Fa p
specifies the calling process.
This may happen when the vnode reference count reaches zero or
when the underlying file system has disappeared or has been forcibly
unmounted.
.Pp
Typically, the underlying file system will write any buffers associated
with
.Fa vp
to disk or delete the file entry, if need be.
The underlying file system may not necessarily release any buffers
associated with
.Fa vp
so that it can be immediately reactivated in case the file is used again.
Upon success, zero is returned; otherwise, an appropriate error code is
returned.
.Pp
.It Fn VOP_IOCTL vp command data fflag cred p
Perform the control operation
.Fa command
with additional information
.Fa data
on the vnode
.Fa vp ,
normally associated with a device,
with file flags
.Fa fflag
by the calling process
.Fa p
with credentials
.Fa cred .
Upon success, zero is returned; otherwise, an appropriate error code is
returned.
.Pp
.It Fn VOP_ISLOCKED vp
.It Fn VOP_LOCK vp flags
.It Fn VOP_UNLOCK vp
.Fn VOP_LOCK
is used internally by
.Xr vn_lock 9
to lock a vnode.
It should not be used by other file system code.
.Fn VOP_UNLOCK
unlocks a vnode.
Note the asymmetry between
.Xr vn_lock 9
and
.Fn VOP_UNLOCK .
.Pp
.Fa flags
may contain the following flags:
.Pp
.Bl -tag -width LK_RECURSEFAIL -compact -offset indent
.It Dv LK_EXCLUSIVE
Acquire an exclusive lock.
.It Dv LK_SHARED
Acquire a shared lock.
.It Dv LK_NOWAIT
Don't wait if the vnode lock is held by someone else
(may still wait on reclamation lock).
.It Dv LK_RECURSEFAIL
Attempt at recursive lock fails.
.It Dv LK_DRAIN
Used to mean something else, but is now used abused as a flag to avoid a lock
inversion deadlock in deadfs.
Do not use this, it must die.
.El
.Pp
.Fn VOP_ISLOCKED
returns one of the following values:
.Pp
.Bl -tag -width LK_EXCLUSIVE -compact -offset indent
.It Dv LK_EXCLUSIVE
.Fa vp
is locked for exclusive access by the calling thread.
.It Dv LK_EXCLOTHER
.Fa vp
is locked for exclusive access by a different thread.
.It Dv LK_SHARED
.Fa vp
is locked for shared access.
The current thread may be one of the threads that have it locked.
.It 0
.Fa vp
is not locked.
.El
.Pp
.Fn VOP_ISLOCKED
should be used cautiously, as not all file systems implement locks
effectively.
.Pp
.It Fn VOP_KQFILTER vp kn
Register the
.Xr knote 9
filtering information
.Fa kn
for the vnode
.Fa vp .
Only filters for
.Dv EVFILT_READ ,
.Dv EVFILT_WRITE ,
and
.Dv EVFILT_VNODE
will invoke this operation.
Upon success, zero is returned; otherwise, a non-zero value is returned.
.Pp
.It Fn VOP_LINK dvp vp cnp
Increase the link count for the vnode
.Fa vp .
A new entry with name
.Fa cnp
should be added to the directory
.Fa dvp .
.Fa dvp
is locked on entry and unlocked on exit.
.Pp
.It Fn VOP_LOOKUP dvp vpp cnp
Find the file corresponding to the name
.Fa cnp
in the directory
.Fa dvp
and return a vnode in
.Fa vpp .
.Fa dvp
is locked on entry and exit, and
.Fa vpp
is locked upon a successful return.
.Fa vpp
will be
.Dv NULL
on error, and
.Fa cnp->cn_flags
will be set to
.Dv PDIRUNLOCK
if
.Fa dvp
has been unlocked for an unsuccessful return.
.Pp
.It Fn VOP_MKDIR dvp vpp cnp vap
Create a new directory named by
.Fa cnp
with permissions
.Fa vattr
in the directory
.Fa dvp .
On success, the new vnode is returned locked in
.Fa vpp .
.Fa dvp
must be locked on entry and is unlocked on exit.
.Pp
.It Fn VOP_MKNOD dvp vpp cnp vap
Create a device special file with name
.Fa cnp
and attributes
.Fa vap
in the directory associated with the locked vnode
.Fa dvp .
.Fa dvp
will be unlocked on return (see
.Xr vput 9 ) .
A pointer to the new, locked vnode will be returned in
.Fa *vpp
if
.Fa vpp
is not
.Dv NULL .
Upon success, zero is returned; otherwise, an appropriate error code is
returned.
.Pp
.It Fn VOP_OPEN vp mode cred p
Open the file associated with the vnode
.Fa vp
with the access modes
.Fa mode
by the calling process
.Fa p
with credentials
.Fa cred .
.Fa mode
takes the flags described in
.Xr open 2 .
.Pp
For some underlying file systems, access permissions for the file by the
process are checked; for others, this is a no-op.
In any case, this must be called before a process can access the file.
Upon success, zero is returned; otherwise, an appropriate error code is
returned.
.Pp
.It Fn VOP_PATHCONF vp name retval
Obtain the value of the applicable POSIX configurable pathname variable (see
.Xr pathconf 2 )
specified by
.Fa name
from the locked vnode
.Fa vp .
The result is placed in
.Fa *retval .
Upon success, zero is returned; otherwise, an appropriate error code is
returned.
.Pp
.It Fn VOP_POLL vp fflag events p
Determine whether the vnode
.Fa vp
is ready to perform the operations specified by
.Fa events
(see
.Xr poll 2 )
with file flags
.Fa fflag
for the calling process
.Fa p .
The
.Fn selrecord
routine may be used to detect selection collisions for multiple
processes sleeping on the same file, waiting for I/O
to become possible, although all file systems currently assume that
I/O is always possible.
The return value specifies which operations from
.Fa events
were found to be ready, which may be performed without the need for
blocking.
.Pp
.It Fn VOP_PRINT vp
Print information about the vnode to the kernel message buffer.
It is not used normally, but exists only for debugging purposes.
.Pp
.It Fn VOP_READ vp uio ioflag cred
Copy data from the locked vnode
.Fa vp
to the buffers specified by
.Fa uio
with calling process credentials
.Fa cred .
.Pp
.Fa ioflag
may contain the following flags:
.Pp
.Bl -tag -width IO_APPEND -offset indent -compact
.It Dv IO_NDELAY
Non-blocking I/O.
.It Dv IO_UNIT
Do I/O as an atomic unit.
.El
.Pp
Upon success, zero is returned; otherwise, an appropriate error code is
returned.
.Pp
.It Fn VOP_READDIR vp uio cred eofflag
Read the contents of the directory associated with the locked vnode
.Fa vp ,
usually via
.Fn VOP_READ ,
and convert its file-system-specific format to that expected by the
.Xr getdents 2
system call, storing the result into the buffers specified by
.Fa uio .
.Fa cred
specifies the credentials of the calling process.
.Fa *eofflag
is set to a non-zero value on return once successful end-of-file for the
directory contents has been reached.
.Pp
Upon success, zero is returned; otherwise, an appropriate error code is
returned.
.Pp
.It Fn VOP_READLINK vp uio cred
Read a symbolic link and return the target's name in
.Fa uio .
.Fa vp
is locked on entry and exit and must be a symlink.
.Pp
.It Fn VOP_RECLAIM vp p
Used by
.Xr vclean 9
so that the file system has an opportunity to free memory
and perform any other cleanup activity related to
.Fa vp .
.Fa vp
is unlocked on entry and exit.
.Fn VOP_RECLAIM
should not be used by generic code.
.Pp
.It Fn VOP_REMOVE dvp vp cnp
Remove the link named
.Fa cnp
from the directory
.Fa dvp .
This file corresponds to the vnode
.Fa vp .
Both
.Fa dvp
and
.Fa vp
are locked on entry and unlocked on exit, and
each has its reference count decremented by one.
.Fn VOP_REMOVE
does not delete the file from disk unless its link count
becomes zero (for file systems which support multiple links).
.Pp
.It Fn VOP_RENAME fdvp fvp fcnp tdvp tvp tcnp
Remove the link to the file with associated vnode
.Fa fvp
and name
.Fa fcnp
in the directory with associated vnode
.Fa fdvp ,
and create a new link to the file with name
.Fa tcnp
(and associated locked vnode
.Fa tvp ,
if the file already exists) residing in the directory with the
associated locked vnode
.Fa tdvp .
.Fa fdvp ,
.Fa fvp ,
and
.Fa tvp
(if not
.Dv NULL )
will be released (see
.Xr vrele 9 )
and
.Fa tdvp
will have its reference count decremented (see
.Xr vput 9 )
on return.
If not
.Dv NULL ,
.Fa tvp
will be unlocked on return (see
.Xr vput 9 ) .
Upon success, zero is returned; otherwise, an appropriate error code is
returned.
.Pp
.It Fn VOP_REVOKE vp flags
Used by the
.Xr revoke 2
system call to prevent any further access to a vnode.
The vnode ops will be changed to those of deadfs, which returns only
errors.
.Ar vp
must be unlocked.
.Pp
.It Fn VOP_RMDIR dvp vp cnp
Remove the directory
.Fa vp
from the directory
.Fa dvp .
Both are locked on entry and unlocked on exit.
The name of the directory for removal is additionally contained in
.Fa cnp .
.Pp
.It Fn VOP_STRATEGY bp
Call the appropriate strategy function for the device backing the
buffer's vnode.
.Pp
.It Fn VOP_SYMLINK dvp vpp cnp vap target
Create a symbolic link with name
.Fa cnp
in the directory
.Fa dvp
with mode
.Fa vap .
The link will point to
.Fa target
and a vnode for it is returned in
.Fa vpp .
The directory vnode is locked on entry and unlocked on exit.
Note that unlike most VOP calls returning a vnode,
.Fn VOP_SYMLINK
does not lock or reference
.Fa vpp .
.Pp
.It Fn VOP_WRITE vp uio ioflag cred
Copy data from the buffers specified by
.Fa uio
to the locked vnode
.Fa vp
with calling process credentials
.Fa cred .
.Pp
.Fa ioflag
may contain the following flags:
.Pp
.Bl -tag -width IO_APPEND -offset indent -compact
.It Dv IO_APPEND
Perform write at the end of file.
.It Dv IO_NDELAY
Non-blocking I/O.
.It Dv IO_SYNC
Wait for I/O to complete.
.It Dv IO_UNIT
Do I/O as an atomic unit.
.El
.Pp
Upon success, zero is returned; otherwise, an appropriate error code is
returned.
.El
.Sh RETURN VALUES
The
.Nm VOP
functions return 0 to indicate success and a non-zero error code
to indicate failure.
.Sh SEE ALSO
.Xr errno 2 ,
.Xr uiomove 9 ,
.Xr vfs 9 ,
.Xr vn_lock 9 ,
.Xr vnode 9
.Sh AUTHORS
This man page was written by
.An Ted Unangst
for
.Ox .
.Sh BUGS
The locking discipline is too complex.
Refer to
.Xr vn_lock 9 .