nameiNDINITNDFREENDHASGIANT
- pathname translation and lookup operations
SYNOPSIS
#include <sys/param.h>
#include <sys/proc.h>
#include <sys/namei.h> int
namei (struct nameidata *ndp); void
Fo NDINIT
Fa struct nameidata *ndp u_long op u_long flags
Fa enum uio_seg segflg const char *namep struct thread *td
Fc Ft void
NDFREE (struct nameidata *ndp const uint flags); int
NDHASGIANT (struct nameidata *ndp);
DESCRIPTION
The
facility allows the client to perform pathname translation and lookup
operations.
The
functions will increment the reference count for the vnode in question.
The reference count has to be decremented after use of the vnode, by
using either
vrele(9)
or
vput(9),
depending on whether the
LOCKLEAF
flag was specified or not.
If the
Giant
lock is required,
will acquire it if the caller indicates it is
MPSAFE
in which case the caller must later release
Giant
based on the results of
NDHASGIANT (.);
The
NDINIT ();
function is used to initialize
components.
It takes the following arguments:
Fa ndp
The
Vt struct nameidata
to initialize.
Fa op
The operation which
namei ();
will perform.
The following operations are valid:
LOOKUP , CREATE , DELETE
and
RENAME
The latter three are just setup for those
effects; just calling
namei ();
will not result in
VOP_RENAME ();
being called.
Fa flags
Operation flags.
Several of these can be effective at the same time.
Fa segflg
UIO segment indicator.
This indicates if the name of the object is in userspace
(UIO_USERSPACE
)
or in the kernel address space
(UIO_SYSSPACE
)
Fa namep
Pointer to the component's pathname buffer
(the file or directory name that will be looked up).
Fa td
The thread context to use for
operations and locks.
NAMEI OPERATION FLAGS
The
namei ();
function takes the following set of
``operation flags''
that influence its operation:
LOCKLEAF
Lock vnode on return.
This is a full lock of the vnode; the
VOP_UNLOCK9
should be used
to release the lock (or
vput(9)
which is equivalent to calling
VOP_UNLOCK9
followed by
vrele(9),
all in one).
LOCKPARENT
This flag lets the
namei ();
function return the parent (directory) vnode,
ni_dvp
in locked state, unless it is identical to
ni_vp
in which case
ni_dvp
is not locked per se (but may be locked due to
LOCKLEAF )
If a lock is enforced, it should be released using
vput(9)
or
VOP_UNLOCK9
and
vrele(9).
WANTPARENT
This flag allows the
namei ();
function to return the parent (directory) vnode in an unlocked state.
The parent vnode must be released separately by using
vrele(9).
MPSAFE
With this flag set,
namei ();
will conditionally acquire
Giant
if it is required by a traversed file system.
MPSAFE callers should pass the results of
NDHASGIANT ();
to
VFS_UNLOCK_GIANT
in order to conditionally release
Giant
if necessary.
NOCACHE
Avoid
namei ();
creating this entry in the namecache if it is not
already present.
Normally,
namei ();
will add entries to the name cache
if they are not already there.
FOLLOW
With this flag,
namei ();
will follow the symbolic link if the last part
of the path supplied is a symbolic link (i.e., it will return a vnode
for whatever the link points at, instead for the link itself).
NOOBJ
Do not call
vfs_object_create ();
for the returned vnode, even though it meets required criteria for VM support.
NOFOLLOW
Do not follow symbolic links (pseudo).
This flag is not looked for by the actual code, which looks for
FOLLOWNOFOLLOW
is used to indicate to the source code reader that symlinks
are intentionally not followed.
SAVENAME
Do not free the pathname buffer at the end of the
namei ();
invocation; instead, free it later in
NDFREE ();
so that the caller may access the pathname buffer.
See below for details.
SAVESTART
Retain an additional reference to the parent directory; do not free
the pathname buffer.
See below for details.
ALLOCATED ELEMENTS
The
Vt nameidata
structure is composed of the following fields:
ni_startdir
In the normal case, this is either the current directory or the root.
It is the current directory if the name passed in does not start with
`/'
and we have not gone through any symlinks with an absolute path, and
the root otherwise.
In this case, it is only used by
lookup (,);
and should not be
considered valid after a call to
namei (.);
If
SAVESTART
is set, this is set to the same as
ni_dvp
with an extra
vref(9).
To block
NDFREE ();
from releasing
ni_startdir
the
NDF_NO_STARTDIR_RELE
can be set.
ni_dvp
Vnode pointer to directory of the object on which lookup is performed.
This is available on successful return if
LOCKPARENT
or
WANTPARENT
is set.
It is locked if
LOCKPARENT
is set.
Freeing this in
NDFREE ();
can be inhibited by
NDF_NO_DVP_RELE , NDF_NO_DVP_PUT
or
NDF_NO_DVP_UNLOCK
(with the obvious effects).
ni_vp
Vnode pointer to the resulting object,
NULL
otherwise.
The
v_usecount
field of this vnode is incremented.
If
LOCKLEAF
is set, it is also locked.
Freeing this in
NDFREE ();
can be inhibited by
NDF_NO_VP_RELE , NDF_NO_VP_PUT
or
NDF_NO_VP_UNLOCK
(with the obvious effects).
ni_cnd.cn_pnbuf
The pathname buffer contains the location of the file or directory
that will be used by the
operations.
It is managed by the
uma(9)
zone allocation interface.
If the
SAVESTART
or
SAVENAME
flag is set, then the pathname buffer is available
after calling the
namei ();
function.
To only deallocate resources used by the pathname buffer,
ni_cnd.cn_pnbuf
then
NDF_ONLY_PNBUF
flag can be passed to the
NDFREE ();
function.
To keep the pathname buffer intact,
the
NDF_NO_FREE_PNBUF
flag can be passed to the
NDFREE ();
function.
An -nosplit
This manual page was written by
An Eivind Eklund Aq eivind@FreeBSD.org
and later significantly revised by
An Hiten M. Pandya Aq hmp@FreeBSD.org .
BUGS
The
LOCKPARENT
flag does not always result in the parent vnode being locked.
This results in complications when the
LOCKPARENT
is used.
In order to solve this for the cases where both
LOCKPARENT
and
LOCKLEAF
are used, it is necessary to resort to recursive locking.
Non-MPSAFE file systems exist, requiring callers to conditionally unlock
Giant
