freebsd/share/man/man9/namei.9

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.Dd December 16, 1998
.Os
.Dt NAMEI 9
.Sh NAME
.Nm namei ,
.Nm NDINIT
.Nd convert pathname to a pointer to a locked vnode.
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/namei.h>
.Ft int
.Fn namei "struct nameidata *ndp"
.Ft void
.Fn NDINIT "struct nameidata *ndp" "int operation" "int operflags" "int segflag" "const char *path" "struct proc *proc"
.Fn NDFREE "struct nameidata *ndp" "int operflags"
.Sh DESCRIPTION
.Fn namei
is used to get from a pathname to a vnode for the object.
This is a necessity to start doing VFS operations.  The vnode
returned will have its reference count increased; when you're through
with it, you have to release it using either
.Xr vrele 9
or
.Xr vput 9 ,
depending on whether you specified the LOCKLEAF flag or not.
.Pp
To initialize the nameidata struct, you usually use
.Fn NDINIT .
It takes the following arguments:
.Pp
.Bl -tag -width nameidatap
.It Ar nameidatap
pointer to the struct nameidata to initialize
.It Ar operation
The operation to have
.Fn namei
do.  The relevant operations are
.Dv LOOKUP ,
.Dv CREATE ,
.Dv DELETE ,
and
.Dv RENAME .
The latter three are just setup for those
effects; just calling
.Fn namei
will not result in
.Fn VOP_RENAME
being called.
.It Ar operflags
Operation flags.  Several of these can be effective at the same time.
.It Ar segflag
Segment indicator.  This tells if the name of the object is in
userspace (UIO_USERSPACE) or in the kernel address space (UIO_SYSSPACE).
.It Ar path
Pointer to pathname buffer (the file or directory name that will be
looked up)
.It Ar proc
Which process context to use for the
.Fn namei
locks.
.El
.Sh NAMEI OPERATION FLAGS
.Fn namei
takes the following set of 'operation flags' that influence
how it operates:
.Bl -tag -width WANTPARENT
.It Dv LOCKLEAF
Lock vnode on return.  This is a full lock of the vnode; you'll have to use
.Xr VOP_UNLOCK 9
to release the lock (or use
.Xr vput 9
to release the lock and do a
.Xr vrele 9 ,
all in one).
.It Dv LOCKPARENT
Make 
.Fn namei
also return the parent (directory) vnode (in nd.ni_dvp),
in locked state, unless the dvp is identical to the vp, in which case the dvp
is not locked per se (but may be locked due to LOCKLEAF).
If you get a lock, remember to release the lock (using
.Xr vput 9
or
.Xr VOP_UNLOCK 9
and
.Xr vrele 9 . )
.It Dv WANTPARENT
Make
.Fn namei
also return the parent (directory) vnode, in unlocked
state.  Remember to release it (using
.Xr vrele 9 . )
.It Dv NOCACHE
Avoid
.Fn namei
creating this entry in the namecache if it is not
already present.  Normally
.Fn namei
will add entries to the name cache
if they're not already there.
.It Dv FOLLOW
With this flag,
.Fn 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).
.It Dv NOOBJ
Do not call
.Fn vfs_object_create
for the returned vnode even if it is
just a VREG and we're able to (ie, it is locked).
.It Dv NOFOLLOW
Do not follow symbolic links (pseudo).
This flag is not looked for by the actual code, which looks for
FOLLOW.
NOFOLLOW is used to indicate to the source code reader that symlinks
are intentionally not followed.
.El
.Sh ALLOCATED ELEMENTS
.Bl -tag -width WANTPARENT
.It Dv ni_startdir
Where we did lookup relative to.
In the normal case, this is either the current directory or the root.
It is the current directory if the name passed in doesn't start with /
and we have not gone through any symlinks with an absolute path, and
the root otherwise.
.Pp
In this case, it is is only used by lookup(), and should not be
considered valid after a call to namei().
.Pp
If SAVESTART is set, this is set to the same as ni_dvp, with an extra
VREF().
.Pp
To block NDFREE from releasing ni_startdir when it is set, use the
flag NDF_NO_STARTDIR_RELE.
.It Dv ni_dvp
The directory vp for the directory the object we're looking up is in.
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).
.It Dv ni_vp
The vp for the target of the of the pathname exists, NULL otherwise.
The vp is returned with increased reference count (VREF'ed).  If
LOCKLEAF is set, it is also locked.
.Pp
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).
.It Dv ni_cnd.cn_pnbuf
Path name buffer.  This is allocated through zalloc(namei_zone)
and freed through zfree(namei_zone, ...).
.Pp
This is available to the caller (who must free it using
.Xr NDFREE 9 )
if SAVESTART or SAVENAME is set.
To free only the ni_cnd.cn_pnbuf, there is a special flags NDF_ONLY_PNBUF.
To not free the cnd, use the flag ND_NO_FREE_PNBUF.
.El
.Sh BUGS
LOCKPARENT does not always result in parent vp being locked (see details in
description).
This results in complications everywhere LOCKPARENT is used.
In order to solve this for the cases that include both LOCKPARENT and LOCKLEAF,
it will be necessary to go to recursive locking.
.Sh SEE ALSO
.Xr VFS 9 ,
.Xr vnode 9 ,
.Pa src/sys/kern/vfs_lookup.c
.Sh AUTHORS
This man page was written by
.An Eivind Eklund .