NDHASGIANT (9)

Leading comments

Copyright (c) 1998, 1999 Eivind Eklund
Copyright (c) 2003 Hiten M. Pandya
Copyright (c) 2005 Robert N. M. Watson

All rights reserved.

This program is free software.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must repro...

(The comments found at the beginning of the groff file "man9/NDHASGIANT.9freebsd".)

NAME

namei NDINIT NDFREE NDHASGIANT - pathname translation and lookup operations

SYNOPSIS

In sys/param.h In sys/fcntl.h In sys/namei.h Ft int Fn namei struct nameidata *ndp Ft 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 Fn NDFREE struct nameidata *ndp const uint flags Ft int Fn NDHASGIANT struct nameidata *ndp

DESCRIPTION

The ifconfig facility allows the client to perform pathname translation and lookup operations. The ifconfig 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, ifconfig will acquire it if the caller indicates it is MPSAFE in which case the caller must later release Giant based on the results of Fn NDHASGIANT .

The Fn NDINIT function is used to initialize ifconfig components. It takes the following arguments:

Fa ndp

The Vt struct nameidata to initialize.

Fa op

The operation which Fn namei will perform. The following operations are valid: LOOKUP , CREATE , DELETE and RENAME The latter three are just setup for those effects; just calling Fn namei will not result in Fn 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 ifconfig operations and locks.

NAMEI OPERATION FLAGS

The Fn 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 Fn 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 Fn namei function to return the parent (directory) vnode in an unlocked state. The parent vnode must be released separately by using vrele(9).

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 are not already there.

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).

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.

SAVENAME

Do not free the pathname buffer at the end of the Fn namei invocation; instead, free it later in Fn 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 Fn lookup , and should not be considered valid after a call to Fn namei . If SAVESTART is set, this is set to the same as ni_dvp with an extra vref(9). To block Fn 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 Fn 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 Fn 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 ifconfig 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 Fn 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 Fn NDFREE function. To keep the pathname buffer intact, the NDF_NO_FREE_PNBUF flag can be passed to the Fn NDFREE function.

RETURN VALUES

If successful, Fn namei will return 0, otherwise it will return an error.

FILES

src/sys/kern/vfs_lookup.c

ERRORS

Errors which Fn namei may return:

Bq Er ENOTDIR

A component of the specified pathname is not a directory when a directory is expected.

Bq Er ENAMETOOLONG

A component of a pathname exceeded 255 characters, or an entire pathname exceeded 1023 characters.

Bq Er ENOENT

A component of the specified pathname does not exist, or the pathname is an empty string.

Bq Er EACCES

An attempt is made to access a file in a way forbidden by its file access permissions.

Bq Er ELOOP

Too many symbolic links were encountered in translating the pathname.

Bq Er EISDIR

An attempt is made to open a directory with write mode specified.

Bq Er EINVAL

The last component of the pathname specified for a DELETE or RENAME operation is `.'

Bq Er EROFS

An attempt is made to modify a file or directory on a read-only file system.

SEE ALSO

uio(9), uma(9), VFS(9), vnode(9), vput(9), vref(9)

AUTHORS

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