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NAMEI(9) Kernel Developer's Manual NAMEI(9) NAME namei, NDINIT, NDINIT_AT, NDFREE_PNBUF -- pathname translation and lookup operations SYNOPSIS #include <sys/param.h> #include <sys/fcntl.h> #include <sys/namei.h> int namei(struct nameidata *ndp); void NDINIT(struct nameidata *ndp, enum nameiop op, u_int64_t flags, enum uio_seg segflg, const char *namep); void NDINIT_AT(struct nameidata *ndp, enum nameiop op, u_int64_t flags, enum uio_seg segflg, const char *namep, int dirfd); void NDFREE_PNBUF(struct nameidata *ndp); DESCRIPTION The namei facility allows the client to perform pathname translation and lookup operations. The namei functions will increment the refer- ence 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. The NDINIT() macro is used to initialize namei components. It takes the following arguments: ndp A pointer to the struct nameidata to initialize. op The operation which namei() will perform. The following opera- tions are valid: LOOKUP, CREATE, DELETE, and RENAME. The lat- ter three are just setup for those effects; just calling namei() will not result in VOP_RENAME() being called. flags Operation flags, described in the next section. Several of these can be effective at the same time. segflg UIO segment indicator. This indicates if the name of the ob- ject is in userspace (UIO_USERSPACE) or in the kernel address space (UIO_SYSSPACE). namep Pointer to the component's pathname buffer (the file or direc- tory name that will be looked up). The NDINIT_AT() macro is similar to NDINIT(), but takes one extra argu- ment: dirfd File descriptor referencing a directory, or the special value AT_FDCWD meaning the calling thread's current working direc- tory. Lookups will be performed relative to this directory. The NDFREE_PNBUF() macro is used to free the pathname buffer. It must be called exactly once for each successful namei() call. It takes the following argument: ndp A pointer to a struct nameidata that was used in a successful namei() call. NAMEI OPERATION FLAGS The namei() function takes the following set of "operation flags" that influence its operation: NC_NOMAKEENTRY An alias for NOCACHE. NC_KEEPPOSENTRY Keep the positive-caching entry in cache. This flag is typically combined with NOCACHE to not cache a new entry, but keep existing one, or with MAKEENTRY. 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. LOCKLEAF Lock vnode on return with LK_EXCLUSIVE unless LOCKSHARED is also set. VOP_UNLOCK(9) should be used to release the lock (or vput(9) which is equivalent to calling VOP_UNLOCK(9) 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_UNLOCK(9) 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). FAILIFEXISTS Makes the namei operation fail if the target exists. It requires that the LOCKPARENT flag is set and LOCKLEAF is not. 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). EMPTYPATH For namei call initialized with NDINIT_AT(), allow the namep path to be empty. In this case, the dirfd file descriptor may reference a file of arbitrary type, not necessary a directory, and lookup returns the vnode for this file. LOCKSHARED Lock vnode on return with LK_SHARED, if permitted by the file system that owns the vnode. The file system must explicitly permit this by setting MNTK_LOOKUP_SHARED in mp->mnt_kern_flag during mount and by calling VN_LOCK_ASHARE() when allocating the vnode. If LOCKLEAF is specified but shared locking is not permitted, then the vnode will be returned with LK_EXCLUSIVE. VOP_UNLOCK(9) should be used to release the lock (or vput(9) which is equivalent to calling VOP_UNLOCK(9) followed by vrele(9), all in one). 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 fol- lowed. RBENEATH Requires that namei did not cross the dirfd directory. The flag is used to implement O_RESOLVE_BENEATH flag for openat(2). NAMEILOOKUP The component is embedded in a namei lookup structure, and the vfs_lookup_nameidata() function can be used to obtain that structure. This can be useful in VOP_LOOKUP(9) implementations which need to obtain ex- tra lookup metadata. PARAMETERS DESCRIPTORS FLAGS These flags are used for several purposes. Some of them affects the global namei operation, some provide information for processing of the specific path element, for instance, by the VOP_LOOKUP implementation of the involved filesystem. RDONLY Specifies that the lookup should act as if the final node is located on read-only mount. The flag is typi- cally used by file servers, e.g. NFS, to handle read- only exports. ISRESTARTED The namei was restarted with NDRESTART(). This is used internally for double-root lookups used by ABI subsys- tems, after the lookup with native root failed. The components are reset to the original values, and lookup is repeated with different root, once. IGNOREWHITEOUT Ignore whiteouts, e.g. when checking if a directory is empty. ISWHITEOUT The result of lookup is whiteout. DOWHITEOUT Handle whiteouts, the instruction for the VOP_LOOKUP() filesystem methods. WILLBEDIR The lookup is done for creating a new entry that will be directory. It allows the trailing slash in the path string. ISOPEN The caller is the code that opens a file. This allows to weaken the lock mode of the return vnode, if the mount point indicates extended shared lock support. NOCROSSMOUNT Do not cross mount points during lookup. For ".." lookup leading to mount root, returns the root vnode of the mount instead of the covered vnode of the filesystem where the mount was placed. For other lookups passing over mount, do not jump into the mounted filesystem. This allows to descend into the file hierarchy otherwise shadowed by the mount point. NOMACCHECK Do not perform MAC checks during lookup. AUDITVNODE1 Audit the looked up vnode information, use the first slot for audit information. AUDITVNODE2 Same as AUDITVNODE1 but use the second slot. NOCAPCHECK Do not perform capability checks. If the calling process is in capability mode, lookup is denied out- right. OPENREAD The lookup was for open and file will be opened for read. OPENWRITE The lookup was for open and file will be opened for write. WANTIOCTLCAPS Leave ioctl caps for the caller. See the description of namei results. OPENNAMED Opening a named attribute (directory). NOEXECCHECK Do not perform check for allowed execution on the starting directory. It is used to implement the POSIX- required semantic for openat(2) lookups that must use the permissions from time the directory was opened, and not when used for lookup. MAKEENTRY Looked-up entry is to be added to name cache. ISSYMLINK Current component is symlink, and it needs the inter- pretation according to the FOLLOW or NOFOLLOW flags. ISLASTCN This is last component of pathname. It is handled spe- cially, many flags augment its processing. ISDOTDOT Current component name is "..". Usually implies a need to specially handle the vnode locking for instantiation of the target vnode. The generic vn_vget_ino_gen() function and its more specialized variant vn_vget_ino() might be useful. TRAILINGSLASH Path ended in a slash. CREATENAMED Create a named attribute dir. ALLOCATED ELEMENTS The nameidata structure is composed of the following fields: ni_startdir In the normal case, this is either the current direc- tory 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 vfs_lookup(), and should not be considered valid after a call to namei(). 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. 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. ni_cnd.cn_pnbuf The pathname buffer contains the location of the file or directory that will be used by the namei opera- tions. It is managed by the uma(9) zone allocation interface. RESULTS The struct namei member ni_resflags returns the following flags giving some details of the succesfull operation: NIRES_ABS The path passed was absolute. NIRES_STRICTREL Restricted lookup result. Only relative lookups were done to resolve the path to vnode. NIRES_EMPTYPATH The EMPTYPATH flag was provided and used. In particu- lar, the passed path was empty. If the WANTIOCTLCAPS flag was specified, on return the ni_filecaps mem- ber of the struct namei contains the capabilities of the file descrip- tor used as the lookup starting point (dirfd). RETURN VALUES If successful, namei() will return 0, otherwise it will return an er- ror. FILES src/sys/kern/vfs_lookup.c EXAMPLES Assuming the path variable contains a pointer to userspace path string, the following example looks up the file named by it, and performs re- quired error and resource handling: char *path; struct nameidata nd; int error; NDINIT(&nd, LOOKUP, FOLLOW | LOCKLEAF | AUDITVNODE1, UIO_USERSPACE, path); if ((error = namei(&nd)) != 0) return (error); NDFREE_PNBUF(&nd); ... use nd.ni_vp vnode ERRORS Errors which namei() may return: [ENOTDIR] A component of the specified pathname is not a di- rectory when a directory is expected. [ENAMETOOLONG] A component of a pathname exceeded 255 characters, or an entire pathname exceeded 1023 characters. [ENOENT] A component of the specified pathname does not ex- ist, or the pathname is an empty string. [EACCES] An attempt is made to access a file in a way forbid- den by its file access permissions. [ELOOP] Too many symbolic links were encountered in trans- lating the pathname. [EISDIR] An attempt is made to open a directory with write mode specified. [EINVAL] The last component of the pathname specified for a DELETE or RENAME operation is `.'. [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), vrele(9) AUTHORS This manual page was written by Eivind Eklund <eivind@FreeBSD.org> and later significantly revised by Hiten M. Pandya <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. FreeBSD 15.0 September 30, 2025 NAMEI(9)
NAME | SYNOPSIS | DESCRIPTION | NAMEI OPERATION FLAGS | PARAMETERS DESCRIPTORS FLAGS | ALLOCATED ELEMENTS | RESULTS | RETURN VALUES | FILES | EXAMPLES | ERRORS | SEE ALSO | AUTHORS | BUGS
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