walk(9P) - Plan 9 from User Space

| WALK(9P) | WALK(9P)
| NAME
| walk – descend a directory hierarchy
SYNOPSIS
| size[4] `Twalk` tag[2] fid[4] newfid[4] nwname[2] nwname*(wname[s]) size[4] `Rwalk` tag[2] nwqid[2] nwqid*(qid[13])
DESCRIPTION
| The `walk` request carries as arguments an existing fid and a proposed newfid (which must not be in use unless it is the same as fid) that the client wishes to associate with the result of traversing the directory hierarchy by ‘walking’ the hierarchy using the successive path name elements `wname`. The fid must represent a directory unless zero path name elements are specified.
The fid must be valid in the current session and must not have been opened for I/O by an `open` or `create` message. If the full sequence of `nwname` elements is walked successfully, newfid will represent the file that results. If not, newfid (and `fid`) will be unaffected. However, if newfid is in use or otherwise illegal, an `Rerror` is returned.
The name “`..`” (dot-dot) represents the parent directory. The name “`.`” (dot), meaning the current directory, is not used in the protocol.
It is legal for `nwname` to be zero, in which case newfid will represent the same file as fid and the `walk` will usually succeed; this is equivalent to walking to dot. The rest of this discussion assumes `nwname` is greater than zero.
The `nwname` path name elements `wname` are walked in order, “elementwise”. For the first elementwise walk to succeed, the file identified by fid must be a directory, and the implied user of the request must have permission to search the directory (see intro(9P)). Subsequent elementwise walks have equivalent restrictions applied to the implicit fid that results from the preceding elementwise walk.
If the first element cannot be walked for any reason, `Rerror` is returned. Otherwise, the walk will return an `Rwalk` message containing nwqid qids corresponding, in order, to the files that are visited by the nwqid successful elementwise walks; nwqid is therefore either `nwname` or the index of the first elementwise walk that failed. The value of nwqid cannot be zero unless `nwname` is zero. Also, nwqid will always be less than or equal to `nwname`. Only if it is equal, however, will newfid be affected, in which case newfid will represent the file reached by the final elementwise walk requested in the message.
A `walk` of the name “`..`” in the root directory of a server is equivalent to a walk with no name elements.
If newfid is the same as fid, the above discussion applies, with the obvious difference that if the walk changes the state of newfid, it also changes the state of fid; and if newfid is unaffected, then fid is also unaffected.
To simplify the implementation of the servers, a maximum of sixteen name elements or qids may be packed in a single message. This constant is called `MAXWELEM` in fcall(3). Despite this restriction, the system imposes no limit on the number of elements in a file name, only the number that may be transmitted in a single message.
ENTRY POINTS
| Fswalk (see 9pclient(3)) generates walk messages. One or more walk messages may be generated by any call that evaluates file names: fsopen, fsopenfd, fsdirstat, fsdirwstat.