walk – descend a directory hierarchy|
size Twalk tag fid newfid nwname nwname*(wname[s])|
size Rwalk tag nwqid nwqid*(qid)
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.
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.|