WALK(5) WALK(5)
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(5)). 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 mes-
sage 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 can-
not be zero unless nwname is zero. Also, nwqid will always
be less than or equal to nwname. Only if it is equal, how-
ever, will newfid be affected, in which case newfid will
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WALK(5) WALK(5)
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 mes-
sage. This constant is called MAXWELEM in styx(2) and
styx(10.2). 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
A call to chdir(2) causes a walk. One or more walk messages
may be generated by any of the following calls, which evalu-
ate file names: bind, create, mount, open, remove, stat,
unmount, wstat. The file name element . (dot) is inter-
preted locally and is not transmitted in walk messages.
SEE ALSO
sys-bind(2), sys-chdir(2), sys-open(2), sys-remove(2), sys-
stat(2), intro(5)
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