term% cat index.txt WALK(5) File Formats Manual 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 el‐
ements 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 proto‐
col.
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 equiva‐
lent 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, ‘‘element‐
wise''. 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 el‐
ementwise 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 re‐
turned. 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 equiva‐
lent 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(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 evaluate file names:
bind, create, exec, mount, open, remove, stat, unmount, wstat. The
file name element . (dot) is interpreted locally and is not transmit‐
ted in walk messages.
WALK(5)