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<title>walk(9P) - Plan 9 from User Space</title>
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<tr><td width=20><td><b>WALK(9P)</b><td align=right><b>WALK(9P)</b>
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<p><font size=+1><b>NAME </b></font><br>
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walk – descend a directory hierarchy<br>
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<p><font size=+1><b>SYNOPSIS </b></font><br>
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<i>size</i>[4] <tt><font size=+1>Twalk</font></tt> <i>tag</i>[2] <i>fid</i>[4] <i>newfid</i>[4] <i>nwname</i>[2] <i>nwname</i>*(<i>wname</i>[<i>s</i>])<br>
<i>size</i>[4] <tt><font size=+1>Rwalk</font></tt> <i>tag</i>[2] <i>nwqid</i>[2] <i>nwqid</i>*(<i>qid</i>[13])<br>
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<p><font size=+1><b>DESCRIPTION </b></font><br>
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The <tt><font size=+1>walk</font></tt> request carries as arguments an existing <i>fid</i> and a proposed
<i>newfid</i> (which must not be in use unless it is the same as <i>fid</i>)
that the client wishes to associate with the result of traversing
the directory hierarchy by ‘walking’ the hierarchy using the successive
path name elements <tt><font size=+1>wname</font></tt>. The <i>fid</i> must represent
a directory unless zero path name elements are specified.
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The <i>fid</i> must be valid in the current session and must not have
been opened for I/O by an <tt><font size=+1>open</font></tt> or <tt><font size=+1>create</font></tt> message. If the full
sequence of <tt><font size=+1>nwname</font></tt> elements is walked successfully, <i>newfid</i> will
represent the file that results. If not, <i>newfid</i> (and <tt><font size=+1>fid</font></tt>) will
be unaffected. However, if <i>newfid</i> is in use or otherwise illegal,
an <tt><font size=+1>Rerror</font></tt> is returned.
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The name “<tt><font size=+1>..</font></tt>” (dot-dot) represents the parent directory. The name
“<tt><font size=+1>.</font></tt>” (dot), meaning the current directory, is not used in the protocol.
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It is legal for <tt><font size=+1>nwname</font></tt> to be zero, in which case <i>newfid</i> will represent
the same file as <i>fid</i> and the <tt><font size=+1>walk</font></tt> will usually succeed; this is
equivalent to walking to dot. The rest of this discussion assumes
<tt><font size=+1>nwname</font></tt> is greater than zero.
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The <tt><font size=+1>nwname</font></tt> path name elements <tt><font size=+1>wname</font></tt> are walked in order, “elementwise”.
For the first elementwise walk to succeed, the file identified
by <i>fid</i> must be a directory, and the implied user of the request
must have permission to search the directory (see <i>intro</i>(9P)).
Subsequent elementwise walks have equivalent
restrictions applied to the implicit fid that results from the
preceding elementwise walk.
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If the first element cannot be walked for any reason, <tt><font size=+1>Rerror</font></tt> is
returned. Otherwise, the walk will return an <tt><font size=+1>Rwalk</font></tt> message containing
<i>nwqid</i> qids corresponding, in order, to the files that are visited
by the <i>nwqid</i> successful elementwise walks; <i>nwqid</i> is therefore
either <tt><font size=+1>nwname</font></tt> or the index of the first elementwise
walk that failed. The value of <i>nwqid</i> cannot be zero unless <tt><font size=+1>nwname</font></tt>
is zero. Also, <i>nwqid</i> will always be less than or equal to <tt><font size=+1>nwname</font></tt>.
Only if it is equal, however, will <i>newfid</i> be affected, in which
case <i>newfid</i> will represent the file reached by the final elementwise
walk requested in the message.
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A <tt><font size=+1>walk</font></tt> of the name “<tt><font size=+1>..</font></tt>” in the root directory of a server is equivalent
to a walk with no name elements.
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If <i>newfid</i> is the same as <i>fid</i>, the above discussion applies, with
the obvious difference that if the walk changes the state of <i>newfid</i>,
it also changes the state of <i>fid</i>; and if <i>newfid</i> is unaffected,
then <i>fid</i> is also unaffected.
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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 <tt><font size=+1>MAXWELEM</font></tt> in <a href="../man3/fcall.html"><i>fcall</i>(3)</a>. 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.<br>
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<p><font size=+1><b>ENTRY POINTS </b></font><br>
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<i>Fswalk</i> (see <a href="../man3/9pclient.html"><i>9pclient</i>(3)</a>) generates walk messages. One or more
walk messages may be generated by any call that evaluates file
names: <i>fsopen</i>, <i>fsopenfd</i>, <i>fsdirstat</i>, <i>fsdirwstat</i>.<br>
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