179 lines
3.5 KiB
Plaintext
179 lines
3.5 KiB
Plaintext
.TH WALK 5
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.SH NAME
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walk \- descend a directory hierarchy
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.SH SYNOPSIS
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.ta \w'\fLTwalk 'u
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.IR size [4]
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.B Twalk
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.IR tag [2]
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.IR fid [4]
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.IR newfid [4]
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.IR nwname [2]
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.IR nwname *( wname [ s ])
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.br
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.IR size [4]
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.B Rwalk
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.IR tag [2]
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.IR nwqid [2]
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.IR nwqid *( qid [13])
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.SH DESCRIPTION
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The
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.B walk
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request carries as arguments an existing
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.IR fid
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and a proposed
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.I newfid
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(which must not be in use unless it is the same as
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.IR fid )
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that the client wishes to associate with
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the result of traversing the directory hierarchy
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by `walking' the hierarchy using the successive path name
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elements
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.BR wname .
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The
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.I fid
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must represent a directory unless zero path name elements are specified.
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.PP
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The
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.I fid
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must be valid in the current session and must not have been opened for I/O
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by an
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.B open
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or
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.B create
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message.
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If the full sequence of
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.B nwname
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elements is walked successfully,
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.I newfid
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will represent the file that results.
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If not,
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.I newfid
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(and
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.BR fid )
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will be unaffected.
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However, if
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.I newfid
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is in use or otherwise illegal, an
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.B Rerror
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is returned.
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.PP
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The name
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.RB `` .. ''
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(dot-dot) represents the parent directory.
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The name
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.RB `` . ''
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(dot), meaning the current directory, is not used in the protocol.
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.PP
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It is legal for
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.B nwname
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to be zero, in which case
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.I newfid
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will represent the same file as
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.I fid
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and the
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.B walk
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will usually succeed; this is equivalent to walking to dot.
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The rest of this discussion assumes
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.B nwname
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is greater than zero.
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.PP
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The
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.B nwname
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path name elements
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.B wname
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are walked in order, ``elementwise''.
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For the first elementwise walk
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to succeed, the file identified by
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.I fid
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must be a directory,
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and the implied user of the request must have permission
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to search the directory (see
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.IR intro (5)).
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Subsequent elementwise walks have equivalent restrictions
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applied to the implicit fid that results from the preceding elementwise walk.
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.PP
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If the first element cannot be walked for any reason,
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.B Rerror
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is returned.
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Otherwise, the walk will return an
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.B Rwalk
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message containing
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.I nwqid
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qids corresponding, in order, to the files that are visited by the
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.I nwqid
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successful elementwise walks;
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.I nwqid
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is therefore either
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.B nwname
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or the index of the first elementwise walk that failed.
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The value of
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.I nwqid
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cannot be zero unless
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.B nwname
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is zero.
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Also,
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.I nwqid
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will always be less than or equal to
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.BR nwname .
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Only if it is equal, however, will
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.I newfid
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be affected, in which case
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.I newfid
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will represent the file
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reached by the final elementwise walk requested in the message.
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.PP
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A
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.B walk
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of the name
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.RB `` .. ''
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in the root directory of a server is equivalent to a walk with no name elements.
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.PP
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If
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.I newfid
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is the same as
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.IR fid ,
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the above discussion applies, with the obvious difference
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that if the walk changes the state of
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.IR newfid ,
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it also changes the state of
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.IR fid ;
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and if
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.I newfid
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is unaffected, then
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.I fid
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is also unaffected.
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.PP
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To simplify the implementation of the servers, a maximum of sixteen name elements or qids
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may be packed in a single message.
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This constant is called
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.B MAXWELEM
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in
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.IR fcall (2).
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Despite this restriction, the system imposes no limit on the number of elements in a file name,
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only the number that may be transmitted in a single message.
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.SH ENTRY POINTS
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A call to
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.IR chdir (2)
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causes a
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.BR walk .
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One or more
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.B walk
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messages may be generated by
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any of the following calls, which evaluate file names:
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.IR bind ,
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.IR create ,
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.IR exec ,
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.IR mount ,
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.IR open ,
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.IR remove ,
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.IR stat ,
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.IR unmount ,
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.IR wstat .
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The file name element
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.B .
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(dot) is interpreted locally and
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is not transmitted in
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.B walk
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messages.
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