1 058b0118 2005-01-03 devnull .TH READ 9P 
  2 058b0118 2005-01-03 devnull .SH NAME
  3 058b0118 2005-01-03 devnull read, write \- transfer data from and to a file
  4 058b0118 2005-01-03 devnull .SH SYNOPSIS
  5 058b0118 2005-01-03 devnull .ta \w'\fLTwrite 'u
  6 058b0118 2005-01-03 devnull .IR size [4]
  7 058b0118 2005-01-03 devnull .B Tread
  8 058b0118 2005-01-03 devnull .IR tag [2]
  9 058b0118 2005-01-03 devnull .IR fid [4]
 10 058b0118 2005-01-03 devnull .IR offset [8]
 11 058b0118 2005-01-03 devnull .IR count [4]
 12 058b0118 2005-01-03 devnull .br
 13 058b0118 2005-01-03 devnull .IR size [4]
 14 058b0118 2005-01-03 devnull .B Rread
 15 058b0118 2005-01-03 devnull .IR tag [2]
 16 058b0118 2005-01-03 devnull .IR count [4]
 17 058b0118 2005-01-03 devnull .IR data [ count ]
 18 058b0118 2005-01-03 devnull .PP
 19 058b0118 2005-01-03 devnull .IR size [4]
 20 058b0118 2005-01-03 devnull .B Twrite
 21 058b0118 2005-01-03 devnull .IR tag [2]
 22 058b0118 2005-01-03 devnull .IR fid [4]
 23 058b0118 2005-01-03 devnull .IR offset [8]
 24 058b0118 2005-01-03 devnull .IR count [4]
 25 058b0118 2005-01-03 devnull .IR data [ count ]
 26 058b0118 2005-01-03 devnull .br
 27 058b0118 2005-01-03 devnull .IR size [4]
 28 058b0118 2005-01-03 devnull .B Rwrite
 29 058b0118 2005-01-03 devnull .IR tag [2]
 30 058b0118 2005-01-03 devnull .IR count [4]
 31 058b0118 2005-01-03 devnull .SH DESCRIPTION
 32 058b0118 2005-01-03 devnull The
 33 058b0118 2005-01-03 devnull .B read
 34 058b0118 2005-01-03 devnull request
 35 058b0118 2005-01-03 devnull asks for
 36 058b0118 2005-01-03 devnull .I count
 37 058b0118 2005-01-03 devnull bytes of data
 38 058b0118 2005-01-03 devnull from the file identified by 
 39 058b0118 2005-01-03 devnull .IR fid ,
 40 058b0118 2005-01-03 devnull which must be opened for reading,
 41 058b0118 2005-01-03 devnull starting 
 42 058b0118 2005-01-03 devnull .I offset
 43 058b0118 2005-01-03 devnull bytes after the beginning of the file.
 44 058b0118 2005-01-03 devnull The bytes are returned with the
 45 058b0118 2005-01-03 devnull .B read
 46 058b0118 2005-01-03 devnull reply message.
 47 058b0118 2005-01-03 devnull .PP
 48 058b0118 2005-01-03 devnull The
 49 058b0118 2005-01-03 devnull .I count
 50 058b0118 2005-01-03 devnull field in the reply indicates the number of bytes returned.
 51 058b0118 2005-01-03 devnull This may be less than the requested amount.
 52 058b0118 2005-01-03 devnull If the
 53 058b0118 2005-01-03 devnull .I offset
 54 058b0118 2005-01-03 devnull field is greater than or equal to the number of bytes in the file,
 55 058b0118 2005-01-03 devnull a count of zero will be returned.
 56 058b0118 2005-01-03 devnull .PP
 57 058b0118 2005-01-03 devnull For directories,
 58 058b0118 2005-01-03 devnull .B read
 59 058b0118 2005-01-03 devnull returns an integral number of
 60 058b0118 2005-01-03 devnull directory entries exactly as in
 61 058b0118 2005-01-03 devnull .B stat
 62 058b0118 2005-01-03 devnull (see
 63 058b0118 2005-01-03 devnull .IR stat (9P)),
 64 058b0118 2005-01-03 devnull one for each member of the directory.
 65 058b0118 2005-01-03 devnull The
 66 058b0118 2005-01-03 devnull .B read
 67 058b0118 2005-01-03 devnull request message must have
 68 058b0118 2005-01-03 devnull .B offset
 69 058b0118 2005-01-03 devnull equal to zero or the value of
 70 058b0118 2005-01-03 devnull .B offset
 71 058b0118 2005-01-03 devnull in the previous
 72 058b0118 2005-01-03 devnull .B read
 73 058b0118 2005-01-03 devnull on the directory, plus the number of bytes
 74 058b0118 2005-01-03 devnull returned in the previous
 75 058b0118 2005-01-03 devnull .BR read .
 76 058b0118 2005-01-03 devnull In other words, seeking other than to the beginning
 77 058b0118 2005-01-03 devnull is illegal in a directory.
 78 058b0118 2005-01-03 devnull .PP
 79 058b0118 2005-01-03 devnull The
 80 058b0118 2005-01-03 devnull .B write
 81 058b0118 2005-01-03 devnull request asks that
 82 058b0118 2005-01-03 devnull .I count
 83 058b0118 2005-01-03 devnull bytes of data be recorded in the file identified by
 84 058b0118 2005-01-03 devnull .IR fid ,
 85 058b0118 2005-01-03 devnull which must be opened for writing, starting
 86 058b0118 2005-01-03 devnull .I offset
 87 058b0118 2005-01-03 devnull bytes after the beginning of the file.
 88 058b0118 2005-01-03 devnull If the file is append-only,
 89 058b0118 2005-01-03 devnull the data will be placed at the end of the file regardless of
 90 058b0118 2005-01-03 devnull .IR offset .
 91 058b0118 2005-01-03 devnull Directories may not be written.
 92 058b0118 2005-01-03 devnull .PP
 93 058b0118 2005-01-03 devnull The 
 94 058b0118 2005-01-03 devnull .B write
 95 058b0118 2005-01-03 devnull reply records the number of bytes actually written.
 96 058b0118 2005-01-03 devnull It is usually an error
 97 058b0118 2005-01-03 devnull if this is not the same as requested.
 98 058b0118 2005-01-03 devnull .PP
 99 058b0118 2005-01-03 devnull Because 9P implementations may limit the size of individual
100 058b0118 2005-01-03 devnull messages,
101 058b0118 2005-01-03 devnull more than one message may be produced by a single
102 058b0118 2005-01-03 devnull .I read
103 058b0118 2005-01-03 devnull or
104 058b0118 2005-01-03 devnull .I write
105 058b0118 2005-01-03 devnull call.
106 058b0118 2005-01-03 devnull The
107 058b0118 2005-01-03 devnull .I iounit
108 058b0118 2005-01-03 devnull field returned by
109 058b0118 2005-01-03 devnull .IR open (9P),
110 058b0118 2005-01-03 devnull if non-zero, reports the maximum size that is guaranteed
111 058b0118 2005-01-03 devnull to be transferred atomically.
112 058b0118 2005-01-03 devnull .SH ENTRY POINTS
113 058b0118 2005-01-03 devnull .I Fsread
114 058b0118 2005-01-03 devnull and
115 058b0118 2005-01-03 devnull .I fswrite
116 058b0118 2005-01-03 devnull (see
117 36cd4c58 2021-01-30 crossd .MR 9pclient (3) )
118 058b0118 2005-01-03 devnull generate the corresponding messages.
119 058b0118 2005-01-03 devnull Because they take an offset parameter, the
120 058b0118 2005-01-03 devnull .I fspread
121 058b0118 2005-01-03 devnull and
122 058b0118 2005-01-03 devnull .I fspwrite
123 058b0118 2005-01-03 devnull calls correspond more directly to the 9P messages.
124 058b0118 2005-01-03 devnull Although
125 058b0118 2005-01-03 devnull .I fsseek
126 058b0118 2005-01-03 devnull affects the offset, it does not generate a message.