| <head> |
| <title>read(9P) - Plan 9 from User Space</title> |
| <meta content="text/html; charset=utf-8" http-equiv=Content-Type> |
| </head> |
| <body bgcolor=#ffffff> |
| <table border=0 cellpadding=0 cellspacing=0 width=100%> |
| <tr height=10><td> |
| <tr><td width=20><td> |
| <tr><td width=20><td><b>READ(9P)</b><td align=right><b>READ(9P)</b> |
| <tr><td width=20><td colspan=2> |
| <br> |
| <p><font size=+1><b>NAME </b></font><br> |
| |
| <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> |
| |
| read, write – transfer data from and to a file<br> |
| |
| </table> |
| <p><font size=+1><b>SYNOPSIS </b></font><br> |
| |
| <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> |
| |
| <i>size</i>[4] <tt><font size=+1>Tread</font></tt> <i>tag</i>[2] <i>fid</i>[4] <i>offset</i>[8] <i>count</i>[4]<br> |
| <i>size</i>[4] <tt><font size=+1>Rread</font></tt> <i>tag</i>[2] <i>count</i>[4] <i>data</i>[<i>count</i>] |
| <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> |
| |
| <i>size</i>[4] <tt><font size=+1>Twrite</font></tt> <i>tag</i>[2] <i>fid</i>[4] <i>offset</i>[8] <i>count</i>[4] <i>data</i>[<i>count</i>]<br> |
| <i>size</i>[4] <tt><font size=+1>Rwrite</font></tt> <i>tag</i>[2] <i>count</i>[4]<br> |
| |
| </table> |
| <p><font size=+1><b>DESCRIPTION </b></font><br> |
| |
| <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> |
| |
| The <tt><font size=+1>read</font></tt> request asks for <i>count</i> bytes of data from the file identified |
| by <i>fid</i>, which must be opened for reading, starting <i>offset</i> bytes |
| after the beginning of the file. The bytes are returned with the |
| <tt><font size=+1>read</font></tt> reply message. |
| <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> |
| |
| The <i>count</i> field in the reply indicates the number of bytes returned. |
| This may be less than the requested amount. If the <i>offset</i> field |
| is greater than or equal to the number of bytes in the file, a |
| count of zero will be returned. |
| <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> |
| |
| For directories, <tt><font size=+1>read</font></tt> returns an integral number of directory |
| entries exactly as in <tt><font size=+1>stat</font></tt> (see <i>stat</i>(9P)), one for each member |
| of the directory. The <tt><font size=+1>read</font></tt> request message must have <tt><font size=+1>offset</font></tt> equal |
| to zero or the value of <tt><font size=+1>offset</font></tt> in the previous <tt><font size=+1>read</font></tt> on the directory, |
| plus the number of bytes returned in the previous |
| <tt><font size=+1>read</font></tt>. In other words, seeking other than to the beginning is illegal |
| in a directory. |
| <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> |
| |
| The <tt><font size=+1>write</font></tt> request asks that <i>count</i> bytes of data be recorded in |
| the file identified by <i>fid</i>, which must be opened for writing, |
| starting <i>offset</i> bytes after the beginning of the file. If the |
| file is append-only, the data will be placed at the end of the |
| file regardless of <i>offset</i>. Directories may not be written. |
| <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> |
| |
| The <tt><font size=+1>write</font></tt> reply records the number of bytes actually written. |
| It is usually an error if this is not the same as requested. |
| <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> |
| |
| Because 9P implementations may limit the size of individual messages, |
| more than one message may be produced by a single <i>read</i> or <i>write</i> |
| call. The <i>iounit</i> field returned by <i>open</i>(9P), if non-zero, reports |
| the maximum size that is guaranteed to be transferred atomically.<br> |
| |
| </table> |
| <p><font size=+1><b>ENTRY POINTS </b></font><br> |
| |
| <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> |
| |
| <i>Fsread</i> and <i>fswrite</i> (see <a href="../man3/9pclient.html"><i>9pclient</i>(3)</a>) generate the corresponding |
| messages. Because they take an offset parameter, the <i>fspread</i> and |
| <i>fspwrite</i> calls correspond more directly to the 9P messages. Although |
| <i>fsseek</i> affects the offset, it does not generate a message.<br> |
| |
| </table> |
| |
| <td width=20> |
| <tr height=20><td> |
| </table> |
| <!-- TRAILER --> |
| <table border=0 cellpadding=0 cellspacing=0 width=100%> |
| <tr height=15><td width=10><td><td width=10> |
| <tr><td><td> |
| <center> |
| <a href="../../"><img src="../../dist/spaceglenda100.png" alt="Space Glenda" border=1></a> |
| </center> |
| </table> |
| <!-- TRAILER --> |
| </body></html> |
