Description:
------------
I`ve noticed that fwrite() function hangs when it copies data from a file to a pipe and fseek() has been called before it. See the code for details.

My system:
  - GNU/Linux Slackware-current on 2.6.3 kernel
  - GCC 3.3.2
  - glibc 2.3.2
  - PHP versions tested: 5.0b4 and php5-200403071430


Reproduce code:
---------------
#!/usr/local/bin/php
<?php
$mfp = fopen(tempnam('/tmp', 'test'), 'w+');
for($i=0; $i < 1024; $i++) $kilobyte .= "A";
for($i=0; $i < 100; $i++) fwrite($mfp, $kilobyte);

$process = proc_open('/bin/cat', array(0 => array('pipe', 'r'), 1 => array('pipe', 'w'), 2 => array('pipe', 'w')), $pipes);
fseek($mfp, 0);
while( TRUE ) {
    $data = fread($mfp, 65536);
    if( strlen($data) == 0 ) break;
    fwrite($pipes[0], $data);
}

proc_close($process);
?>


Expected result:
----------------
Try to guess ;-).

Actual result:
--------------
Here is the end of strace dump:

(...cut...)
pipe([7, 8])                            = 0
pipe([9, 10])                           = 0
pipe([11, 12])                          = 0
fork()                                  = 16951
close(7)                                = 0
(,,,cut...)
lseek(3, 0, SEEK_SET)                   = 0
(...cut...)
write(8, "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"..., 8192) = 8192
write(8, "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"..., 8192) = 8192
write(8, "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"..., 8192) = 8192
write(8, "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"..., 8192 <unfinished ...>

(here PHP hangs)