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From: "J.C. Wren" <jcwren@jcwren.com>
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To: linux-kernel@vger.kernel.org
Subject: Bug in open() function (?)
Date: Fri, 11 Jul 2003 23:09:08 -0400
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	I was playing around today and found that if an existing file is opened with 
O_TRUNC | O_RDONLY, the existing file is truncated.  This is contrary to the 
documentation for "man 2 open".  Which behavior is correct, the man page, or 
what actually happens?  Or wold this be considered a glibc/libc problem?  
This is on a stock 2.5.74 kernel.

	'man 2 open', on O_TRUNC: If  the  file already exists and is a regular file 
and the open mode allows writing (i.e., is O_RDWR or O_WRONLY) it will be 
truncated to length 0.

	--John

#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>

int main (int argc, char **argv)
{
   int fd;

   if ((fd = open ("test", O_TRUNC | O_RDONLY)) == -1)
   {
      printf ("%d:%s\n", errno, strerror (errno));
      exit (1);
   }

   close (fd);

   exit (0);
}

[bash] cc test.c
[bash] ls -l >test
[bash] ls -l test
-rw-r--r--    1 jcw      users         195 Jul 11 23:06 test
[bash] ./a.out
[bash] ls -l test
-rw-r--r--    1 jcw      users           0 Jul 11 23:06 test