NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/comp/os/linux/23054

Text File | 1993-01-07 | 1.8 KB | 62 lines

Newsgroups: comp.os.linux
Path: sparky!uunet!usc!zaphod.mps.ohio-state.edu!saimiri.primate.wisc.edu!usenet.coe.montana.edu!news.u.washington.edu!serval!luke.eecs.wsu.edu!hlu
From: [e-mail] (H.J. Lu)
Subject: Re: Library 4.1 bug/feature?  fopen("fifo","a") fails
Message-ID: <[e-mail]>
Sender: [e-mail] (USENET News System)
Organization: Washington State University!
References: <[e-mail]>
Date: Thu, 7 Jan 93 10:49:39 GMT
Lines: 50

In article <[e-mail]> [e-mail] writes:
>Is it a bug or a feature that fopen("fifo","a"), where "fifo" is a named
>pipe, fails with an 'illegal lseek' in the 4.1 version of the library?
>The opinion on comp.std.unix seems to be that there should be no
>problem...

That is a feature of stdio/kernel. I was told that according to ANSI
standard, fopen ("foo", "a") should do a lseek () to the end after
calling open (). But linux kernel refuses to any lseek () on
non-regular files. The fixes are

1. Change stdio such that ignore error from lseek (). I don't
   like this one.
2. Change kernel such that if a file can not lseek (), just return
   without error.
3. Change kernel such that if a file can not lseek (), just return
   with a special error which can be recognized by stdio that a
   lseek is requested on a non-suported file.
4. Change your source code to use fopen ("foo", "w').

I prefer (3). We need change one line in xxxxx__lseek () from

    return -EBADF;

to

    return -ELSEEK; or return -ESPIPE;

We can just add

#define     ELSEEK    ESPIPE

BTW, some Unices just do (2). Try this one on your Unix machines.

----
#include <stdio.h>


int main()
{
  int i;

  for (i = 0; i < 3; i++) {
   if (lseek (i, 0, 2) < 0)
     perror ("lseek");
  }
}
----

H.J.