problems in kernel 2.4.20 stat() seems to return always size zero for any fifo (named pipe)

problems in kernel 2.4.20 stat() seems to return always size zero for any fifo (named pipe)

[jds]

 Hi:

I have a problem using stat() with kernel 2.4.20
The size of ANY fifo is always 0.
There is no backward compatibility.
Probably it is a kernel bug in this particular version.
The problem shows up when using the ls, stat commands.

How reproducible:
Always

Steps to Reproduce:
1. mkfifo xx
2. cat > xx &
3. cat < xx
4. ^Z
5. echo "abcd" > xx


Actual Results:  prw-rw-r--    1 kostadin kostadin        0 Feb 21 13:54 xx


Expected Results:  prw-rw-r--    1 kostadin kostadin        5 Feb 21 13:54 xx

In Kernel 2.4.18-X the RedHat work perfect, e inclusive in 2.4.20-X the Redhat
  beta 8.0.94

Helpme please.

Re: problems in kernel 2.4.20 stat() seems to return always size zero for any fifo (named pipe)

[Richard B. Johnson]

On Thu, 6 Mar 2003, jds wrote:

> 
>  Hi:
> 
> I have a problem using stat() with kernel 2.4.20
> The size of ANY fifo is always 0.
> There is no backward compatibility.
> Probably it is a kernel bug in this particular version.
> The problem shows up when using the ls, stat commands.
> 
> How reproducible:
> Always
[SNIPPED...]

Have you ever tried this before? I'm not aware that stat
or lstat is supposed to return the byte-count of a pipe
of FIFO. It certainly doesn't on my Sun SunOS 5.5.1 or
Linux 2.4.18. In fact, the Sun prevents ^Z when reading
the FIFO interactively so your script won't test it.

The second echo "abcd" >xx blocks so the pipe never
accepts anything anyway, there are never any "bytes-
in-the-pipe" that should be visible anyway. You can't
write to a pipe until a reader is reading, and if the
reader is suspended, there is no requirement for writing
to be buffered, i.e., a write to be accepted for such
a pipe.

Pipes do not work like you propose and, if they ever did,
that was the bug.

> Expected Results:  prw-rw-r--    1 kostadin kostadin        5 Feb 21 13:54 xx
> 
> In Kernel 2.4.18-X the RedHat work perfect,
> e inclusive in 2.4.20-X the Redhat
>   beta 8.0.94
>

Linux 2.4.18 does not accept writes to a pipe when a reader is
not actively reading. As such, a byte-count cannot exist.

If you have a program that expects a byte-count from a FIFO,
the program is broken. FIFOs must have readers before any
writes are accepted.

Cheers,
Dick Johnson
Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
Why is the government concerned about the lunatic fringe? Think about it.

Re: problems in kernel 2.4.20 stat() seems to return always size zero for any fifo (named pipe)

[jds]

In fact, do you have any idea of what's wrong?
I tryed to fix this in diferent ways but it doesn't seem to work.

Do you have any sugestion?



 



---------- Original Message ----------
From: "Richard B. Johnson" <root@chaos.analogic.com>
To: jds <jds@soltis.cc>
Sent: Thu, 6 Mar 2003 14:21:49 -0500 (EST)
Subject: Re: problems in kernel 2.4.20  stat() seems to return always size
zero for any fifo (named pipe)

> On Thu, 6 Mar 2003, jds wrote:
> 
> > 
> >  Hi:
> > 
> > I have a problem using stat() with kernel 2.4.20
> > The size of ANY fifo is always 0.
> > There is no backward compatibility.
> > Probably it is a kernel bug in this particular version.
> > The problem shows up when using the ls, stat commands.
> > 
> > How reproducible:
> > Always
> [SNIPPED...]
> 
> Have you ever tried this before? I'm not aware that stat
> or lstat is supposed to return the byte-count of a pipe
> of FIFO. It certainly doesn't on my Sun SunOS 5.5.1 or
> Linux 2.4.18. In fact, the Sun prevents ^Z when reading
> the FIFO interactively so your script won't test it.
> 
> The second echo "abcd" >xx blocks so the pipe never
> accepts anything anyway, there are never any "bytes-
> in-the-pipe" that should be visible anyway. You can't
> write to a pipe until a reader is reading, and if the
> reader is suspended, there is no requirement for writing
> to be buffered, i.e., a write to be accepted for such
> a pipe.
> 
> Pipes do not work like you propose and, if they ever did,
> that was the bug.
> 
> > Expected Results:  prw-rw-r--    1 kostadin kostadin        5 Feb 21 13:54 xx
> > 
> > In Kernel 2.4.18-X the RedHat work perfect,
> > e inclusive in 2.4.20-X the Redhat
> >   beta 8.0.94
> >
> 
> Linux 2.4.18 does not accept writes to a pipe when a reader is
> not actively reading. As such, a byte-count cannot exist.
> 
> If you have a program that expects a byte-count from a FIFO,
> the program is broken. FIFOs must have readers before any
> writes are accepted.
> 
> Cheers,
> Dick Johnson
> Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
> Why is the government concerned about the lunatic fringe? Think 
> about it.
------- End of Original Message -------