Re: PROBLEM: fstat(2) returns st_size==0 for non-empty FIFO.

["Alejandro Riveira Fernández" <ariveira@gmail.com>]

El Tue, 9 Sep 2008 16:05:06 -0700
John Wenker <jjw@pt.com> escribió:

> A colleague has run into a problem.  We assume it's a kernel issue.  Here 
> is the pertinent bug report data.
> 
> [1.] One line summary of the problem:
> fstat(2) returns st_size == 0 for a FIFO that is known to have data in it.
> 
> [2.] Full description of the problem/report:
> When using a FIFO, fstat(2) (and stat(2)) returns a 'struct stat' with the 
> st_size field equal to zero, at a time when the FIFO is known to have data 
> in it.  Problem occurs with Linux 2.6.16 kernel (see more below), but does 
> not occur on 2.4.20.
> 
> [3.] Keywords (i.e., modules, networking, kernel):
> stat, fstat, FIFO, struct stat, st_size, system call, write
> 
> [4.] Kernel version (from /proc/version):
> Linux version 2.6.16.13-4-default (geeko@buildhost) (gcc version 4.1.0 
> (SUSE Linux)) #1 Wed May 3 04:53:23 UTC 2006
> 
> Note: Problem does _not_ occur on Linux version 2.4.20-8 
> (bhcompile@porky.devel.redhat.com) (gcc version 3.2.2 2003022 (Red Hat 
> Linux 3.2.2-5)) #1 Thu Mar 13 17:54:28 EST 2003
> 
> [5.] Output of Oops.. message (if applicable) with symbolic information 
>      resolved (see Documentation/oops-tracing.txt)
> No oops.  Problem doesn't cause system crash, only affects behavior of 
> user applications.
> 
> [6.] A small shell script or example program which triggers the
>      problem (if possible)
> I don't know if this qualifies as "small", but there is a 'C' program 
> attached that will reproduce the problem (fifo.c).

 FWIW
 $ LC_ALL=C ./fifo test
 Enter a string to write into the FIFO: Hello World!        
 fifo: WARNING - 0 (of 14 requested) bytes written into FIFO.
 0 bytes in FIFO.
 $ uname -r                                                                                
 2.6.27-rc5
                                                                                          

 
 

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