Re: tail.c: 836: recheck: Assertion `valid_file_spec (f)' failed (linux, kernel 2.4.x, coreutils 5.2.1)

[Jim Meyering]

Roberto Nibali <address@hidden> wrote:
...
> If I may have your attention just for another issue while discussing tail. We
> were negatively surprised when realising that someone at some point removed 
> the
> fflush() in tail. This causes tail to behave differently than it use to IMHO 
> for
> the last 10 years and I'd like to propose following patch to address this 
> issue:
>
> --- coreutils-5.2.1-uclibc/src/tail.c-orig      2004-01-21 15:27:02.000000000 
> -0
> 700
> +++ coreutils-5.2.1-uclibc/src/tail.c   2004-12-09 02:46:37.000000000 -0700
> @@ -325,6 +325,7 @@
>    assert (fd == STDOUT_FILENO);
>    if (n_bytes > 0 && fwrite (buffer, 1, n_bytes, stdout) == 0)
>      error (EXIT_FAILURE, errno, _("write error"));
> +  else fflush(stdout);
>  }

Thanks for the suggestion, but what exactly is the problem?
There is already code to call fflush just before sleeping in tail_forever.
Is there some case in which that logic doesn't work?
It's better not to flush for every single xwrite (line of output),
since that would make tail a lot less efficient even when
not using the -f option.

Oh.  I see that this has been fixed since 5.2.1.
You can find the development version here:

  http://savannah.gnu.org/cvs/?group=coreutils

> If this has come up before, I'd like to get some pointers on why this feature
> was introduced and why there is no backwards compatibility flag or environment
> variable; it certainly isn't specified in either of the POSIX standards to my
> avail. I vaguely remember the same issue a couple of years ago with the tail
> provided by SunOS. Let's not repeat history ;).