Re: [PATCH] Call clearerr() on stdout before close_stream() is called.

[Eric Blake]

On 02/04/2016 03:46 AM, David Cantrell wrote:
> This is seen in bison and possibly other programs.  Bison will
> incorrectly receive SIGPIPE and terminate because close_stream() is
> picking up a rogue EPIPE in errno.  Before fclose(), clearerr(stdout)
> needs to be called so that the errors it will check for are for the
> immediate call of close_stream().
> ---
>  lib/closeout.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/lib/closeout.c b/lib/closeout.c
> index 311faf4..36895a2 100644
> --- a/lib/closeout.c
> +++ b/lib/closeout.c
> @@ -106,6 +106,8 @@ close_stdout_set_ignore_EPIPE (bool ignore)
>  void
>  close_stdout (void)
>  {
> +  clearerr (stdout);
> +

This part is wrong.  The whole point of close_stdout() is to detect any
error that occurred in the stream prior to closing it, not just errors
in closing the stream.

>    if (close_stream (stdout) != 0
>        && !(ignore_EPIPE && errno == EPIPE))

But you are correct that if close_stream() does not set errno, then we
may have a spurious EPIPE getting through to the second check.  Under
what conditions would close_stream() return non-zero but not set errno?

I guess I need a bit more context to what bison is doing to why it
thinks that clearing out any earlier fwrite() and similar failures prior
to the close will prevent spurious EPIPE messages.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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