Bug#214387: libc6: writev() returns -1 with errno == 0

[Daniel Jacobowitz <dan@debian.org>]

On Mon, Oct 06, 2003 at 10:55:05AM +0200, Raphael Manfredi wrote:
> Package: libc6
> Version: 2.3.2-7
> Severity: important
> 
> I have noticed this bug since I updated to libc6 2.3.2-7.  It was not
> occurring before, with 2.3.1 (I think it was that, I don't recall).
> 
> I discovered this bug whilst using gtk-gnutella, which is opening many
> file descriptors.  At time, randomly, gtk-gnutella was crashing reporting
> an unexpected errno of 0 on a write.  I added some debugging information
> at the places where write() or writev() was occurring, something like
> (just showing the code for write(), but the same logic happens with writev):
> 
>     r = write(bio->fd, data, amount);
> 
>     if (r == -1 && errno == 0) {
>         g_warning("write(fd=%d, len=%d) returned -1 with errno = 0, "
>             "assuming EAGAIN", bio->fd, data);
>         errno = EAGAIN;
>     }
> 
> And I started to see the following warnings:
> 
>     write(fd=56, len=6386) returned -1 with errno = 0, assuming EAGAIN
> 
> in my logs.  But gtk-gnutella no longer crashed and continued (gtk-gnutella
> checks the errno on failed writes and panics if it is none of the expected
> values).
> 
> HOWEVER, this bug also randomly happens in libX11, in the XlibInt.c file.
> When a write() fails, X reports an error via its I/O reporting callback.
> Since gtk-gnutella is a GTK+ application, the GDK installs a handler via
> XSetIOErrorHandle(), which in turns logs the error, showing errno.
> 
> And its shows a line looking like this:
> 
>     Fatal IO error 0 (Success) on X server.
> 
> Looking at the code for gdk_x_io_error(), the installed callback, 0 represents
> the errno.  So the same thing happens in the libX11, where a write() returns
> -1 with an errno set to 0.
> 
> I don't think it's a kernel bug, because my kernel has not changed since
> April 2003, and I NEVER had this problem before upgrading my libc.
> 
> I tried to patch XlibInt.c to install the same workaround as I did in
> gtk-gnutella, but unfortunately, the xlibs do not compile properly on my
> machine, and anyway this problem should be fixed at the root, not by
> patching all the libraries that depend on libc!

Can we have strace output?

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer