[Toybox] default SIGPIPE handler that calls _exit(0)?

[Isaac Dunham]

On Mon, Apr 27, 2015 at 08:36:53AM -0700, enh wrote:
> On Sun, Apr 26, 2015 at 7:30 PM, Rich Felker <dalias at libc.org> wrote:
> > On Sat, Apr 25, 2015 at 12:14:44PM -0700, enh wrote:
> >> what's the plan wrt SIGPIPE? the desktop is pretty inconsistent. many
> >> (but not all) commands install a signal handler that does _exit(0).
> >> others (coreutils 8.21's ls, say) do nothing. normally "what you do
> >> about SIGPIPE" isn't a problem but on Android that leads to a crash
> >> report and people filing "ls crashed" bugs against me. (our default
> >> shell PS setup is also noisy about crashes.)
> >
> > Why not just *block* SIGPIPE (with sigprocmask) so that the write
> > returns an error (EPIPE) and the program applies the same logic it
> > would for any other write error?
> 
> toybox does a little better than toolbox there thanks to xwrite, but
> i've yet never met anyone who checks the return value of printf...

vmstat.c, cal.c, and see xprintf().
In some places the choice of non-erroring functions is deliberate, so
that a failure to write will not lead to an early exit.

> plus there's the question of whether giving up because you're writing
> to a broken pipe is an error exit or not. you could add a special case
> to xwrite (and add xprintf and xputs and...), but since the whole idea
> is that code shouldn't have to care, it's easier just to install a
> signal handler that does _exit(0).

There are xputs and xprintf already.

Calling _exit() is wrong for toybox, since you cannot use atexit()
type code (eg, delete tempfiles on exit) - xexit() is the recommended
path for toybox.
Using a fixed return value is wrong; for an example, grep returns
0 for "line matched", 1 for "no match", and >1 for errors.

Thanks,
Isaac Dunham

 1430163005.0