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

[Rich Felker]

On Mon, Apr 27, 2015 at 12:30:05PM -0700, Isaac Dunham wrote:
> 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.

Thanks for clarifying.

> > 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.

Agreed. _exit was only proposed because exit (or xexit) would be
invalid from a signal handler in general.

> Using a fixed return value is wrong; for an example, grep returns
> 0 for "line matched", 1 for "no match", and >1 for errors.

Agreed. This is another reason the logic needs to be local to the
tool or else xprintf/xwrite/etc. need a way to control the exit value
if they don't already have one.

Rich

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