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

[enh]

On Mon, Apr 27, 2015 at 9:11 AM, Rich Felker <dalias at libc.org> 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...
>>
>> 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).
>
> _exit(0) is wrong and broken. It reports success when the command did
> not succeed.

coreutils seems divided on this issue.

> Failure of the caller to recognize that it didn't succeed
> can result in data loss. If anything the right behavior for the signal
> handler would be _exit(1) not _exit(0). But I think xwrite/xprintf
> solves the issue more elegantly. Note that even if you don't check
> every printf, you still get the error status from ferror and/or fflush
> at close time (if you check them) but that might result in a lot of
> wasted cpu time if you continue processing/writing after a pipe broke.

it would also result in things like top(1) not exiting.

-- 
Elliott Hughes - http://who/enh - http://jessies.org/~enh/
Android native code/tools questions? Mail me/drop by/add me as a reviewer.

 1430151451.0