[PATCH] Re: SIGPIPE and tee

[Sam Liddicott]

Thanks - that change is great. Busybox tee now propagates SIGPIPE just like
GNU tee does by default.

Sam



On Mon, 7 Oct 2019 at 13:27, Denys Vlasenko <vda.linux at googlemail.com>
wrote:

> On Fri, Oct 4, 2019 at 11:20 AM Sam Liddicott <sam at liddicott.com> wrote:
> > nudge on this attached patch
> >
> > ---------- Forwarded message ---------
> > From: Sam Liddicott <sam at liddicott.com>
> > Date: Fri, 13 Sep 2019 at 11:15
> > Subject: Re: SIGPIPE and tee
> > To: busybox <busybox at busybox.net>
> >
> >
> > Here is a patch which invokes kill_myself_with_sig(SIGPIPE) if fwrite
> fails with errno=EPIPE.
> >
> > Quitting with a signal rather than a diagnostic output emulates GNU tee
> which is in line with the apparent reason for busybox tee in ignoring
> SIGPIPE in the first place.
>
>
> >
> > I have tested it with and without CONFIG_FEATURE_TEE_USE_BLOCK_IO=y
> >
> > As expected, dd succeeds for bs=1024 with
> CONFIG_FEATURE_TEE_USE_BLOCK_IO=y but fails for without.
> > dd fails in both cases for bs=1024000
> > tee fails in both cases
> >
> > ( sleep 2 ; dd if=/dev/zero bs=1024000 count=5 ; echo dd $? > /dev/tty ;
> ) | {
> build_output/sysroots-components/x86_64/busybox-native/bin/busybox.nosuid
> tee /dev/null ; echo tee $? >/dev/tty ; } | sleep 1
> >
> > ( sleep 2 ; dd if=/dev/zero bs=1024 count=5 ; echo dd $? > /dev/tty ; )
> | {
> build_output/sysroots-components/x86_64/busybox-native/bin/busybox.nosuid
> tee /dev/null ; echo tee $? >/dev/tty ; } | sleep 1
> >
> > A colleague has suggested that any write failure to stdout by tee ought
> to cause tee to quit, but I leave this to your consideration; something
> like this might cover both cases but I haven't tested it:
> >
> > if (fwrite(buf, 1, c, *fp) != c) {
> >   if (errno == EPIPE) kill_myself_with_sig(SIGPIPE);
> >   retval = EXIT_FAILURE;
> >   break;
> > }
> >
> > Sam
> >
> >
> > On Thu, 12 Sep 2019 at 20:03, Sam Liddicott <sam at liddicott.com> wrote:
> >>
> >> In  https://git.busybox.net/busybox/tree/coreutils/tee.c we read:
> >>
> >> /* gnu tee ignores SIGPIPE in case one of the output files is a pipe
> >> * that doesn't consume all its input.  Good idea... */
> >> signal(SIGPIPE, SIG_IGN);
> >>
> >>
> >> Sadly, this breaks POSIX SIGPIPE behaviour with respect to quitting
> when stdout (as a pipe) is closed.
> >>
> >> Despite the comment, GNU tee does not behave as the comment suggests.
>
> Exactly. GNU tee does not intercept SIGPIPE (unless -p is given).
> I'm removing SIGPIPE handling.
> Please try current git.
>
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