From: "SZEDER Gábor" <szeder.dev@gmail.com>
To: Patrick Steinhardt <ps@pks.im>
Cc: Junio C Hamano <gitster@pobox.com>, git@vger.kernel.org
Subject: Re: [PATCH] refs: implement reference transaction hooks
Date: Sun, 7 Jun 2020 22:12:33 +0200 [thread overview]
Message-ID: <20200607201233.GB8232@szeder.dev> (raw)
In-Reply-To: <20200603112604.GA25644@tanuki.pks.im>
On Wed, Jun 03, 2020 at 01:26:04PM +0200, Patrick Steinhardt wrote:
> On Tue, Jun 02, 2020 at 10:47:55AM -0700, Junio C Hamano wrote:
> > Patrick Steinhardt <ps@pks.im> writes:
> >
> > > The above scenario is the motivation for a set of three new hooks that
> > > reach directly into Git's reference transaction. Each of the following
> > > new hooks (currently) doesn't accept any parameters and receives the set
> > > of queued reference updates via stdin:
> >
> > Do we have something (e.g. performance measurement) to convince
> > ourselves that this won't incur unacceptable levels of overhead in
> > null cases where there is no hook installed in the repository?
>
> Not yet, but I'll try to come up with a benchmark in the next iteration.
> I guess the best way to test is to directly exercise git-update-refs, as
> it's nearly a direct wrapper around reference transactions.
>
> > > + proc.in = -1;
> > > + proc.stdout_to_stderr = 1;
> > > + proc.trace2_hook_name = hook_name;
> > > +
> > > + code = start_command(&proc);
> > > + if (code)
> > > + return code;
> > > +
> > > + sigchain_push(SIGPIPE, SIG_IGN);
> > > +
> > > + for (i = 0; i < transaction->nr; i++) {
> > > + struct ref_update *update = transaction->updates[i];
> > > +
> > > + strbuf_reset(&buf);
> > > + strbuf_addf(&buf, "%s %s %s\n",
> > > + oid_to_hex(&update->old_oid),
> > > + oid_to_hex(&update->new_oid),
> > > + update->refname);
> > > +
> > > + if (write_in_full(proc.in, buf.buf, buf.len) < 0)
> > > + break;
> >
> > We leave the loop early when we detect a write failure here...
> >
> > > + }
> > > +
> > > + close(proc.in);
> > > + sigchain_pop(SIGPIPE);
> > > +
> > > + strbuf_release(&buf);
> > > + return finish_command(&proc);
> >
> > ... but the caller does not get notified. Intended?
>
> This is semi-intended. In case the hook doesn't fully consume stdin and
> exits early, writing to its stdin would fail as we ignore SIGPIPE. We
> don't want to force the hook to care about consuming all of stdin,
> though.
Why? How could the prepared hook properly initialize the voting
mechanism for the transaction without reading all the refs to be
updated?
> We could improve error handling here by ignoring EPIPE, but making every
> other write error fatal. If there's any other abnormal error condition
> then we certainly don't want the hook to act on incomplete data and
> pretend everything's fine.
As I read v2 of this patch, a prepared hook can exit(0) early without
reading all the refs to be updated, cause EPIPE in the git process
invoking the hook, and that process would interpret that as success.
I haven't though it through how such a voting mechanism would work,
but I have a gut feeling that this can't be good.
next prev parent reply other threads:[~2020-06-07 20:13 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-02 8:25 [PATCH] refs: implement reference transaction hooks Patrick Steinhardt
2020-06-02 17:47 ` Junio C Hamano
2020-06-03 11:26 ` Patrick Steinhardt
2020-06-07 20:12 ` SZEDER Gábor [this message]
2020-06-08 5:36 ` Patrick Steinhardt
2020-06-02 18:09 ` SZEDER Gábor
2020-06-03 9:46 ` Patrick Steinhardt
2020-06-03 12:27 ` [PATCH v2] refs: implement reference transaction hook Patrick Steinhardt
2020-06-03 16:51 ` Taylor Blau
2020-06-04 7:36 ` Patrick Steinhardt
2020-06-15 16:46 ` Taylor Blau
2020-06-16 5:45 ` Patrick Steinhardt
2020-06-03 17:44 ` Han-Wen Nienhuys
2020-06-03 18:03 ` Junio C Hamano
2020-06-18 10:27 ` [PATCH v3] " Patrick Steinhardt
2020-06-18 22:23 ` Junio C Hamano
2020-06-19 6:56 ` [PATCH v4] " Patrick Steinhardt
2020-10-23 1:03 ` Jeff King
2020-10-23 3:59 ` Junio C Hamano
2020-10-23 19:57 ` Taylor Blau
2020-10-23 22:07 ` Taylor Blau
2020-10-26 7:43 ` Patrick Steinhardt
2020-10-26 23:52 ` Taylor Blau
2020-10-27 5:37 ` Jeff King
2020-10-28 18:22 ` Patrick Steinhardt
2020-10-23 20:00 ` Taylor Blau
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