From: Jeff King <firstname.lastname@example.org> To: Johannes Schindelin <Johannes.Schindelin@gmx.de> Cc: Junio C Hamano <email@example.com>, Johannes Schindelin via GitGitGadget <firstname.lastname@example.org>, email@example.com, Alexandr Miloslavskiy <firstname.lastname@example.org> Subject: Re: [PATCH 1/1] vreportf(): avoid buffered write in favor of unbuffered one Date: Tue, 29 Oct 2019 09:49:32 -0400 [thread overview] Message-ID: <20191029134932.GA2843@sigill.intra.peff.net> (raw) In-Reply-To: <nycvar.QRO.email@example.com> On Tue, Oct 29, 2019 at 01:30:51PM +0100, Johannes Schindelin wrote: > > Also, this is only to help output from us that goes via vreportf() and > > other codepaths in us that use stdio to write to the standard error > > stream can still get mixed on Windows (I think the answer is yes, > > because we wouldn't need fflush() in this patch if we are covering all > > writes to the standard error stream)? > > Yes, `write()` can get interrupted, so there is still a slight chance of > interleaving. > > However, with `fprintf()`, apparently the MSVC runtime essentially > writes and flushes one character at a time, which will make it _much_ > more likely that two competing processes write interleaved messages to > `stderr`. Wow, they have truly taken "unbuffered" to a whole new level. I don't mind seeing this for all platforms, though. I can't think of any downside, and having one less moving part to contend with in our error-reporting code seems like a good thing. > > > - vsnprintf(msg, sizeof(msg), err, params); > > > + size_t off = strlcpy(msg, prefix, sizeof(msg)); > > > > Like snprintf(3) the strlcpy() and strlcat() functions return the > > total length of the string they tried to create. For strlcpy() that > > means the length of src. > > True (I misread `compat/strlcpy.c` and forgot to consult the > documentation). This length can be longer than `msg`, of course. I'd recommend xsnprintf() here. If we have a prefix longer than our vreportf() buffer, I think a BUG() is the right outcome. > I `git grep`ed and saw that only very short `prefix`es are hard-coded. > So that is a hypothetical concern. > > However, Alex also indicated his discomfort with this, so I will change > the code to account for a `prefix` that is too long (the entire error > message will be clipped away in that case, which is unfortunate, but to > be expected). I'd disagree here. Any caller sending an arbitrarily-large prefix is holding it wrong, and we'd probably want to know as soon as possible (and a BUG() is our best bet there). -Peff
next prev parent reply other threads:[~2019-10-29 13:49 UTC|newest] Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-10-28 15:00 [PATCH 0/1] Fix t5516 flakiness in Visual Studio builds Johannes Schindelin via GitGitGadget 2019-10-28 15:00 ` [PATCH 1/1] vreportf(): avoid buffered write in favor of unbuffered one Johannes Schindelin via GitGitGadget 2019-10-29 3:18 ` Junio C Hamano 2019-10-29 12:30 ` Johannes Schindelin 2019-10-29 13:49 ` Jeff King [this message] 2019-10-29 14:13 ` Johannes Schindelin 2019-10-29 14:32 ` Jeff King 2019-10-29 20:09 ` Johannes Schindelin 2019-10-30 1:43 ` Junio C Hamano 2019-10-29 16:44 ` Junio C Hamano 2019-10-29 10:38 ` SZEDER Gábor 2019-10-29 12:38 ` Johannes Schindelin 2019-10-29 13:52 ` Jeff King 2019-10-29 14:18 ` Johannes Schindelin 2019-10-29 13:37 ` [PATCH v2 0/1] Fix t5516 flakiness in Visual Studio builds Johannes Schindelin via GitGitGadget 2019-10-29 13:37 ` [PATCH v2 1/1] vreportf(): avoid relying on stdio buffering Johannes Schindelin via GitGitGadget 2019-10-29 14:21 ` Alexandr Miloslavskiy 2019-10-29 19:57 ` Johannes Schindelin 2019-10-29 20:09 ` Jeff King 2019-10-29 20:24 ` Alexandr Miloslavskiy 2019-10-29 20:11 ` Alexandr Miloslavskiy 2019-10-29 20:01 ` [PATCH v3 0/1] Fix t5516 flakiness in Visual Studio builds Johannes Schindelin via GitGitGadget 2019-10-29 20:01 ` [PATCH v3 1/1] vreportf(): avoid relying on stdio buffering Johannes Schindelin via GitGitGadget 2019-10-29 20:32 ` Jeff King 2019-10-30 8:54 ` Johannes Schindelin 2019-10-31 6:24 ` Jeff King 2019-10-31 10:26 ` Johannes Schindelin 2019-10-31 15:48 ` Jeff King 2019-11-01 18:41 ` Johannes Schindelin 2019-10-30 2:01 ` Junio C Hamano 2019-10-30 9:13 ` Johannes Schindelin 2019-10-30 10:44 ` [PATCH v4 0/1] Fix t5516 flakiness in Visual Studio builds Johannes Schindelin via GitGitGadget 2019-10-30 10:44 ` [PATCH v4 1/1] vreportf(): avoid relying on stdio buffering Johannes Schindelin via GitGitGadget 2019-11-02 4:05 ` Junio C Hamano
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