Re: [PATCH] t5516: fail to run in verbose mode

From: Jeff King <peff@peff.net>
Date: Nov 28, 2022, 05:13 UTC
Message-ID: <Y4RDkGZE3cZFS25d@coredump.intra.peff.net>
In-Reply-To: <xmqqzgcfeik0.fsf@gitster.g>

On Fri, Nov 25, 2022 at 01:58:55PM +0900, Junio C Hamano wrote:

Show 12 quoted lines

> Jeff King <peff@peff.net> writes:
> 
> > One thing I'd worry about is buffering. One of the nice things about
> > "-v" is that there is nothing between you and the running programs, so
> > you are much less likely to be fooled about the order of events in the
> > output. Or wondering why nothing is happening because real-time output
> > seems to have stalled. But piping through "cat" may end up with weird
> > pauses while it fills up a 4k buffer. Using stdbuf could help, but
> > that's far from portable.
> 
> We could pipe to "dd bs=1 conv=fsync" (tongue-in-cheek---I think
> conv=fsync is a GNU thing).

We don't need the fsync; we are just worried about in-process buffering, not kernel-level flushing. So bs=1 is sufficient, in that it would use syscalls to read/write single bytes. It would just be horribly inefficient.

We really just want immediate partial read()/write() but with sensible buffer sizes. It would be easy to write a 5-line C program that did this if we really wanted to. I'm not entirely convinced it's worth worrying too much about, though.

-Peff