bin/166660: [libc] [patch] New util/shlib to change per-fd
default stdio buffering mode
jhb at freebsd.org
Tue Apr 10 14:00:17 UTC 2012
The following reply was made to PR bin/166660; it has been noted by GNATS.
From: John Baldwin <jhb at freebsd.org>
To: Jeremie Le Hen <jeremie at le-hen.org>
Cc: bug-followup at freebsd.org
Subject: Re: bin/166660: [libc] [patch] New util/shlib to change per-fd default stdio buffering mode
Date: Tue, 10 Apr 2012 09:43:16 -0400
On Monday, April 09, 2012 5:21:03 pm Jeremie Le Hen wrote:
> Hi John,
> On Mon, Apr 09, 2012 at 11:30:08AM -0400, John Baldwin wrote:
> > I think it would be fine to do this in libc directly rather than via
> > LD_PRELOAD. That would let it work for static binaries as well as
> > dynamic libraries. My understanding is that this is how stdbuf works on
> > Linux (glibc honors the relevant magic environment variables). To that
> > end, I think it would be ok to move this into libc directly.
> I thought it would be too expensive to check for three (actually up to
> six, see below) in such a critical path. Moreover, this would have
> lowered a lot my chances to see this committed simply because very few
> committers would have taken the responsibility for this and the time to
> handle the debates that would have sprouted.
> Your point for static binaries is very valid but aren't you afraid of
> the performance impact? I'll try to spare some time this week to move
> libstdbuf code into libc and do some benchmarks.
Hmm, I hadn't considered the performance impact, but to be honest, this
is stdio. :) If it only happens once when stdio is first used then I think
this is fine to do in libc.
> > One more question, do you use the same environment variable as glibc for
> > this, or do you use a different scheme?
> I didn't like the GNU variable names (_STDBUF_I, _STDBUF_O and
> _STDBUF_E) so I used STDBUF_0, STDBUF_1 and STDBUF_2 instead. But the
> former are supported for obvious compatibility reasons. To be honest I
> don't really care about the names, we can use the GNU ones if you think
> it's better to avoid doing to much strcmp(3), especially if we but the
> code in the libc startup path.
If the variable values have the same semantics, then I think it is best to
simply use the same names as glibc.
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