Modify buffering of standard streams via environment variables (not LD_PRELOAD)?

[Pádraig Brady]

On 19/04/2024 12:36, Zachary Santer wrote:
> On Fri, Apr 19, 2024 at 5:32 AM Pádraig Brady <P@draigbrady.com> wrote:
>>
>> env variables are what I proposed 18 years ago now:
>> https://sourceware.org/bugzilla/show_bug.cgi?id=2457
> 
> And the "resistance to that" from the Red Hat people 24 years ago is
> listed on a website that doesn't exist anymore.
> 
> If I'm to argue with a guy from 18 years ago...
> 
> Ulrich Drepper wrote:
>> Hell, no.  Programs expect a certain buffer mode and perhaps would work
>> unexpectedly if this changes.  By setting a mode to unbuffered, for instance,
>> you can easily DoS a system.  I can think about enough other reasons why this is
>> a terrible idea.  Programs explicitly must request a buffering scheme so that it
>> matches the way the program uses the stream.
> 
> If buffering were set according to the env vars before the program
> configures buffers on its end, if it chooses to, then the env vars
> have no effect. This is how the stdbuf util works, right now. Would
> programs that expect a certain buffer mode not set that mode
> explicitly themselves? Are you allowing untrusted users to set env
> vars for important daemons or something? How is this a valid concern?
> 
> This is specific to the standard streams, 0-2. Buffering of stdout and
> stderr is already configured dynamically by libc. If it's going to a
> terminal, it's line-buffered. If it's not, it's fully buffered.

Playing devil's advocate, I guess programs may be depending
on the automatic buffering modes set.
I guess the thinking is that it was too easy to perturb
the system with env vars, though you can already do that with LD_PRELOAD.

Perhaps at this stage we should consider stdbuf ubiquitous enough to suffice,
noting that it's also supported on FreeBSD.
I'm surprised that the LD_PRELOAD setting is breaking your ada build,
and it would be interesting to determine the reason for that.

cheers,
Pádraig