Re: [dev] ii: how to process out in a pipeline and still page with less

From: Hadrien Lacour <hadrien.lacour_AT_posteo.net>
Date: Sat, 28 May 2022 18:09:04 +0000

On Sat, May 28, 2022 at 07:58:40PM +0200, Markus Wichmann wrote:
> > You can use stdbuf(1) to modify that aspect without touching the
> > program source itself.
> >
>
> Had to look up the source for that. I had heard of stdbuf, but I always
> thought that that was impossible. How can one process change a
> process-internal detail of another program? One that is not inherited
> through fork() or exec(), I mean. Well, turns out it is impossible.
> stdbuf sets LD_PRELOAD and execs the command line, and the changing of
> the buffer modes happens in the library.
>
> That means that whole thing only works if:
> - you have the target program linked dynamically
> - you have stdbuf and the target program linked against the same libc
> - the target program doesn't change buffering modes later, anyway
> - the target program does not have elevated privilege.
>

You know what, thanks for looking it up, I also thought it was using some kind
of fork or ptrace hack. The man page doesn't even mention this =(

Now, I wonder how it'd be fixed ("it" being how does the read end of the pipe
signal to the write one the kind of buffering it wants) in a perfect world.
An environment variable read by the libc would work but is kind of ugly. A pipe
flag together with a special sh syntax would be even uglier. Hmmmm.
Received on Sat May 28 2022 - 20:09:04 CEST