Re: [PATCH bpf-next v2 4/5] bpftool: Read program streams through file descriptors

["Alexei Starovoitov" <alexei.starovoitov@gmail.com>]

On Thu, Sep 24, 2026 at 06:26 PM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote:
> Use bpf_prog_stream_open() in its default blocking mode when following a
> program stream. This lets bpftool wait for later output instead of exiting
> as soon as it drains the currently buffered bytes. Flush each chunk as it
> arrives so redirected output is not held in stdio buffers while the next
> read blocks.

So the same 'bpftool prog tracelog stderr PROG' prints what is buffered
and exits on old kernels and doesn't return on new ones while the prog
is loaded. Scripts that dump the stream will hang.
Probably should be opt-in?

[...]

> +	while (!stream_stop) {
> +		ret = read(fd, buf, sizeof(buf));

A signal that arrives after the stream_stop check and before read()
blocks only sets the flag. read() then sleeps until the next print or
the next signal.
exit_tracelog() calls exit(0) from the handler.
can we do the same here ?
Then stream_stop and save/restore of old[] are not needed.