linux-kernel - Re: [PATCH] bpf: remove pointless code from bpf_do_trace

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Date:   Thu, 22 Apr 2021 08:43:54 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Florent Revest <revest@...omium.org>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alan Maguire <alan.maguire@...cle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH] bpf: remove pointless code from bpf_do_trace_printk()

On Thu, Apr 22, 2021 at 8:35 AM Florent Revest <revest@...omium.org> wrote:
> >
> > I was having a stroll through lib/vsprintf.c and noticed bstr_printf:
> >
> >  * This function like C99 vsnprintf, but the difference is that vsnprintf gets
> >  * arguments from stack, and bstr_printf gets arguments from @bin_buf which is
> >  * a binary buffer that generated by vbin_printf.
> >
> > Maybe it would be easier to just build our argument buffer similarly
> > to what vbin_printf does.
>
> I've been experimenting with this idea and it is quite promising :) it
> also makes the code much cleaner, I find. I'll send a series asap.

You mean to use bstr_printf internally ? That could work indeed.
Make sure CONFIG_BINARY_PRINTF is selected.
CONFIG_TRACING does it already.

> BPF maintainers: should we fix forward or do you prefer reverting the
> snprintf series and then re-applying another snprintf series without
> the regression in bpf_trace_printk that mangles some argument types ?
> (bpf_seq_printf has always been like that so no regression there)

Pls send it as a follow up.
Along with another patch to clean verifier bits we discussed.
The merge window is approaching, so it has to be done asap.