linux-kernel - Re: [PATCH v4 3/9] bpf/btf: Add a function to search a member of a struct/union

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Message-Id: <20230802001824.90819c7355283843178d9163@kernel.org>
Date:   Wed, 2 Aug 2023 00:18:24 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
        linux-trace-kernel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        bpf <bpf@...r.kernel.org>, Sven Schnelle <svens@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v4 3/9] bpf/btf: Add a function to search a member of a
 struct/union

On Mon, 31 Jul 2023 19:24:25 -0700
Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> On Mon, Jul 31, 2023 at 6:15 PM Steven Rostedt <rostedt@...dmis.org> wrote:
> >
> > On Mon, 31 Jul 2023 14:59:47 -0700
> > Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
> >
> > > Assuming that is addressed. How do we merge the series?
> > > The first 3 patches have serious conflicts with bpf trees.
> > >
> > > Maybe send the first 3 with extra selftest for above recursion
> > > targeting bpf-next then we can have a merge commit that Steven can pull
> > > into tracing?
> >
> > Would it be possible to do this by basing it off of one of Linus's tags,
> > and doing the merge and conflict resolution in your tree before it gets to
> > Linus?
> >
> > That way we can pull in that clean branch without having to pull in
> > anything else from BPF. I believe Linus prefers this over having tracing
> > having extra changes from BPF that are not yet in his tree. We only need
> > these particular changes, we shouldn't be pulling in anything specific for
> > BPF, as I believe that will cause issues on Linus's side.
> 
> We can try, but I suspect git tricks won't do it.
> Masami's changes depend on patches for kernel/bpf/btf.c that
> are already in bpf-next, so git would have to follow all commits
> that touch this file. 

This point is strange. I'm working on probe/fixes which is based on
v6.5-rc3, so any bpf-next change should not be involved. Can you recheck
this point?

> I don't think git is smart enough to
> thread the needle and split the commit into files. If one commit touches
> btf.c and something else that whole commit becomes a dependency
> that pulls another commit with all files touched by
> the previous commit and so on.

As far as I understand Steve's method, we will have an intermediate branch
on bpf or probe tree, like 

linus(some common commit) ---- probes/btf-find-api

and merge it to both bpf-next and probes/for-next branch

          +----------------------bpf-next --- (merge bpf patches)
         /                       / merge
common -/\ probes/btf-find-api -/-\
          \                        \ merge
           +----------------------probes/for-next --- (merge probe patches)

Thus, we can merge both for-next branches at next merge window without
any issue. (But, yes, this is not simple, and needs maxium care)

Thank you,

> tbh for this set, the easiest for everyone, is to land the whole thing
> through bpf-next, since there are no conflicts on fprobe side.

-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>