From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-180.mta1.migadu.com (out-180.mta1.migadu.com [95.215.58.180]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D038A2AD22 for ; Thu, 22 Jan 2026 02:49:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769050202; cv=none; b=jw6mjVs7fkJ8oyrfIG4Vr0pkozsetqYf1Cg/po8OA9JRnNHLeStwJ3D1C2MStZ+oC673CW+elfm2D49mmbMeHPXsAFIfY6XXJWeC3P5ZS6CGlOQ+cSXTT6+oiLbaurycVQnj5NUa4REB29S2ha1W3IkjMxmsKYPYcHHYlvxy604= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769050202; c=relaxed/simple; bh=lQRMsW/DIzakWp3Z6e8jYtTsZJehbKtDnMWY2SdS4Bk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=mxZmOork0Gr5O3FL83hE3jjVCFmdyrBEmsuRo8aasSmGe5ai9OvGOVSlsJyq1dNZUpZgsIKPA1RXoR9qxJQPYf7E10/zXdcsH0G0z4IkrwHncOU/Scp10NH6/x4YNrnKEcEAEY+YFfEJnllUWhBLc8lp0Qk7ZOkk8/AcfS8JNXQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=XSsOoHQh; arc=none smtp.client-ip=95.215.58.180 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="XSsOoHQh" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1769050196; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NAquLWkfaoXFtBTk6QgDbkMnqVzynMeysZ13SKr6Pgw=; b=XSsOoHQhH/9GrcwQQCzpjBLNAmFfeaUlMyi0zN1thH51fomXA/1qqLTaRFO5j+MJckW3YO YphtBRZXYY8oJTh4BExWHjGghEzSczZOnKtixDqF8x+G+PXuOUaKV3hc7qu8bFPGmlJf19 bMzhpvplmrWkle6vFpDjdw+NrokGgdE= From: Menglong Dong To: Menglong Dong , Andrii Nakryiko Cc: ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, davem@davemloft.net, dsahern@kernel.org, tglx@linutronix.de, mingo@redhat.com, jiang.biao@linux.dev, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH bpf-next v10 00/12] bpf: fsession support Date: Thu, 22 Jan 2026 10:49:35 +0800 Message-ID: <2026435.PYKUYFuaPT@7940hx> In-Reply-To: References: <20260115112246.221082-1-dongml2@chinatelecom.cn> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" X-Migadu-Flow: FLOW_OUT On 2026/1/22 08:09 Andrii Nakryiko write: > On Thu, Jan 15, 2026 at 3:23=E2=80=AFAM Menglong Dong wrote: > > > > Hi, all. > > > > In this version, I followed Andrii's suggestions in v9, and did many > > adjustment. > > > > overall > > ------- > > Sometimes, we need to hook both the entry and exit of a function with > > TRACING. Therefore, we need define a FENTRY and a FEXIT for the target > > function, which is not convenient. > > > > Therefore, we add a tracing session support for TRACING. Generally > > speaking, it's similar to kprobe session, which can hook both the entry > > and exit of a function with a single BPF program. > > > > We allow the usage of bpf_get_func_ret() to get the return value in the > > fentry of the tracing session, as it will always get "0", which is safe > > enough and is OK. > > > > Session cookie is also supported with the kfunc bpf_session_cookie(). > > In order to limit the stack usage, we limit the maximum number of cooki= es > > to 4. > > > > kfunc design > > ------------ > > In order to keep consistency with existing kfunc, we don't introduce new > > kfunc for fsession. Instead, we reuse the existing kfunc > > bpf_session_cookie() and bpf_session_is_return(). > > > > The prototype of bpf_session_cookie() and bpf_session_is_return() don't > > satisfy our needs, so we change their prototype by adding the argument > > "void *ctx" to them. > > > > We inline bpf_session_cookie() and bpf_session_is_return() for fsession > > in the verifier directly. Therefore, we don't need to introduce new > > functions for them. > > > > architecture > > ------------ > > The fsession stuff is arch related, so the -EOPNOTSUPP will be returned= if > > it is not supported yet by the arch. In this series, we only support > > x86_64. And later, other arch will be implemented. > > > > Changes v9 -> v10: > > * 1st patch: some small adjustment, such as use switch in > > bpf_prog_has_trampoline() > > * 2nd patch: some adjustment to the commit log and comment > > * 3rd patch: > > - drop the declaration of bpf_session_is_return() and > > bpf_session_cookie() > > - use vmlinux.h instead of bpf_kfuncs.h in uprobe_multi_session.c, > > kprobe_multi_session_cookie.c and uprobe_multi_session_cookie.c > > * 4th patch: > > - some adjustment to the comment and commit log > > - rename the prefix from BPF_TRAMP_M_ tp BPF_TRAMP_SHIFT_ >=20 > This is minor nit, but I think BPF_TRAMP_IS_RETURN_SHIFT and > BPF_TRAMP_COOKIE_INDEX_SHIFT (note added INDEX, because that's what we > store, not the cookie itself) makes more sense naming-wise and is more > natural to read. Consider updating this. Yeah, looks nice. >=20 > > - remove the definition of BPF_TRAMP_M_NR_ARGS > > - check the program type in bpf_session_filter() > > * 5th patch: some adjustment to the commit log > > * 6th patch: > > - add the "reg" to the function arguments of emit_store_stack_imm64() > > - use the positive offset in emit_store_stack_imm64() > > * 7th patch: > > - use "|" for func_meta instead of "+" > > - pass the "func_meta_off" to invoke_bpf() explicitly, instead of > > computing it with "stack_size + 8" > > - pass the "cookie_off" to invoke_bpf() instead of computing the curr= ent > > cookie index with "func_meta" > > * 8th patch: > > - split the modification to bpftool to a separate patch > > * v9: https://lore.kernel.org/bpf/20260110141115.537055-1-dongml2@china= telecom.cn/ > > >=20 > Overall this looks great, I was actually trying to apply and push it > despite those minor nits I left. But unfortunately there is some > conflict, so you'll have to rebase and resend. Hopefully just one last > time :) Haha, sounds great! I'll follow your comment and rebase, and send the next version later. Thanks you the review ;) >=20 > > Changes v8 -> v9: > > * remove the definition of bpf_fsession_cookie and bpf_fsession_is_retu= rn > > in the 4th and 5th patch > > * rename emit_st_r0_imm64() to emit_store_stack_imm64() in the 6th patch > > * v8: https://lore.kernel.org/bpf/20260108022450.88086-1-dongml2@chinat= elecom.cn/ > > [...] > > >=20