From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-175.mta0.migadu.com (out-175.mta0.migadu.com [91.218.175.175]) (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 11E0C10EE for ; Sat, 16 Dec 2023 01:19:57 +0000 (UTC) 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="VE9E7FSI" Message-ID: <44dc6eb4-d524-4180-8970-4eef2a9b9f58@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1702689595; 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=JAEcl4cquQqM7eNM00aJdC3UaEH8nY11mNPK2QM2iFM=; b=VE9E7FSIRJLAzUZuHofLs9TT3Y9KQsbK+p1Kyu+NtEMtWIpExzeR2wZC016p7TChKO2nDP kpXiAiBugMAS5xS3dr76b9UZcFByIvBdrA7yM1fo7kS+TFokBwiJKfV8rLar211xJib3Yr AqAK+JmMvemZcTWB6gLhGgPFp8cq6Eo= Date: Fri, 15 Dec 2023 17:19:48 -0800 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next v13 04/14] bpf: add struct_ops_tab to btf. Content-Language: en-US To: Kui-Feng Lee , thinker.li@gmail.com Cc: kuifeng@meta.com, bpf@vger.kernel.org, ast@kernel.org, song@kernel.org, kernel-team@meta.com, andrii@kernel.org, drosen@google.com References: <20231209002709.535966-1-thinker.li@gmail.com> <20231209002709.535966-5-thinker.li@gmail.com> <466399be-c571-48af-8f48-8365689d4d20@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 12/15/23 1:42 PM, Kui-Feng Lee wrote: > > > On 12/14/23 18:22, Martin KaFai Lau wrote: >> On 12/8/23 4:26 PM, thinker.li@gmail.com wrote: >>> +const struct bpf_struct_ops_desc *btf_get_struct_ops(struct btf *btf, u32 >>> *ret_cnt) >>> +{ >>> +    if (!btf) >>> +        return NULL; >>> +    if (!btf->struct_ops_tab) >> >>          *ret_cnt = 0; >> >> unless the later patch checks the return value NULL before using *ret_cnt. >> Anyway, better to set *ret_cnt to 0 if the btf has no struct_ops. >> >> The same should go for the "!btf" case above but I suspect the above !btf >> check is unnecessary also and the caller should have checked for !btf itself >> instead of expecting a list of struct_ops from a NULL btf. Lets continue the >> review on the later patches for now to confirm where the above !btf case might >> happen. > > Checking callers, I didn't find anything that make btf here NULL so far. > It is safe to remove !btf check. For the same reason as assigning > *ret_cnt for safe, this check should be fine here as well, right? If for safety, why ref_cnt is not checked for NULL also? The userspace passed-in btf should have been checked for NULL long time before reaching here. There is no need to be over protective here. It would really need a BUG_ON instead if btf was NULL here (don't add a BUG_ON though). afaict, no function in btf.c is checking the btf argument for NULL also. > > I don't have strong opinion here. What I though is to keep the values > as it is without any side-effect if the function call fails and if > possible. And, the callers should not expect the callee to set some > specific values when a call fails. For *ref_cnt stay uninit, there is a bug in patch 10 which exactly assumes 0 is set in *ret_cnt when there is no struct_ops. It is a good signal on how this function will be used. I think it is arguable whether returning NULL here is failure. I would argue getting a 0 struct_ops_desc array is not a failure. It is why the !btf case confuses the return NULL case to mean a never would happen error instead of meaning there is no struct_ops. Taking out the !btf case, NULL means there is no struct_ops (instead of failure), so 0 cnt. Anyhow, either assign 0 to *ret_cnt here, or fix patch 10 to init the local cnt 0 and write a warning comment here in btf_get_struct_ops() saying ret_cnt won't be set when there is no struct_ops in the btf. When looking at it again, how about moving the bpf_struct_ops_find_*() to btf.c. Then it will avoid the need of the new btf_get_struct_ops() function. bpf_struct_ops_find_*() can directly use the btf->struct_ops_tab. > >> >>> +        return NULL; >>> + >>> +    *ret_cnt = btf->struct_ops_tab->cnt; >>> +    return (const struct bpf_struct_ops_desc *)btf->struct_ops_tab->ops; >>> +} >>