From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CE272C433FF for ; Tue, 13 Aug 2019 21:47:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9EF09206C2 for ; Tue, 13 Aug 2019 21:47:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="rIrJa7O3" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727065AbfHMVrg (ORCPT ); Tue, 13 Aug 2019 17:47:36 -0400 Received: from mail-qt1-f196.google.com ([209.85.160.196]:46350 "EHLO mail-qt1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726712AbfHMVrg (ORCPT ); Tue, 13 Aug 2019 17:47:36 -0400 Received: by mail-qt1-f196.google.com with SMTP id j15so14401549qtl.13 for ; Tue, 13 Aug 2019 14:47:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=S9dA/GdI5tmEIRRtpA3TOEAi+50PTMGECKOeEqJEGQ8=; b=rIrJa7O3sl+7svW2q/Lf7oNp+GNn7v+Rw6uSyvyF2VPOmPF+nRVFgjyFOmqqTs79tZ ka5t2oVJjFP8cIURcRCZix756S7tobGUniGigrIrBEx9sB/GPq0oSqWRj9mNTC+n2fOW Ixv2Crv+e0upytWnk3dBIMvNJN2HCRJ452f+B/g1sHOP3RwNfD6rTPYLl4fGfpjTYKvg lij4mT0PxBXSV2CWXVjPQ5g8uZSO4vsVXHNGUaB7/BQYECLh0hmxTJgMfjHCvaaSB0sI 7Fx9u8JIZSqILw91IWSw1kY2T3sp2+8a8wW1NwUXwy/vliEDC8CwzuKhzK34QX9zZcQe vfFQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=S9dA/GdI5tmEIRRtpA3TOEAi+50PTMGECKOeEqJEGQ8=; b=ZFNcxH/Lbg8LwEdGxng0k/F5VzjiUm7wkY1aS8vpyNlYmQSOPEb7MbBTXT3tkQeVpL 5E2Wf6eLb+H4j57Hefi+QkVcPKU/4HIFn/tge0F8lty4n0GEwrIJiOVOpduI3bnijVAR fKtdd7uHb5ZGbovOKp/zfD2JSSA9BixMOlWB1A0zYMtrSRs2UNLmyXQUAwkgW3K8VTGy BHM+f0lBhri6GkgZVl0kR3jylGq6H7mCFpGv8b0eCHklLXqEDRNiIC+GgWU/QT2oUVlL zo5CN4WmtcN9cuEp2ggBbOGBlDSV2KvwZYo0Edfm71dJxATfjnfC7idMb20XUyJkt/Yt MhtQ== X-Gm-Message-State: APjAAAUdWUQgHdhWlwGIEVKmefYjtb+UgUcX5YdUr2ULQE++ex9CB9gt IeBOrZ2tSLekbSK0q2rIj3Tw9DYnsZJHUxJe/Ao= X-Google-Smtp-Source: APXvYqwE2/51TGbuEMNT4kX/a2TSbMRCm2OBIRImHNGpPNfL58hFfg72fWmR7r6CxUPtRtrl0+vT2mOtNbI52+qN9Nc= X-Received: by 2002:aed:38c2:: with SMTP id k60mr33330692qte.83.1565732855091; Tue, 13 Aug 2019 14:47:35 -0700 (PDT) MIME-Version: 1.0 References: <20190809214642.12078-1-dxu@dxuuu.xyz> <20190809214642.12078-2-dxu@dxuuu.xyz> In-Reply-To: <20190809214642.12078-2-dxu@dxuuu.xyz> From: Song Liu Date: Tue, 13 Aug 2019 14:47:24 -0700 Message-ID: Subject: Re: [PATCH v2 bpf-next 1/4] tracing/probe: Add PERF_EVENT_IOC_QUERY_PROBE ioctl To: Daniel Xu Cc: Song Liu , Yonghong Song , Andrii Nakryiko , peterz@infraded.org, Ingo Molnar , Arnaldo Carvalho de Melo , Alexei Starovoitov , Alexander Shishkin , Jiri Olsa , Namhyung Kim , open list Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 9, 2019 at 2:48 PM Daniel Xu wrote: > > It's useful to know [uk]probe's nmissed and nhit stats. For example with > tracing tools, it's important to know when events may have been lost. > debugfs currently exposes a control file to get this information, but > it is not compatible with probes registered with the perf API. > > While bpf programs may be able to manually count nhit, there is no way > to gather nmissed. In other words, it is currently not possible to > retrieve information about FD-based probes. > > This patch adds a new ioctl that lets users query nmissed (as well as > nhit for completeness). We currently only add support for [uk]probes > but leave the possibility open for other probes like tracepoint. > > Signed-off-by: Daniel Xu > --- [...] > +int perf_uprobe_event_query(struct perf_event *event, void __user *info) > +{ > + struct perf_event_query_probe __user *uquery = info; > + struct perf_event_query_probe query = {}; > + struct trace_event_call *call = event->tp_event; > + struct trace_uprobe *tu = (struct trace_uprobe *)call->data; > + u64 nmissed, nhit; > + > + if (!capable(CAP_SYS_ADMIN)) > + return -EPERM; > + if (copy_from_user(&query, uquery, sizeof(query))) > + return -EFAULT; > + > + nhit = tu->nhit; > + nmissed = 0; Blindly return 0 is a little weird. Maybe return 0xffffffffffffffff so that the user can tell this is not a valid 0. Or some other idea? Thanks, Song