From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-f74.google.com (mail-ej1-f74.google.com [209.85.218.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 36F6D3446A5 for ; Thu, 19 Feb 2026 15:03:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771513420; cv=none; b=SXbpRnHgvR2CCI3IaFf0cLAFYiSGtLDubyH5j65p5zwCU6UqbmkiA36uQ0K8P1iTrt+jurqvLCLOiR+vyPPpqOc49QKPTZiuYIrEdK6NL/+iB675nmF0fF2VYzCFXkYC4SvcPtyK89zk+bnJyQBiSbP7kEQ8/Z5Q1zjrctwg0GQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771513420; c=relaxed/simple; bh=I+pJGIs0Epojic7l7vjIxFwm13eg3s/jxJWStIzBqmU=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=oJEW9rL8hPunsI1SSo+ZQXkkl1XG/5EbONW5Z+IcCUjICBVy7ZqyY+Vm4pR5CEgACFF+p3o4el3ErjIVBeIi7KBMFUXlaKvvl6SCov8wo5Yv844eIe01IOLa8TPJaf3tBK7mtfa2cCaQGGMpymnp1Fy9hzJLoWZ5T7zYORJn/EQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=N95R+zz2; arc=none smtp.client-ip=209.85.218.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="N95R+zz2" Received: by mail-ej1-f74.google.com with SMTP id a640c23a62f3a-b8fa71b83a0so112584366b.2 for ; Thu, 19 Feb 2026 07:03:39 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1771513418; x=1772118218; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=sPhLrsaL6GHqnFz8k7XCh7wMYB+F4ptERk94umByGuM=; b=N95R+zz2YdPXGKFcOXK6XGyaZrPBiHzCxG4lndIxtpceyuvZWCNqy5Ku5KUi7sg5ZQ SqqAn8XvZ18RprFQN/qj37iAc1xY/Cn/EccKn/NCFlVmI5JuhSj+HRkCV2RY1wcX8rG0 +JdgBU/KBkKRXkTLDLTzEjWYSjfP308SC4QccW6yOJ6KFxEQBMedoVxF+0AN2IO40+0t IvOR2COgiwMvAySYx6970gSs2CYYlocGc2qPCOnOV4j29WjLfbFWPcA5O775LffbRru7 5rWFq13d/+fQvvi5nSFOyUKc2PEB11qruJnka66X81sDMtKfVxEIiCvBPJxRir6jQi3Z 3Vgg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1771513418; x=1772118218; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=sPhLrsaL6GHqnFz8k7XCh7wMYB+F4ptERk94umByGuM=; b=XlHG6EcMR1/nWh1zCPfD65UknOyXZqLtGsaFbYfubx/nPIOOFv8clTAuSqIXJ5jKT3 0XzxwwI4upK69C/1qgMPcCOXpeg6F0rtEz/eL/Z/G7ve+yGvQcRtFfZXx1PvuYuo8tAW 81s2Vrpt7H+6gxsRH62fErLKmHKcjxegZ85T3KvhkKIf9tcjoxmNi+BXOQUb7waoWEIA 1bGg6+fFK5GcDnFnxEc6hWdwQqHuIepzh3OaiXqoeTZJyYC8eoWgwN8ekrsVA/gtluzV XFc1Q5ZB/o+McJAg79pe0pvNr3G4SouS1Zox65umGKGMdAhLws5eJpOdDxjAO908mHmV KELw== X-Forwarded-Encrypted: i=1; AJvYcCWPeNrUSd+7lLdM3E6iYLBN5LGJAsuvJkxlMiRaSvuPZaj/AS27jk9tQWfrDKhSba8+TVpw8LT11CsMdDFMK2udAi8=@vger.kernel.org X-Gm-Message-State: AOJu0YzFbEEPa5761bLQPRC7gnkMx1Kk1j+4iOhoumbuMBCsjJ+qx18X SGt6oDsVnhpxpl3yCpqnlLJS6XNy8g70OvOwk6JrZHVFJJw76MLLtE9nLQl2ANLYNWeIsS/CUgy MTyx3qL+mY/Zu2jnu+WnXHw== X-Received: from ejcyl14.prod.google.com ([2002:a17:907:bc8e:b0:b8f:943e:13b9]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a17:907:1c82:b0:b88:16dd:d835 with SMTP id a640c23a62f3a-b903da49047mr298923766b.1.1771513417420; Thu, 19 Feb 2026 07:03:37 -0800 (PST) Date: Thu, 19 Feb 2026 15:02:53 +0000 In-Reply-To: <20260219150307.14538-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260219150307.14538-1-vdonnefort@google.com> X-Mailer: git-send-email 2.53.0.335.g19a08e0c02-goog Message-ID: <20260219150307.14538-17-vdonnefort@google.com> Subject: [PATCH v12 16/30] Documentation: tracing: Add tracing remotes From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, linux-trace-kernel@vger.kernel.org, maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, jstultz@google.com, qperret@google.com, will@kernel.org, aneesh.kumar@kernel.org, kernel-team@android.com, linux-kernel@vger.kernel.org, Vincent Donnefort Content-Type: text/plain; charset="UTF-8" Add documentation about the newly introduced tracing remotes framework. Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst index 338bc4d7cfab..036db96864d2 100644 --- a/Documentation/trace/index.rst +++ b/Documentation/trace/index.rst @@ -91,6 +91,17 @@ interactions. user_events uprobetracer +Remote Tracing +-------------- + +This section covers the framework to read compatible ring-buffers, written by +entities outside of the kernel (most likely firmware or hypervisor) + +.. toctree:: + :maxdepth: 1 + + remotes + Additional Resources -------------------- diff --git a/Documentation/trace/remotes.rst b/Documentation/trace/remotes.rst new file mode 100644 index 000000000000..1f9d764f69aa --- /dev/null +++ b/Documentation/trace/remotes.rst @@ -0,0 +1,66 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============== +Tracing Remotes +=============== + +:Author: Vincent Donnefort + +Overview +======== +Firmware and hypervisors are black boxes to the kernel. Having a way to see what +they are doing can be useful to debug both. This is where remote tracing buffers +come in. A remote tracing buffer is a ring buffer executed by the firmware or +hypervisor into memory that is memory mapped to the host kernel. This is similar +to how user space memory maps the kernel ring buffer but in this case the kernel +is acting like user space and the firmware or hypervisor is the "kernel" side. +With a trace remote ring buffer, the firmware and hypervisor can record events +for which the host kernel can see and expose to user space. + +Register a remote +================= +A remote must provide a set of callbacks `struct trace_remote_callbacks` whom +description can be found below. Those callbacks allows Tracefs to enable and +disable tracing and events, to load and unload a tracing buffer (a set of +ring-buffers) and to swap a reader page with the head page, which enables +consuming reading. + +.. kernel-doc:: include/linux/trace_remote.h + +Once registered, an instance will appear for this remote in the Tracefs +directory **remotes/**. Buffers can then be read using the usual Tracefs files +**trace_pipe** and **trace**. + +Declare a remote event +====================== +Macros are provided to ease the declaration of remote events, in a similar +fashion to in-kernel events. A declaration must provide an ID, a description of +the event arguments and how to print the event: + +.. code-block:: c + + REMOTE_EVENT(foo, EVENT_FOO_ID, + RE_STRUCT( + re_field(u64, bar) + ), + RE_PRINTK("bar=%lld", __entry->bar) + ); + +Then those events must be declared in a C file with the following: + +.. code-block:: c + + #define REMOTE_EVENT_INCLUDE_FILE foo_events.h + #include + +This will provide a `struct remote_event remote_event_foo` that can be given to +`trace_remote_register`. + +Registered events appear in the remote directory under **events/**. + +Simple ring-buffer +================== +A simple implementation for a ring-buffer writer can be found in +kernel/trace/simple_ring_buffer.c. + +.. kernel-doc:: include/linux/simple_ring_buffer.h -- 2.53.0.335.g19a08e0c02-goog