From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) (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 2995047F2F1 for ; Wed, 12 Aug 2026 16:14:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.71 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786551247; cv=none; b=C5/7QipYFgA7pKTejxbzl8g70H/y7CRIONUv8OdAgje1NWqz/89wfYHRx0znh3uMcgCHTNDpCKp3Fr2zYSYB6mqDK5iiz2DSgTobnVWz10RVy6HtTyf2jphKXj4nQKyKc+B+gWAzSwjbhnBDZ62MnzUILB1T9roVXbUVrYB+yXo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786551247; c=relaxed/simple; bh=hnNTw2qatm79qODsgszSWfdN03d3G9Z8ONnvzCmX05A=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=mc8jj90yDgGzj00vC2zdQpnaUJp/lVojRSUvgplasFRIbbrX3NTKaJEVQdftWqzQEdjhus04y/VTrWh51M7R8jB9AdYMy2XIp6flAiDITI0gr4+8L+UFQ/CplznouGaKtNKIj1S+uOD2J5B/Gu+V0Y9my5nuXwud9bTfWrXRziI= 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=TcJQwVN2; arc=none smtp.client-ip=209.85.128.71 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="TcJQwVN2" Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-4997d718093so5129185e9.0 for ; Wed, 12 Aug 2026 09:14:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1786551243; x=1787156043; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=Xf3GDEXCOTi5YGLrqENHCx6PSENZcg+BQDjs7+C49go=; b=TcJQwVN28nnyOWInaZ1jE9CHDJKNFCoXs3ZNOe4g+3itPE019jUECwGoTWX4oOKo5p NAabOWXDrOARH9WtnVpVYFKefvPslya57/QV7BmwTDlNtAnoQrT7Nc8idsJyE+agZIJ6 V2f4kIQh3XHqYfxIsGJvMH6WCdI3iHCNuCDp5aP2TXVbtPUiDt23cBOw/1Z0qO0608ML hySBt1/jyA/OXJqB3YHWMpoMYOD10dewp9ihjtEUcDxnIwx18jCDTxXzZHXqJ494Rx7X IG3slBaXCEtrWAEaYCfPA7Kol5gIxE8yRrddII3HFQ/+8wWIFW63MyICWoG+S+54dp+d kGLg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786551243; x=1787156043; h=content-type: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:content-type; bh=Xf3GDEXCOTi5YGLrqENHCx6PSENZcg+BQDjs7+C49go=; b=A9VhHUR0r2MWzvbs+fFJQKA1rm4mEgLH7vmK+PqAA6g41sLgSCRYsCkQuxYZ7kTOqo 5V01mTEGsQBPU8ZiqePVAwjvWjG7rR7SKmWzF4YWiB8F9ZsogN66Nj79TfmnNDyRdYYM VmtL+yFl/IyFgFn1cDkOJmm5PVAJGmKpmJjtROGWGMW/qw+Av+J+VDRACiAiXzOJfZVX cxkg9AyF/aj+Sat6+jsYe5tdli2qIztN3lEzns/qmf4U20JkJTnIvrcNam5Are8y94Ad gelYS3xTLDCSly4lBD2MYNMScP7zpmfhH2HYyRnMBUoc5gZPS03OATm7ovwVjgFA75kh GoEw== X-Forwarded-Encrypted: i=1; AHgh+Rpvz9rSxmqYCKWFOlN+KizcQ19q83Y1g3GMWPrInd4Y1hz7unY7di+5CyZYYAAhDctg6y645+EUENdUhFK3K6Sgu6M=@vger.kernel.org X-Gm-Message-State: AOJu0YyfqYQ082HO0xHIKvUfb8+90zOoVtGCe2nHXpvnnQ9jSEVQ7zJl 6rndRG01qRVO03nUxv7rNa7BUoNNcadEG6OAZlm4HBem/ZixsSpTALJCDATTLBAOZRoz7P+JXuI 2VUD0JL5VIJ4ph41M/NQbSA== X-Received: from wmqy6.prod.google.com ([2002:a05:600c:3646:b0:493:d1b8:3df5]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:468f:b0:499:4892:e84e with SMTP id 5b1f17b1804b1-4997c14569amr67469745e9.11.1786551243305; Wed, 12 Aug 2026 09:14:03 -0700 (PDT) Date: Wed, 12 Aug 2026 17:13:39 +0100 In-Reply-To: <20260812161340.2417322-1-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: <20260812161340.2417322-1-vdonnefort@google.com> X-Mailer: git-send-email 2.55.0.691.gc56d675ccc-goog Message-ID: <20260812161340.2417322-18-vdonnefort@google.com> Subject: [PATCH v5 17/18] Documentation: tracing/remotes: Add detailed tracefs layout From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org Cc: mathieu.desnoyers@efficios.com, kernel-team@android.com, linux-kernel@vger.kernel.org, Vincent Donnefort Content-Type: text/plain; charset="UTF-8" Add a description for each tracefs file available in a trace remote instance. Signed-off-by: Vincent Donnefort diff --git a/Documentation/trace/remotes.rst b/Documentation/trace/remotes.rst index 1f9d764f69aa..b02ebed4a03f 100644 --- a/Documentation/trace/remotes.rst +++ b/Documentation/trace/remotes.rst @@ -19,8 +19,8 @@ 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 +A remote must provide a set of callbacks `struct trace_remote_callbacks` whose +description can be found below. Those callbacks allow 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. @@ -28,8 +28,66 @@ 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**. +directory **remotes/**. The files within this directory allow configuring +and reading the remote buffer (see `The File System` below). + +The File System +=============== +A remote tracing instance is represented by a directory in Tracefs under +**remotes/**. The layout and files within it are very similar to standard ftrace +instances. Inside the remote directory, the following files and directories are +available: + + tracing_on + This file allows enabling or disabling the remote tracing. + + buffer_size_kb + This file displays and allows changing the size of the per-CPU ring + buffers used by the remote. It also shows if the buffer is **loaded** or + **unloaded**. To change the size, the remote buffers must be unloaded + first. Remote buffers are automatically unloaded when **tracing_on** is + off, no one is reading the buffer (either by accessing **trace_pipe** or + when **dmesg** is on) and no events remain in the buffer. + + trace + Display the human-readable content of the remote buffers. Reading this + file is non-consuming. Writing to this file clears the ring buffers. + + trace_pipe + Similar to **trace** but reading it consumes the events from the ring + buffers (consuming read). It blocks if there are no new events. + + dmesg + When enabled, all events from the remote are redirected to the kernel + dmesg. This is similar to the **tp_printk** option for in-kernel events. + It counts as a reader of the remote buffers and prevents unloading. + + dump_on_panic + When enabled, the remote tracing buffer is dumped to the console when a + kernel panic occurs. + + poll_ms + Modifies the polling interval for the trace_remote. + + per_cpu/ + This directory contains subdirectories for each possible CPU (e.g., + **cpu0/**, **cpu1/** ...) + + per_cpu/cpuX/trace + This is similar to the **trace** file, but it will only display the data + specific for the CPU. If written to, it only clears the specific CPU + buffer. + + per_cpu/cpuX/trace_pipe + This is similar to the **trace_pipe** file, and is a consuming read, but + it will only display (and consume) the data specific to the CPU. + + events/ + This directory contains remote events that can be enabled or disabled. + + events/enable + Allows enabling or disabling all the remote events. + Declare a remote event ====================== -- 2.55.0.691.gc56d675ccc-goog