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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1D4B2C74A5B for ; Fri, 24 Mar 2023 00:06:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230021AbjCXAGU (ORCPT ); Thu, 23 Mar 2023 20:06:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45928 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229660AbjCXAGT (ORCPT ); Thu, 23 Mar 2023 20:06:19 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7177E2C67A; Thu, 23 Mar 2023 17:06:13 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 0C79F6291C; Fri, 24 Mar 2023 00:06:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 92FE5C433EF; Fri, 24 Mar 2023 00:06:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1679616372; bh=6YUc1zE9iK43mYE5/UeWdUVHzImsi2aOIpYBXQrJjDU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=MzgTS3rbgGiXsaj2bd+tc7xbUt4xpNQcv1YNh1U3m+jH30qbR0EvZm+hoUf5YBVaA 7MIacQfAn2+WjP6Gp97Lgk1nZQc3FbJimw2CfvSwXiuQeKzZ8s+HJD0Poj69oF96oO VgefjAHwu7MceSfe+c/g0V8+/+R379WaYZwOBmb9U+Z2JALZcStIvN8LhdDS6qGiND ZNKwTemAs4WlnXbyO+k41YZmQ8AfPaLcVjI8DyDj0z1xuI52Vi6UM60n+wbPSwgixG swyYdu077FL5Fpis1fAFiiZAJFCxgLntNIvaiFo6+0GfM3c2lPB4M73ibC51cug2Xz eBuSTZOX/BXJA== Date: Fri, 24 Mar 2023 08:06:07 +0800 From: Masami Hiramatsu (Google) To: Beau Belgrave Cc: rostedt@goodmis.org, mathieu.desnoyers@efficios.com, dcook@linux.microsoft.com, alanau@linux.microsoft.com, brauner@kernel.org, akpm@linux-foundation.org, ebiederm@xmission.com, keescook@chromium.org, tglx@linutronix.de, linux-trace-devel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v8 09/11] tracing/user_events: Update documentation for ABI Message-Id: <20230324080607.37bf83f86ac9bfcaee675d95@kernel.org> In-Reply-To: <20230221211143.574-10-beaub@linux.microsoft.com> References: <20230221211143.574-1-beaub@linux.microsoft.com> <20230221211143.574-10-beaub@linux.microsoft.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-trace-devel@vger.kernel.org Hi Beau, On Tue, 21 Feb 2023 13:11:41 -0800 Beau Belgrave wrote: > The ABI for user_events has changed from mmap() based to remote writes. > Update the documentation to reflect these changes, add new section for > unregistering events since lifetime is now tied to tasks instead of > files. Thanks for updating the document. This is good. And I would like to ask you to update one more thing in the document. In "the Writing Data" Section, ----- For example, if I have a struct like this:: struct payload { int src; int dst; int flags; }; ----- This payload has to be packed too. This may be a split patch as a fix because it is not related to this series. Thank you, > > Signed-off-by: Beau Belgrave > --- > Documentation/trace/user_events.rst | 177 ++++++++++++++++------------ > 1 file changed, 102 insertions(+), 75 deletions(-) > > diff --git a/Documentation/trace/user_events.rst b/Documentation/trace/user_events.rst > index 9f181f342a70..0180714f10e3 100644 > --- a/Documentation/trace/user_events.rst > +++ b/Documentation/trace/user_events.rst > @@ -11,20 +11,19 @@ that can be viewed via existing tools, such as ftrace and perf. > To enable this feature, build your kernel with CONFIG_USER_EVENTS=y. > > Programs can view status of the events via > -/sys/kernel/debug/tracing/user_events_status and can both register and write > -data out via /sys/kernel/debug/tracing/user_events_data. > +/sys/kernel/tracing/user_events_status and can both register and write > +data out via /sys/kernel/tracing/user_events_data. > > -Programs can also use /sys/kernel/debug/tracing/dynamic_events to register and > +Programs can also use /sys/kernel/tracing/dynamic_events to register and > delete user based events via the u: prefix. The format of the command to > dynamic_events is the same as the ioctl with the u: prefix applied. > > Typically programs will register a set of events that they wish to expose to > tools that can read trace_events (such as ftrace and perf). The registration > -process gives back two ints to the program for each event. The first int is > -the status bit. This describes which bit in little-endian format in the > -/sys/kernel/debug/tracing/user_events_status file represents this event. The > -second int is the write index which describes the data when a write() or > -writev() is called on the /sys/kernel/debug/tracing/user_events_data file. > +process tells the kernel which address and bit to reflect if any tool has > +enabled the event and data should be written. The registration will give back > +a write index which describes the data when a write() or writev() is called > +on the /sys/kernel/tracing/user_events_data file. > > The structures referenced in this document are contained within the > /include/uapi/linux/user_events.h file in the source tree. > @@ -35,29 +34,70 @@ filesystem and may be mounted at different paths than above.* > Registering > ----------- > Registering within a user process is done via ioctl() out to the > -/sys/kernel/debug/tracing/user_events_data file. The command to issue is > +/sys/kernel/tracing/user_events_data file. The command to issue is > DIAG_IOCSREG. > > This command takes a packed struct user_reg as an argument:: > > struct user_reg { > - u32 size; > - u64 name_args; > - u32 status_bit; > - u32 write_index; > - }; > + /* Input: Size of the user_reg structure being used */ > + __u32 size; > + > + /* Input: Bit in enable address to use */ > + __u8 enable_bit; > + > + /* Input: Enable size in bytes at address */ > + __u8 enable_size; > + > + /* Input: Flags for future use, set to 0 */ > + __u16 flags; > + > + /* Input: Address to update when enabled */ > + __u64 enable_addr; > + > + /* Input: Pointer to string with event name, description and flags */ > + __u64 name_args; > + > + /* Output: Index of the event to use when writing data */ > + __u32 write_index; > + } __attribute__((__packed__)); > + > +The struct user_reg requires all the above inputs to be set appropriately. > > -The struct user_reg requires two inputs, the first is the size of the structure > -to ensure forward and backward compatibility. The second is the command string > -to issue for registering. Upon success two outputs are set, the status bit > -and the write index. > ++ size: This must be set to sizeof(struct user_reg). > + > ++ enable_bit: The bit to reflect the event status at the address specified by > + enable_addr. > + > ++ enable_size: The size of the value specified by enable_addr. > + This must be 4 (32-bit) or 8 (64-bit). 64-bit values are only allowed to be > + used on 64-bit kernels, however, 32-bit can be used on all kernels. > + > ++ flags: The flags to use, if any. For the initial version this must be 0. > + Callers should first attempt to use flags and retry without flags to ensure > + support for lower versions of the kernel. If a flag is not supported -EINVAL > + is returned. > + > ++ enable_addr: The address of the value to use to reflect event status. This > + must be naturally aligned and write accessible within the user program. > + > ++ name_args: The name and arguments to describe the event, see command format > + for details. > + > +Upon successful registration the following is set. > + > ++ write_index: The index to use for this file descriptor that represents this > + event when writing out data. The index is unique to this instance of the file > + descriptor that was used for the registration. See writing data for details. > > User based events show up under tracefs like any other event under the > subsystem named "user_events". This means tools that wish to attach to the > -events need to use /sys/kernel/debug/tracing/events/user_events/[name]/enable > +events need to use /sys/kernel/tracing/events/user_events/[name]/enable > or perf record -e user_events:[name] when attaching/recording. > > -**NOTE:** *The write_index returned is only valid for the FD that was used* > +**NOTE:** The event subsystem name by default is "user_events". Callers should > +not assume it will always be "user_events". Operators reserve the right in the > +future to change the subsystem name per-process to accomodate event isolation. > > Command Format > ^^^^^^^^^^^^^^ > @@ -94,9 +134,9 @@ Would be represented by the following field:: > struct mytype myname 20 > > Deleting > ------------ > +-------- > Deleting an event from within a user process is done via ioctl() out to the > -/sys/kernel/debug/tracing/user_events_data file. The command to issue is > +/sys/kernel/tracing/user_events_data file. The command to issue is > DIAG_IOCSDEL. > > This command only requires a single string specifying the event to delete by > @@ -104,92 +144,79 @@ its name. Delete will only succeed if there are no references left to the > event (in both user and kernel space). User programs should use a separate file > to request deletes than the one used for registration due to this. > > -Status > ------- > -When tools attach/record user based events the status of the event is updated > -in realtime. This allows user programs to only incur the cost of the write() or > -writev() calls when something is actively attached to the event. > - > -User programs call mmap() on /sys/kernel/debug/tracing/user_events_status to > -check the status for each event that is registered. The bit to check in the > -file is given back after the register ioctl() via user_reg.status_bit. The bit > -is always in little-endian format. Programs can check if the bit is set either > -using a byte-wise index with a mask or a long-wise index with a little-endian > -mask. > - > -Currently the size of user_events_status is a single page, however, custom > -kernel configurations can change this size to allow more user based events. In > -all cases the size of the file is a multiple of a page size. > +Unregistering > +------------- > +If after registering an event it is no longer wanted to be updated then it can > +be disabled via ioctl() out to the /sys/kernel/tracing/user_events_data file. > +The command to issue is DIAG_IOCSUNREG. This is different than deleting, where > +deleting actually removes the event from the system. Unregistering simply tells > +the kernel your process is no longer interested in updates to the event. > > -For example, if the register ioctl() gives back a status_bit of 3 you would > -check byte 0 (3 / 8) of the returned mmap data and then AND the result with 8 > -(1 << (3 % 8)) to see if anything is attached to that event. > +This command takes a packed struct user_unreg as an argument:: > > -A byte-wise index check is performed as follows:: > + struct user_unreg { > + /* Input: Size of the user_unreg structure being used */ > + __u32 size; > > - int index, mask; > - char *status_page; > + /* Input: Bit to unregister */ > + __u8 disable_bit; > > - index = status_bit / 8; > - mask = 1 << (status_bit % 8); > + /* Input: Reserved, set to 0 */ > + __u8 __reserved; > > - ... > + /* Input: Reserved, set to 0 */ > + __u16 __reserved2; > > - if (status_page[index] & mask) { > - /* Enabled */ > - } > + /* Input: Address to unregister */ > + __u64 disable_addr; > + } __attribute__((__packed__)); > > -A long-wise index check is performed as follows:: > +The struct user_unreg requires all the above inputs to be set appropriately. > > - #include > - #include > ++ size: This must be set to sizeof(struct user_unreg). > > - #if __BITS_PER_LONG == 64 > - #define endian_swap(x) htole64(x) > - #else > - #define endian_swap(x) htole32(x) > - #endif > ++ disable_bit: This must be set to the bit to disable (same bit that was > + previously registered via enable_bit). > > - long index, mask, *status_page; > ++ disable_addr: This must be set to the address to disable (same address that was > + previously registered via enable_addr). > > - index = status_bit / __BITS_PER_LONG; > - mask = 1L << (status_bit % __BITS_PER_LONG); > - mask = endian_swap(mask); > +**NOTE:** Events are automatically unregistered when execve() is invoked. During > +fork() the registered events will be retained and must be unregistered manually > +in each process if wanted. > > - ... > +Status > +------ > +When tools attach/record user based events the status of the event is updated > +in realtime. This allows user programs to only incur the cost of the write() or > +writev() calls when something is actively attached to the event. > > - if (status_page[index] & mask) { > - /* Enabled */ > - } > +The kernel will update the specified bit that was registered for the event as > +tools attach/detach from the event. User programs simply check if the bit is set > +to see if something is attached or not. > > Administrators can easily check the status of all registered events by reading > the user_events_status file directly via a terminal. The output is as follows:: > > - Byte:Name [# Comments] > + Name [# Comments] > ... > > Active: ActiveCount > Busy: BusyCount > - Max: MaxCount > > For example, on a system that has a single event the output looks like this:: > > - 1:test > + test > > Active: 1 > Busy: 0 > - Max: 32768 > > If a user enables the user event via ftrace, the output would change to this:: > > - 1:test # Used by ftrace > + test # Used by ftrace > > Active: 1 > Busy: 1 > - Max: 32768 > - > -**NOTE:** *A status bit of 0 will never be returned. This allows user programs > -to have a bit that can be used on error cases.* > > Writing Data > ------------ > -- > 2.25.1 > -- Masami Hiramatsu (Google)