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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 2D5C8C282CA for ; Wed, 13 Feb 2019 14:07:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E82C6222CA for ; Wed, 13 Feb 2019 14:07:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391817AbfBMOHw (ORCPT ); Wed, 13 Feb 2019 09:07:52 -0500 Received: from smtp2207-205.mail.aliyun.com ([121.197.207.205]:51572 "EHLO smtp2207-205.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391685AbfBMOHu (ORCPT ); Wed, 13 Feb 2019 09:07:50 -0500 X-Alimail-AntiSpam: AC=CONTINUE;BC=0.06712966|-1;CH=green;FP=0|0|0|0|0|-1|-1|-1;HT=e02c03311;MF=liaoweixiong@allwinnertech.com;NM=1;PH=DS;RN=16;RT=16;SR=0;TI=SMTPD_---.Dy6iQiS_1550066841; Received: from PC-liaoweixiong.allwinnertech.com(mailfrom:liaoweixiong@allwinnertech.com fp:SMTPD_---.Dy6iQiS_1550066841) by smtp.aliyun-inc.com(10.147.40.233); Wed, 13 Feb 2019 22:07:42 +0800 From: liaoweixiong To: Kees Cook , Anton Vorontsov , Colin Cross , Tony Luck , Jonathan Corbet , Rob Herring , Mark Rutland , liaoweixiong , Mauro Carvalho Chehab , "David S. Miller" , Greg Kroah-Hartman , Nicolas Ferre , Arnd Bergmann Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org Subject: [RFC v8 5/5] Documentation: pstore/blk: create document for pstore_blk Date: Wed, 13 Feb 2019 22:07:08 +0800 Message-Id: <1550066828-18806-6-git-send-email-liaoweixiong@allwinnertech.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1550066828-18806-1-git-send-email-liaoweixiong@allwinnertech.com> References: <1550066828-18806-1-git-send-email-liaoweixiong@allwinnertech.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The document, at Documentation/admin-guide/pstore-block.rst, tells user how to use pstore_blk and the attentions about panic read/write Signed-off-by: liaoweixiong --- Documentation/admin-guide/pstore-block.rst | 227 +++++++++++++++++++++++++++++ MAINTAINERS | 1 + fs/pstore/Kconfig | 4 + 3 files changed, 232 insertions(+) create mode 100644 Documentation/admin-guide/pstore-block.rst diff --git a/Documentation/admin-guide/pstore-block.rst b/Documentation/admin-guide/pstore-block.rst new file mode 100644 index 0000000..4bb8c4c --- /dev/null +++ b/Documentation/admin-guide/pstore-block.rst @@ -0,0 +1,227 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Pstore block oops/panic logger +============================== + +Introduction +------------ + +Pstore block (pstore_blk) is an oops/panic logger that write its logs to block +device before the system crashes. Pstore_blk needs block device driver +registering a partition path of the block device, like /dev/mmcblk0p7 for mmc +driver, and read/write APIs for this partition when on panic. + +Pstore block concepts +--------------------- + +Pstore block begins at function ``blkz_register``, by which block driver +registers to pstore_blk. Recomemd that, block driver should register to +pstore_blk after block device is ready. Block driver transfers a structure +``blkz_info`` which is defined in *linux/pstore_blk.h*. + +The following key members of ``struct blkz_info`` may be of interest to you. + +part_path +~~~~~~~~~ + +The path of partition used for pstore_blk. It may be ``/dev/mmcblk[N]p[M]`` for +mmc, and ``/dev/mtdblock[N]`` for mtd device. + +The ``part_path`` is not necessarily if you self-defined general read/write APIs +on ``blkz_info``. In other words, the ``part_path`` is only used (by function +blkz_default_general_read/write) when general read/write APIs are not defined. + +See more on section **read/write**. + +part_size +~~~~~~~~~ + +The total size in bytes of partition used for pstore_blk. This member **MUST** +be effective and a multiple of 4096. It is recommended to 1M or larger for block +device. + +The block device area is divided into many chunks, and each event writes +a chunk of information. + +dmesg_size +~~~~~~~~~~ + +The chunk size in bytes for dmesg(oops/panic). It **MUST** be a multiple of +SECTOR_SIZE (Most of the time, the SECTOR_SIZE is 512). If you don't need dmesg, +you are safely to set it to 0. + +NOTE that, the remaining space, except ``pmsg_size`` and others, belongs to +dmesg. It means that there are multiple chunks for dmesg. + +Psotre_blk will log to dmesg chunks one by one, and always overwrite the oldest +chunk if no free chunk. + +pmsg_size +~~~~~~~~~ + +The chunk size in bytes for pmsg. It **MUST** be a multiple of SECTOR_SIZE (Most +of the time, the SECTOR_SIZE is 512). If you don't need pmsg, you are safely to +set it to 0. + +There is only one chunk for pmsg. + +Pmsg is a user space accessible pstore object. Writes to */dev/pmsg0* are +appended to the chunk. On reboot the contents are available in +/sys/fs/pstore/pmsg-pstore-blk-0. + +dump_oops +~~~~~~~~~ + +Dumping both oopses and panics can be done by setting 1 in the ``dump_oops`` +member while setting 0 in that variable dumps only the panics. + +read/write +~~~~~~~~~~ + +They are general ``read/write`` APIs. It is safely and recommended to ignore it, +but set ``part_path``. + +These general APIs are used all the time expect panic. The ``read`` API is +usually used to recover data from block device, and the ``write`` API is usually +to flush new data and erase to block device. + +Pstore_blk will temporarily hold all new data before block device is ready. If +you ignore both of ``read/write`` and ``part_path``, the old data will not be +recovered and the new data will not be flushed until panic, using panic APIs. +If you don't have panic APIs neither, all the data will be dropped when reboot. + +NOTE that, the general APIs must check whether the block device is ready if +self-defined. + +panic_read/panic_write +~~~~~~~~~~~~~~~~~~~~~~ + +They are ``read/write`` APIs for panic. They are likely to general +``read/write`` but will be used only when on panic. + +The attentions for panic read/write see section +**Attentions in panic read/write APIs**. + +Register to pstore block +------------------------ + +Block device driver call ``blkz_register`` to register to Psotre_blk. +For example: + +.. code-block:: c + + #include + [...] + + static ssize_t XXXX_panic_read(char *buf, size bytes, loff_t pos) + { + [...] + } + + static ssize_t XXXX_panic_write(const char *buf, size_t bytes, loff_t pos) + { + [...] + } + + struct blkz_info XXXX_info = { + .onwer = THIS_MODULE, + .name = <...>, + .dmesg_size = <...>, + .pmsg_size = <...>, + .dump_oops = true, + .panic_read = XXXX_panic_read, + .panic_write = XXXX_panic_write, + }; + + static int __init XXXX_init(void) + { + [... get partition information ...] + XXXX_info.part_path = <...>; + XXXX_info.part_size = <...>; + + [...] + return blkz_register(&XXXX_info); + } + +There are multiple ways by which you can get partition information. + +A. Use the module parameters and kernel cmdline. +B. Use Device Tree bindings. +C. Use Kconfig. +D. Use Driver Feature. + For example, traverse all MTD device by ``register_mtd_user``, and get the + matching name MTD partition. + +NOTE that, all of above are done by block driver rather then pstore_blk. You can +get sample on blkoops. + +The attentions for panic read/write see section +**Attentions in panic read/write APIs**. + +Compression and header +---------------------- + +Block device is large enough, it is not necessary to compress dmesg data. +Actually, we recommend not compress. Because pstore_blk will insert some +information into the first line of dmesg data if no compression. +For example:: + + Panic: Total 16 times + +It means that it's the 16th times panic log since burning. +Sometimes, the oops|panic counter since burning is very important for embedded +device to judge whether the system is stable. + +The follow line is insert by pstore filesystem. +For example:: + + Oops#2 Part1 + +It means that it's the 2nd times oops log on last booting. + +Reading the data +---------------- + +The dump data can be read from the pstore filesystem. The format for these +files is ``dmesg-pstore-blk-[N]`` for dmesg(oops|panic) and +``pmsg-pstore-blk-0`` for pmsg, where N is the record number. To delete a stored +record from block device, simply unlink the respective pstore file. The +timestamp of the dump file records the trigger time. + +Attentions in panic read/write APIs +----------------------------------- + +If on panic, the kernel is not going to be running for much longer. The tasks +will not be scheduled and the most kernel resources will be out of service. It +looks like a single-threaded program running on a single-core computer. + +The following points need special attention for panic read/write APIs: + +1. Can **NOT** allocate any memory. + + If you need memory, just allocate while the block driver is initialing rather + than waiting until the panic. + +2. Must be polled, **NOT** interrupt driven. + + No task schedule any more. The block driver should delay to ensure the write + succeeds, but NOT sleep. + +3. Can **NOT** take any lock. + + There is no other task, no any share resource, you are safely to break all + locks. + +4. Just use cpu to transfer. + + Do not use DMA to transfer unless you are sure that DMA will not keep lock. + +5. Operate register directly. + + Try not to use linux kernel resources. Do io map while initialing rather than + waiting until the panic. + +6. Reset your block device and controller if necessary. + + If you are not sure the state of you block device and controller when panic, + you are safely to stop and reset them. diff --git a/MAINTAINERS b/MAINTAINERS index 44647a8..4dd95d3 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -12317,6 +12317,7 @@ F: include/linux/pstore* F: drivers/firmware/efi/efi-pstore.c F: drivers/acpi/apei/erst.c F: Documentation/admin-guide/ramoops.rst +F: Documentation/admin-guide/pstore-block.rst F: Documentation/devicetree/bindings/reserved-memory/ramoops.txt F: Documentation/devicetree/bindings/pstore-block/ K: \b(pstore|ramoops|blkoops) diff --git a/fs/pstore/Kconfig b/fs/pstore/Kconfig index f0a1a49..c32f66c 100644 --- a/fs/pstore/Kconfig +++ b/fs/pstore/Kconfig @@ -160,6 +160,10 @@ config PSTORE_BLK This enables panic and oops message to be logged to a block dev where it can be read back at some later point. + For more information, see Documentation/admin-guide/pstore-block.rst. + + If unsure, say N. + config PSTORE_BLKOOPS tristate "pstore block with oops logger" depends on PSTORE_BLK -- 1.9.1