From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.0 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,UNPARSEABLE_RELAY autolearn=unavailable autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 2A5CC7D08A for ; Tue, 19 Mar 2019 15:45:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727810AbfCSPpV (ORCPT ); Tue, 19 Mar 2019 11:45:21 -0400 Received: from smtp2207-205.mail.aliyun.com ([121.197.207.205]:56924 "EHLO smtp2207-205.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727081AbfCSPpS (ORCPT ); Tue, 19 Mar 2019 11:45:18 -0400 X-Alimail-AntiSpam: AC=CONTINUE;BC=0.07436282|-1;CH=green;DM=CONTINUE|CONTINUE|true|0.090024-0.059972-0.850004;FP=0|0|0|0|0|-1|-1|-1;HT=e01l01425;MF=liaoweixiong@allwinnertech.com;NM=1;PH=DS;RN=16;RT=16;SR=0;TI=SMTPD_---.EA6pZCu_1553010300; Received: from PC-liaoweixiong.allwinnertech.com(mailfrom:liaoweixiong@allwinnertech.com fp:SMTPD_---.EA6pZCu_1553010300) by smtp.aliyun-inc.com(10.147.41.121); Tue, 19 Mar 2019 23:45:12 +0800 From: liaoweixiong To: Kees Cook , Anton Vorontsov , Colin Cross , Tony Luck , Jonathan Corbet , Mauro Carvalho Chehab , "David S. Miller" , Greg Kroah-Hartman , Nicolas Ferre , Arnd Bergmann , Rob Herring , Randy Dunlap , "Paul E. McKenney" Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, liaoweixiong Subject: [PATCH v14 4/4] Documentation: pstore/blk: create document for pstore_blk Date: Tue, 19 Mar 2019 23:45:52 +0800 Message-Id: <1553010352-13040-5-git-send-email-liaoweixiong@allwinnertech.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1553010352-13040-1-git-send-email-liaoweixiong@allwinnertech.com> References: <1553010352-13040-1-git-send-email-liaoweixiong@allwinnertech.com> Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@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 | 233 +++++++++++++++++++++++++++++ MAINTAINERS | 1 + fs/pstore/Kconfig | 4 + 3 files changed, 238 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..c22245d --- /dev/null +++ b/Documentation/admin-guide/pstore-block.rst @@ -0,0 +1,233 @@ +.. 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 a block +device before the system crashes. Pstore_blk needs the block device driver +to register a partition 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 a block driver +registers to pstore_blk. Note that the block driver should register to +pstore_blk after block device has registered. The 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. + +blkdev +~~~~~~ + +The block device to use. Most of the time, it is a partition of block device. +It's ok to keep it as NULL if you are passing ``read`` and ``write`` in +blkz_info as ``blkdev`` is used by blkz_default_general_read/write. If both of +``blkdev``, ``read`` and ``write`` are NULL, no block device is effective and +the data will only be saved in RAM. + +It accept the following variants: + +1. device number in hexadecimal represents itself; no + leading 0x, for example b302. +#. /dev/ represents the device number of disk +#. /dev/ represents the device number of partition - device + number of disk plus the partition number +#. /dev/p - same as the above; this form is used when disk + name of partitioned disk ends with a digit. +#. PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF representing the unique id of + a partition if the partition table provides it. The UUID may be either an + EFI/GPT UUID, or refer to an MSDOS partition using the format SSSSSSSS-PP, + where SSSSSSSS is a zero-filled hex representation of the 32-bit + "NT disk signature", and PP is a zero-filled hex representation of the + 1-based partition number. +#. PARTUUID=/PARTNROFF= to select a partition in relation to a + partition with a known unique id. +#. : major and minor number of the device separated by a colon. + +See more in section **read/write**. + +total_size +~~~~~~~~~~ + +The total size in bytes of block device used for pstore_blk. It **MUST** be less +than or equal to size of block device if ``blkdev`` valid. It **MUST** be a +multiple of 4096. If ``total_size`` is zero with ``blkdev``, ``total_size`` will be +set to equal to size of ``blkdev``. + +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 can 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. + +Pstore_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 can safely 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 safe and recommended to ignore it, +but set ``blkdev``. + +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 ``blkdev``, the old data will be lost. + +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 like the 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 Pstore_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 block device information ...] + XXXX_info.blkdev = <...>; + XXXX_info.total_size = <...>; + + [...] + return blkz_register(&XXXX_info); + } + +There are multiple ways by which you can get block device 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 devices by ``register_mtd_user``, and get the + matching name MTD partition. + +NOTE that all of the above are done by the 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 compressing 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 the first booting. +Sometimes, the oops|panic counter since burning is very important for embedded +device to judge whether the system is stable. + +The following line is inserted 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 initializing + rather than waiting until the panic. +#. Must be polled, **NOT** interrupt driven. + No task schedule any more. The block driver should delay to ensure the write + succeeds, but NOT sleep. +#. Can **NOT** take any lock. + There is no other task, nor any share resource; you are safe to break all + locks. +#. Just use CPU to transfer. + Do not use DMA to transfer unless you are sure that DMA will not keep lock. +#. Operate register directly. + Try not to use Linux kernel resources. Do I/O map while initializing rather + than waiting until the panic. +#. 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 safe to stop and reset them. diff --git a/MAINTAINERS b/MAINTAINERS index 4e9242a..9ddca0e 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 K: \b(pstore|ramoops|blkoops) diff --git a/fs/pstore/Kconfig b/fs/pstore/Kconfig index 62d4cda..e6845eb 100644 --- a/fs/pstore/Kconfig +++ b/fs/pstore/Kconfig @@ -161,6 +161,10 @@ 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