The document, at Documentation/admin-guide/pstore-block.rst, tells us how to use pstore/blk and blkoops. Signed-off-by: WeiXiong Liao <liaoweixiong@xxxxxxxxxxxxxxxxx> --- Documentation/admin-guide/pstore-block.rst | 278 +++++++++++++++++++++++++++++ MAINTAINERS | 1 + fs/pstore/Kconfig | 2 + 3 files changed, 281 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 000000000000..58418d429c55 --- /dev/null +++ b/Documentation/admin-guide/pstore-block.rst @@ -0,0 +1,278 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Pstore block oops/panic logger +============================== + +Introduction +------------ + +Pstore block (pstore/blk) is an oops/panic logger that writes its logs to a +block device before the system crashes. It also supports non-block devices such +as mtd device. + +There is a trapper named blkoops for pstore/blk, which makes pstore/blk be +nicer to device drivers. + +Pstore block concepts +--------------------- + +Pstore/blk works as a zone manager as it cuts the block device or partition +into several zones and stores data for different recorders. What device driver +should do is to provide read/write APIs. + +Pstore/blk begins at function ``blkz_register``. Besides, blkoops, a wrapper of +pstore/blk, begins at function ``blkoops_register_blkdev`` for block device and +``blkoops_register_device`` for non-block device, which is recommended instead +of directly using pstore/blk. + +Blkoops provides efficient configuration mothod for pstore/blk, which divides +all configurations of pstore/blk into two parts, configurations for user and +configurations for driver. + +Configurations for user determine how pstore/blk works, such as pmsg_size, +dmesg_size and so on. All of them support both kconfig and module parameters, +but module parameters have priority over kconfig. + +Configurations for driver are all about block/non-block device, such as +total_size of device and read/write operations. Device driver transfers a +structure ``blkoops_device`` defined in *linux/blkoops.h*. + +Configurations for user +----------------------- + +All of these configurations support both kconfig and module parameters, but +module parameters have priority over kconfig. +Here is an example for module parameters:: + + blkoops.blkdev=179:7 blkoops.dmesg_size=64 blkoops.dump_oops=1 + +The detail of each configurations 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 fine to ignore it if you are not block device. + +It accepts the following variants: + +1. <hex_major><hex_minor> device number in hexadecimal represents itself; no + leading 0x, for example b302. +#. /dev/<disk_name> represents the device number of disk +#. /dev/<disk_name><decimal> represents the device number of partition - device + number of disk plus the partition number +#. /dev/<disk_name>p<decimal> - 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=<UUID>/PARTNROFF=<int> to select a partition in relation to a + partition with a known unique id. +#. <major>:<minor> major and minor number of the device separated by a colon. + +dmesg_size +~~~~~~~~~~ + +The chunk size in bytes for dmesg(oops/panic). It **MUST** be a multiple of +4096. If you don't need it, safely set it 0 or ignore it. + +NOTE that, the remaining space, except ``pmsg_size``, ``console_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 there is no more free chunks. + +pmsg_size +~~~~~~~~~ + +The chunk size in bytes for pmsg. It **MUST** be a multiple of 4096. If you +do not need it, safely set it 0 or ignore it. + +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. + +console_size +~~~~~~~~~~~~ + +The chunk size in bytes for console. It **MUST** be a multiple of 4096. If you +do not need it, safely set it 0 or ignore it. + +There is only one chunk for console. + +All log of console will be appended to the chunk. On reboot the contents are +available in /sys/fs/pstore/console-pstore-blk-0. + +ftrace_size +~~~~~~~~~~~ + +The chunk size in bytes for ftrace. It **MUST** be a multiple of 4096. If you +do not need it, safely set it 0 or ignore it. + +There may be several chunks for ftrace, according to how many processors on +your CPU. Each chunk size is equal to (ftrace_size / processors_count). + +All log of ftrace will be appended to the chunk. On reboot the contents are +available in /sys/fs/pstore/ftrace-pstore-blk-[N], where N is the processor +number. + +Persistent function tracing might be useful for debugging software or hardware +related hangs. Here is an example of usage:: + + # mount -t pstore pstore /sys/fs/pstore + # mount -t debugfs debugfs /sys/kernel/debug/ + # echo 1 > /sys/kernel/debug/pstore/record_ftrace + # reboot -f + [...] + # mount -t pstore pstore /sys/fs/pstore + # tail /sys/fs/pstore/ftrace-pstore-blk-0 + CPU:0 ts:109860 c03a4310 c0063ebc cpuidle_select <- cpu_startup_entry+0x1a8/0x1e0 + CPU:0 ts:109861 c03a5878 c03a4324 menu_select <- cpuidle_select+0x24/0x2c + CPU:0 ts:109862 c00670e8 c03a589c pm_qos_request <- menu_select+0x38/0x4cc + CPU:0 ts:109863 c0092bbc c03a5960 tick_nohz_get_sleep_length <- menu_select+0xfc/0x4cc + CPU:0 ts:109865 c004b2f4 c03a59d4 get_iowait_load <- menu_select+0x170/0x4cc + CPU:0 ts:109868 c0063b60 c0063ecc call_cpuidle <- cpu_startup_entry+0x1b8/0x1e0 + CPU:0 ts:109869 c03a433c c0063b94 cpuidle_enter <- call_cpuidle+0x44/0x48 + CPU:0 ts:109871 c03a4000 c03a4350 cpuidle_enter_state <- cpuidle_enter+0x24/0x28 + CPU:0 ts:109873 c0063ba8 c03a4090 sched_idle_set_state <- cpuidle_enter_state+0xa4/0x314 + CPU:0 ts:109874 c03a605c c03a40b4 arm_enter_idle_state <- cpuidle_enter_state+0xc8/0x314 + +dump_oops +~~~~~~~~~ + +Dumping both oopses and panics can be done by setting 1 (not zero) in the +``dump_oops`` member while setting 0 in that variable dumps only the panics. + +Configurations for driver +------------------------- + +Only device driver would care these configurations. Block device driver +refers ``blkoops_register_blkdev`` while ``blkoops_register_device`` for +non-block device. + +The parameters of these two APIs may be of interest to you. + +major +~~~~~ + +It is only requested by block device which is registered by +``blkoops_register_blkdev``. It's the major device number of registered +devices, by which blkoops can get the matching driver for @blkdev. + +total_size +~~~~~~~~~~ + +It is only requested by non-block device which is registered by +``blkoops_register_device``. It tells pstore/blk that the total size +pstore/blk can use. It **MUST** be greater than 4096 and a multiple of 4096. + +If block device, blkoops can get size of block device/partition automatically. + +read/write +~~~~~~~~~~ + +It's generic read/write APIs for pstore/blk, which are requested by non-block +device. The generic APIs are used for almost all data but except panic data, +such as pmsg, console, oops and ftrace. + +The parameter @offset is the relative position of the device. + +Normally the number of bytes read/written should be returned, while for error, +negative number will be returned. The following return numbers mean more: + +-EBUSY: pstore/blk should try again later. + +panic_write (for non-block device) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +It's a interface for panic recorder and will be used only when panic occurs. +Non-block device driver registers it by ``blkoops_register_device``. If panic +log is unnecessary, it's fine to ignore it. + +Note that pstore/blk will recover data from device while mounting pstore +filesystem by default. If panic occurs but pstore/blk does not recover yet, the +first zone of dmesg will be used. + +The parameter @offset is the relative position of the device. + +Normally the number of bytes written should be returned, while for error, +negative number should be returned. + +panic_write (for block device) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +It's much similar to panic_write for non-block device, but panic_write for +block device writes alignment to SECTOR_SIZE, that's why the parameters are +@sects and @start_sect. Block device driver should register it by +``blkoops_register_blkdev``. + +The parameter @start_sect is the relative position of the block device and +partition. If block driver requires absolute position for panic_write, +``blkoops_blkdev_info`` will be helpful, which can provide the absolute +position of the block device (or partition) on the whole disk/flash. + +Normally zero should be returned, otherwise it indicates an error. + +Compression and header +---------------------- + +Block device is large enough for uncompressed dmesg data. Actually we do not +recommend data compression because pstore/blk will insert some information into +the first line of dmesg data. For example:: + + Panic: Total 16 times + +It means that it's the 16th times panic log since the first booting. Sometimes +the oops|panic occurs 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), ``pmsg-pstore-blk-0`` +for pmsg and so on, 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 run 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 require 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. + +Blkoops supports blkoops_blkdev_info(), which is defined in *linux/blkoops.h*, +to get information of block device, such as the device number, sector count and +start sector of the whole disk. diff --git a/MAINTAINERS b/MAINTAINERS index e4ba97130560..a5122e3aaf76 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -13380,6 +13380,7 @@ 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 5649218d2821..24232e96a98a 100644 --- a/fs/pstore/Kconfig +++ b/fs/pstore/Kconfig @@ -162,6 +162,8 @@ 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 -- 1.9.1
