Thank you for your correction. I will update the patch in the 12th version.
On 2019/02/28 13:15, Randy Dunlap wrote: > On 2/19/19 3:52 AM, liaoweixiong wrote: >> 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 <liaoweixi...@allwinnertech.com> >> --- >> 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..a828274 >> --- /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 >> block > > to a > block > >> +device before the system crashes. Pstore_blk needs block device driver > > needs the block > >> +registering a partition path of the block device, like /dev/mmcblk0p7 for >> mmc > > to register 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 > > by which a block driver > >> +registers to pstore_blk. Note that, block driver should register to >> pstore_blk > > Note that the block driver should > >> +after block device has registered. Block driver transfers a structure > > The block driver > >> +``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 passing ``read`` and ``write`` in >> blkz_info as > > if you are passing > >> +``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 >> +be saved in ddr buffer. > > what is ddr buffer? > It is a buffer allocated from RAM. I modify it as follow: 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. <hex_major><hex_minor> device number in hexadecimal represents itself no > > 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, that form is used when >> disk > > above; this form > >> + name of partitioned disk ends on a digit. > > 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. >> + >> +See more on section **read/write**. > > in section > >> + >> +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 are safely to set it to 0. > > you can safely > >> + >> +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 > > Pstore_blk > >> +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 > > you can > safely {drop "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, > > It is safe and recommended > >> +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 > > NOTE that the general > >> +self-defined. >> + >> +panic_read/panic_write >> +~~~~~~~~~~~~~~~~~~~~~~ >> + >> +They are ``read/write`` APIs for panic. They are likely to general > > 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 Psotre_blk. > > Pstore_blk. > >> +For example: >> + >> +.. code-block:: c >> + >> + #include <linux/pstore_blk.h> >> + [...] >> + >> + 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 device by ``register_mtd_user``, and get >> the > > devices > >> + matching name MTD partition. >> + >> +NOTE that, all of above are done by block driver rather then pstore_blk. >> You can > > NOTE that all of the above are done by the block driver > >> +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 > > compressing because > >> +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. > > what is "burning"? > It is something about embedded device installing system. It was my negligence not to consider the compatibility of concepts. I modify it as follow: 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 follow line is insert by pstore filesystem. > > following line is inserted > >> +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 > > initializing > >> + 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, no any share resource, you are safely to break >> all > > nor any shared resource; you are safe to break > all > >> + locks. >> +#. Just use cpu to transfer. > > CPU > >> + 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 io map while initialing rather >> than > > Linux I/O initializing > >> + 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 safely to stop and reset them. > > you are safe to > > > > cheers. > -- liaoweixiong