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UBI (Latin: "where?") manages multiple logical volumes on a single flash device, specifically supporting NAND flash devices. UBI provides a flexible partitioning concept which still allows for wear-levelling across the whole flash device. In a sense, UBI may be compared to the Logical Volume Manager (LVM). Whereas LVM maps logical sector numbers to physical HDD sector numbers, UBI maps logical eraseblocks to physical eraseblocks. More information may be found at http://www.linux-mtd.infradead.org/doc/ubi.html Partitioning/Re-partitioning An UBI volume occupies a certain number of erase blocks. This is limited by a configured maximum volume size, which could also be viewed as the partition size. Each individual UBI volume's size can be changed independently of the other UBI volumes, provided that the sum of all volume sizes doesn't exceed a certain limit. UBI supports dynamic volumes and static volumes. Static volumes are read-only and their contents are protected by CRC check sums. Bad eraseblocks handling UBI transparently handles bad eraseblocks. When a physical eraseblock becomes bad, it is substituted by a good physical eraseblock, and the user does not even notice this. Scrubbing On a NAND flash bit flips can occur on any write operation, sometimes also on read. If bit flips persist on the device, at first they can still be corrected by ECC, but once they accumulate, correction will become impossible. Thus it is best to actively scrub the affected eraseblock, by first copying it to a free eraseblock and then erasing the original. The UBI layer performs this type of scrubbing under the covers, transparently to the UBI volume users. Erase Counts UBI maintains an erase count header per eraseblock. This frees higher-level layers (like file systems) from doing this and allows for centralized erase count management instead. The erase counts are used by the wear-levelling algorithm in the UBI layer. The algorithm itself is exchangeable. Booting from NAND For booting directly from NAND flash the hardware must at least be capable of fetching and executing a small portion of the NAND flash. Some NAND flash controllers have this kind of support. They usually limit the window to a few kilobytes in erase block 0. This "initial program loader" (IPL) must then contain sufficient logic to load and execute the next boot phase. Due to bad eraseblocks, which may be randomly scattered over the flash device, it is problematic to store the "secondary program loader" (SPL) statically. Also, due to bit-flips it may become corrupted over time. UBI allows to solve this problem gracefully by storing the SPL in a small static UBI volume. UBI volumes vs. static partitions UBI volumes are still very similar to static MTD partitions: * both consist of eraseblocks (logical eraseblocks in case of UBI volumes, and physical eraseblocks in case of static partitions; * both support three basic operations - read, write, erase. But UBI volumes have the following advantages over traditional static MTD partitions: * there are no eraseblock wear-leveling constraints in case of UBI volumes, so the user should not care about this; * there are no bit-flips and bad eraseblocks in case of UBI volumes. So, UBI volumes may be considered as flash devices with relaxed restrictions. Where can it be found? Documentation, kernel code and applications can be found in the MTD gits. What are the applications for? The applications help to create binary flash images for two purposes: pfi files (partial flash images) for in-system update of UBI volumes, and plain binary images, with or without OOB data in case of NAND, for a manufacturing step. Furthermore some tools are/and will be created that allow flash content analysis after a system has crashed.. Who did UBI? The original ideas, where UBI is based on, were developed by Andreas Arnez, Frank Haverkamp and Thomas Gleixner. Josh W. Boyer and some others were involved too. The implementation of the kernel layer was done by Artem B. Bityutskiy. The user-space applications and tools were written by Oliver Lohmann with contributions from Frank Haverkamp, Andreas Arnez, and Artem. Joern Engel contributed a patch which modifies JFFS2 so that it can be run on a UBI volume. Thomas Gleixner did modifications to the NAND layer. Alexander Schmidt made some testing work as well as core functionality improvements. Signed-off-by: Artem B. Bityutskiy <dedekind@linutronix.de> Signed-off-by: Frank Haverkamp <haver@vnet.ibm.com>
104 lines
2.7 KiB
Text
104 lines
2.7 KiB
Text
comment "UBI debugging options"
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depends on MTD_UBI
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config MTD_UBI_DEBUG
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bool "UBI debugging"
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depends on SYSFS
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depends on MTD_UBI
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select DEBUG_FS
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select KALLSYMS_ALL
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help
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This option enables UBI debugging.
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config MTD_UBI_DEBUG_MSG
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bool "UBI debugging messages"
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depends on MTD_UBI_DEBUG
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default n
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help
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This option enables UBI debugging messages.
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config MTD_UBI_DEBUG_PARANOID
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bool "Extra self-checks"
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default n
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depends on MTD_UBI_DEBUG
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help
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This option enables extra checks in UBI code. Note this slows UBI down
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significantly.
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config MTD_UBI_DEBUG_DISABLE_BGT
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bool "Do not enable the UBI background thread"
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depends on MTD_UBI_DEBUG
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default n
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help
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This option switches the background thread off by default. The thread
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may be also be enabled/disabled via UBI sysfs.
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config MTD_UBI_DEBUG_USERSPACE_IO
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bool "Direct user-space write/erase support"
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default n
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depends on MTD_UBI_DEBUG
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help
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By default, users cannot directly write and erase individual
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eraseblocks of dynamic volumes, and have to use update operation
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instead. This option enables this capability - it is very useful for
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debugging and testing.
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config MTD_UBI_DEBUG_EMULATE_BITFLIPS
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bool "Emulate flash bit-flips"
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depends on MTD_UBI_DEBUG
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default n
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help
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This option emulates bit-flips with probability 1/50, which in turn
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causes scrubbing. Useful for debugging and stressing UBI.
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config MTD_UBI_DEBUG_EMULATE_WRITE_FAILURES
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bool "Emulate flash write failures"
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depends on MTD_UBI_DEBUG
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default n
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help
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This option emulates write failures with probability 1/100. Useful for
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debugging and testing how UBI handlines errors.
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config MTD_UBI_DEBUG_EMULATE_ERASE_FAILURES
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bool "Emulate flash erase failures"
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depends on MTD_UBI_DEBUG
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default n
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help
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This option emulates erase failures with probability 1/100. Useful for
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debugging and testing how UBI handlines errors.
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menu "Additional UBI debugging messages"
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depends on MTD_UBI_DEBUG
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config MTD_UBI_DEBUG_MSG_BLD
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bool "Additional UBI initialization and build messages"
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default n
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depends on MTD_UBI_DEBUG
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help
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This option enables detailed UBI initialization and device build
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debugging messages.
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config MTD_UBI_DEBUG_MSG_EBA
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bool "Eraseblock association unit messages"
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default n
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depends on MTD_UBI_DEBUG
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help
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This option enables debugging messages from the UBI eraseblock
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association unit.
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config MTD_UBI_DEBUG_MSG_WL
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bool "Wear-leveling unit messages"
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default n
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depends on MTD_UBI_DEBUG
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help
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This option enables debugging messages from the UBI wear-leveling
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unit.
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config MTD_UBI_DEBUG_MSG_IO
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bool "Input/output unit messages"
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default n
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depends on MTD_UBI_DEBUG
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help
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This option enables debugging messages from the UBI input/output unit.
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endmenu # UBI debugging messages
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