Start working on the "unstable bits" issue to make UBIFS more robust


 * Summary: Start working on the "unstable bits" issue to make UBIFS more robust


 * Proposer: Wolfram Sang

Description
UBIFS on top of UBI is today the defacto standard filesystem for flash-based storage (NOR, NAND) and is already used in many consumer products. It is stable and well tested. There is one major known issue, though, called "unstable bits" (see link in related work), often in accordance with power cuts. The problems involved are complex and even to start tackling them, a concentrated effort is needed. In the description of "unstable bits", there is already a roadmap presented and this proposal suggests to pick up the first task:

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1) Improve the existing power cut emulation infrastructure in UBIFS and start emulating unstable bits. Start with emulating only one type of unstable bits, e.g., type 1.

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When this is in place, it will enable UBIFS developers (and file system developers in general) to do power cut simulations much more easily and fix related bugs or implement proper mechanisms. Automated tests will also benefit from this work.

Given the importance of flash based storage these days, it seems worthwhile to get the ball rolling regarding "unstable bits".

Related work

 * "unstable bits" description - http://www.linux-mtd.infradead.org/doc/ubifs.html#L_unstable_bits

Scope
3 weeks should be needed to make the general emulation proper. If all goes well, maybe more types of power cuts could be implemented in that timeframe.

Contractor Candidates
Artem Bityutskiy (current UBI/UBIFS maintainer) already declined, sadly. But he will be around for reviews etc. Other recently active contributors to MTD/UBI could probably be asked.