On Tuesday 22 April 2003 21:18, liuke(??) wrote:
> hello everyone!
> Would you tell me how yaffs and jffs(2) realize their jounals? Just
> simply by copying pages or nodes? Are there journal files on disk? thank u
There is a doc on this in the CVS that covers this briefly.
Basically, what journaling means in this context is that we update files by
writing "patch records" to NAND. THus, we never change the file structure so
the file can never be in a state which is unrecoverable.
YAFFS takes this to the extreme. All data in files is in the form of a data
pages, tagged with the file id and the position of the data in the file. Thus
we overwrite a section of a file by writing new pages to NAND and discarding
the old ones for subsequent garbage collection.
When the file system is re-mounted we read all the tags and reconstruct the
file structure in trees in RAM. Thus, there is no on-disk file structure data
to get corrupted.
YAFFS is therefore very robust.
-- CHarles
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