3 Jun 14:46
JFFS2 - BBC - model file support
Ferenc Havasi <havasi <at> inf.u-szeged.hu>
2004-06-03 12:46:35 GMT
2004-06-03 12:46:35 GMT
Hi, Now there is only one feature in BBC which is not yet supported in the official JFFS2: model files. I would like to (re)implement it for JFFS2. If someone doesn't know what are model files (and BBC), why they can be usefull: JFFS2 splits the files into 4KB blocks and compresses them individually. 4K can be too small for the compressors to detect correspontendes in the data and compress it effectively. To overcome this problem we can introduce the concept of model-based compressor, which can collect information about the file structure before making the file system image, and can use this (model) information during (de)compressing blocks. We developed a model based compressor - it use binary decision tree as model. It is designed specially for compressing ARM code. In BBC there was a "bbc.conf" file in the root directory of the JFFS2 image containg the names of the model files. At mounting time the system reads this file, and load all the specified files - using their names. David, you wrote me that you don't like this (name-based) solution, because the models are regular files and the (at least the super)user can modify/delete it. You suggested to use inode number instead of names - which is hidden from the user. I thought it over and now I descibe my plan how to implement it in details - before staring to do it: - it will be optional (can be selected by kernel-config) - to identify model-based compressors the highest bit of their JFFS2_COMPR_XXX number will be 1(Continue reading)
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