JFFS2 mount time

[Ferenc Havasi]

Dear All,

Here is the latest version of our mount time improvement.

Using of it:
- apply this patch on the latest version of MTD
- compile sumtool (make command in mtd/util)
- make your JFFS2 image as before (or you can use already created images 
as well)
- run sumtool to insert summary information, for example:
   ./sumtool -i original.jffs2 -o new.jffs2 -e128KiB
- recompile your kernel with "JFFS2 inode summary support"

Jarkko made a measurement on a real NAND device: his JFFS2 image was 
120819928 (115M), after running sumtool the new image was 123338752 (117M).

Using the original mount time was 55 sec, with the new image it is only 
8.5 sec.

It works very similar as our previous improvement: stores special 
information at the end of the erase blocks, and at mount time if there 
is this kind of information the scaning of the erase block is unneccessary.

New things compared to our previous improvement:
- it was fully rewritten
- we separated the user space tool from mkfs. (sumtool)
- sumtool now not only inserts the summary information but also make 
some node-reordering. There will be two kind of erase blocks: in the 
"first type" there will be only jffs2_raw_inodes, and all other node 
(jffs2_raw_dirent) will be stored in the "second type". It generates 
summary at the end of all "fist type" eraseblock. (the "second type" 
will be scanned as before, because all information is needed in 
jffs_raw_dirent at mount time)

Ceratinly all of these things are optional (as you can see above you 
have to select it from kernel config). The JFFS2 image produced by 
sumtool is also usable with previous kernel because the summary node is 
JFFS2_FEATURE_RWCOMPAT_DELETE.

I think it can be usefull not only for us. David, may I commit it to the 
CVS?

Regards,
Ferenc
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