JFFS2 mount time

[Artem B. Bityuckiy]

Hello Ferenc,

As I understand, you only prepare JFFS2 image with summaries. This is 
great until we do not change anything. For read-only file-systems this 
is OK.

But what if files/direntries are changed/deleted ? Do you write summary 
information dynamically? How are you going to place nodes/direntries to 
different blocks dynamically?

Ferenc Havasi wrote:
> 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

-- 
Best Regards,
Artem B. Bityuckiy,
St.-Petersburg, Russia.