Handling sync system calls

[Charles Manning <manningc2@actrix.gen.nz>]

Hi all

I have written a so-called "cechkpointing" mechanism for the YAFFS2 file 
system that stores a snapshot of the fs structure in some spare flash. When 
the filesystem gets remounted, this info replaces the normal scanning process 
and thus significantly speeds up mounting.

At this stage I have managed to attach the "checkpoint" writting to put_super 
so that the info is stored during a umount, but have had some problems trying 
to do the same with getting this to work with a sync call.

I don't really want the checkpoint data to get written too often as this will 
slow down the fs and cause extra flashh wear. I really only want it to happen 
as part of an explicite sync().

I tried attaching the checkpointing to the write_super() and sync_fs() 
methods, but these either caused writing more often than I needed, or nothing 
happened because sb->s_dirt was not set.

As a final twist it would be really handy for the solution to work with both 
2.4 and 2.6 kernels. A lot of embedded systems still run 2.4.x.

ANy pointers on how to proceed much appreciated.

Thanx

-- Charles