On Wednesday 16 November 2011 16:20:47 张磊 wrote:
> i'm reading the yaffs2's sourcecode,and i'm puzzling about the check point
> mechnism.

> 1.in struct yaffs_dev ,it's member checkpt_buffer,it seems storing
> checkpoint data,and checkpt_byte_offs stores the offset of each check point
> data.(i'm right?) in funciton write checkpoint to yaffs_dev and read
> checkpoint from yaffs_dev,after write/read check point
> data,checkpt_byte_offs always increace, this is why i'm puzzling,can
> someone tell me why,thank very much.


The checkpoint data is read or written as a stream. The checkpoint buffer is 
just a buffer used to hold the data to build up page aligned data. See the 
functions in yaffs_checkptrw.c.


> 2.as the checkpoint data is not write to flash immediately,if suddenly the
> device lost power and the checkpoint has not been synchronized while many
> successful opeartion has down.then reboot the device ,how does yaffs2 work?
> use the checkpoint data to recover or scan flash  to recover? and how
> yaffs2 detectes?

If there is no valid checkpoint then yaffs scans the flash instead. This is 
detected by not finding any, or enough, checkpoint data when reading the 
checkpoint.

-- Charles