Re: JFFS2: real free capacity of the partition

[Sergei Poselenov <sposelenov@emcraft.com>]

Hello all,

Seems I found why is that happens.
In jffs2_statfs() the wasted_size is excluded
from calculation:
...
    avail = c->dirty_size + c->free_size;
...

Could someone explain for what reason?
Have I understand it right - on the certain conditions, the
wasted space can be converted to dirty space?

Regards,
Sergei

Sergei Poselenov wrote:
> Hello,
> 
> Probably this is a trivial question and won't take much of your time.
> 
> A simple test on a JFFS2 partition:
> 
> # df
> Filesystem           1k-blocks      Used Available Use% Mounted on
> /dev/mtdblock1            1024       376       648  37% /etc
> # dd if=/dev/urandom of=tmp bs=1024 count=2900
> dd: tmp: No space left on device
> # rm tmp
> # df
> Filesystem           1k-blocks      Used Available Use% Mounted on
> /dev/mtdblock1            1024       372       652  36% /etc
> 
> Why additional space appeared?
> 
> I've noted, that this effect:
> - appeared only on the well-used partition, not on the
>   fresh-created one.
> - appeared only after filling up the device
> - appeared only once. On subsequent tests, the free space was
> reported without magic increases.
> 
> 
> Is this is an effect of the JFFS2 garbage collector?
> Is there any method to learn the real available capacity of the
> mounted partition?
> 
> Thanks in advance,
> Sergei
>