JFFS

JFFS

[David Mackay]

Hi,

Could someone shed some light on a difficulty we are
experiencing? We have an X86 board with 8meg of flash
and 16meg of RAM. As you can see from the df output
below most is mounted as / with a meg or so as /var
and a 2meg ram disk mounted as /var/tmp. However we
are finding that the df output differs substantially
from the actual usage, as you can see from the du on
the var directory tree we should only be using 132K
whereas df suggests 552K. We understand that the file
system itself will need a little space and on top of
that there will be some wastage. Indeed if we fill
/var up with files it does clean itself to an extent
but we are still some 40% short.

As we use /var for FIFO data storage on this system
(many 8-32K files) we need a reliable predictable free
space estimation in order to be able to maximise the
number of stored files before we delete to add new.
Therefore a better understanding of the inner workings
of JFFS would be appreciated.

arcom@ME /var$ du -s *
3       home
0       lock
0       log
129     me
0       run
34      tmp
arcom@ME /var$ df
Filesystem           1k-blocks      Used Available
Use% Mounted on
/dev/root                 5888      5524       364 
94% /
/dev/mtdblock1            1152       552       600 
48% /var
/dev/ram0                 2011        52      1857  
3% /var/tmp
arcom@ME /var$ 

Many thanks, David

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Re: JFFS

[David Woodhouse]

monitoreurope@yahoo.co.uk said:
>  As we use /var for FIFO data storage on this system (many 8-32K
> files) we need a reliable predictable free space estimation in order
> to be able to maximise the number of stored files before we delete to
> add new. Therefore a better understanding of the inner workings of
> JFFS would be appreciated.

We make stuff up in jffs2_statfs(). You may be able to improve it if you 
include c->erasing_size in the calculation of 'avail', and you'll probably 
want to include the size of the blocks on the erase_pending_list too.

--
dwmw2

Re: JFFS

[David Mackay]

 --- David Woodhouse <dwmw2@infradead.org> wrote: > 
> monitoreurope@yahoo.co.uk said:
> >  As we use /var for FIFO data storage on this
> system (many 8-32K
> > files) we need a reliable predictable free space
> estimation in order
> > to be able to maximise the number of stored files
> before we delete to
> > add new. Therefore a better understanding of the
> inner workings of
> > JFFS would be appreciated.
> 
> We make stuff up in jffs2_statfs(). You may be able
> to improve it if you 
> include c->erasing_size in the calculation of
> 'avail', and you'll probably 
> want to include the size of the blocks on the
> erase_pending_list too.

David,

Is there a method by which we could call the garbage
collection function on demand? I ask because our 1 meg
partion mounted as /var will be quite static as we
have a ram disk for transient info. Therfore we will
probably only do a write every 1 hour or so. It would
therfore pay us to link garbage collection with our
FIFO clean up.

David.

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Re: JFFS

[David Woodhouse]

monitoreurope@yahoo.co.uk said:
>  Is there a method by which we could call the garbage collection
> function on demand? I ask because our 1 meg partion mounted as /var
> will be quite static as we have a ram disk for transient info.
> Therfore we will probably only do a write every 1 hour or so. It would
> therfore pay us to link garbage collection with our FIFO clean up.

You can make the GC thread wake up by sending it a SIGHUP. It'll only do 
one operation and then sleep again, though.

What you probably want is a way to tune the thresholds which trigger GC.

--
dwmw2

Jffs

[lp4u]

Hi,

how to mount jffs on a NAND?
how to write a file in a NAND, using jffs?
what's a jffs image ?

Thanks,
Lorenzo

Re: Jffs

[Michael Moedt]

> Hi,
> 
> how to mount jffs on a NAND?
> how to write a file in a NAND, using jffs?
> what's a jffs image ?
> 

Please go to linux-mtd.infradead.org, and follow the Documentation
links.

Mike

JFFS

[Jason Walker]

Ok, so what does it take to put jffs on a DOC? :)
I did a dd to my DOC...when it booted it said "no mtd devices found" and
didn't mount.. Does it lok for a different device?

Jason Walker
Network Engineer
US Wireless Online
www.uswo.net