linux-ext4 - Re: flashing large eMMC partitions with ext4

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Message-ID: <20110725181043.GK3469@thunk.org>
Date:	Mon, 25 Jul 2011 14:10:43 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Round Robinjp <roundrobinjp@...oo.co.jp>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: flashing large eMMC partitions with ext4

On Sat, Jul 23, 2011 at 12:49:28AM +0900, Round Robinjp wrote:
> Hi
> 
> I have a question regarding making ext4 image for
> large eMMC partition.
>  
> We have a 4G partition in our embedded device
> in which we want to use ext4 filesystem.
> But for that we have to create a 4G image.
> flashing this 4G image to the eMMC takes a long
> time. Is there any way to reduce this time?
> 
> For vfat, you can truncate the image leaving only
> non zero-filled blocks which makes the image very
> short and the time for flashing is reduced.
> Is something similar to that possible for ext4?

OK, so it's not obvious what problem you are trying to ask here.

It sounds like Andreas was trying to help you solve the problem of
minimizing the number of blocks written by mke2fs.

I'm guessing the problem is you've already created a file system image
which is 4G, and for which a large number of the blocks are not used,
and you're trying to optimize the amount of time it takes to flash the
image.  Is that right?

The way to do that is to use a program like zerofree.c (google it, or
see attached) to make sure the non-used blocks are zero-filled, and
then use a program like make-sparse.c (see the e2fsprogs sources, in
the contrib directory) to only write the non-zero blocks to the flash
device.

Regards,

						- Ted

View attachment "zerofree.c" of type "text/x-csrc" (3531 bytes)