[U-Boot] [PATCH 1/2] gunzip: add gzwrite routine for extracting compresed images to block device

[Eric Nelson <eric.nelson@boundarydevices.com>]

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Hi Tom and Marek,

On 02/16/2015 10:03 AM, Tom Rini wrote:
> On Mon, Feb 16, 2015 at 05:27:59PM +0100, Marek Vasut wrote:
>> On Monday, February 16, 2015 at 12:16:06 AM, Eric Nelson wrote:
>>> Initial filesystem images are generally highly compressible.
>>> 
>>> Add a routine gzwrite that allows gzip-compressed images to be 
>>> written to block devices.
>>> 
>>> Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
>> 
>> Hi!
>> 
>> Stupid question -- can't you compress the thing in DRAM and then
>> use fatwrite or ext4write to write it to FS? Or are you really
>> after writing the data to a raw block device (in which case, you
>> can use similar commands for raw block devices) ?
> 
> I _think_ (and I really hope so otherwise yes, this series needs
> more expanation) that was this adds is the ability to {de,}compress
> on the

(or explanation ;))

Sometimes words fail. I thought that was clear from the commit
message but apparently not.

> fly rather than need to duplicate in DDR which could be 
> hard-to-impossible depending on the size of the data in question.
> 

That's exactly right.

The purpose of this is to aid in loading images onto storage devices
like eMMC where the storage size usually exceeds the size of RAM,
but the compressed image size doesn't.

Even if the compressed image size does exceed RAM, the gzwrite
routine and command give you the ability to do things piecewise,
and save lots of read transfer time.

To give a quick concrete example, we were looking at programming a
relatively small (100's) batch of boards that use a very light
O/S, but have 4GiB of eMMC.

Using ums takes over 25 minutes per board, but loading board.img.gz
and using gzwrite takes 5-6, which is pretty close to optimal given
the speed of the eMMC chip.

My hope is that this is useful as is, and also that the gzwrite
routine can be worked into the fastboot protocol.

Transferring gigabytes of data is slow over USB 2.0 and storage
sizes keep getting bigger.

Regards,


Eric
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