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

[Marek Vasut]

On Monday, February 16, 2015 at 06:33:35 PM, Eric Nelson wrote:
> 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 at 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.

Cool, thanks for explaining :)

Best regards,
Marek Vasut