[U-Boot] dfu: dfu and UBI Volumes

[Pantelis Antoniou]

Hi Tom,

On May 28, 2013, at 6:01 PM, Tom Rini wrote:

> On Tue, May 28, 2013 at 07:50:46AM +0200, Wolfgang Denk wrote:
>> Dear Tom,
>> 
>> In message <20130527233735.GZ17119 at bill-the-cat> you wrote:
>>> 
>>>> Where exactly is this 8 MB limit coming into play?
>>> 
>>> In buffering the data.  We cannot write a chunk of a file to a
>>> filesystem and then append to it, we don't have the API today.
>> 
>> Sorry, I still don't get it. Assuming I have a GiB of RAM, why can I
>> not load a 256 MiB file to RAM, and then write it to a file system?
>> 
>> I have definitely dealt with images and files bigger than 8 MiB in
>> thepast, so I really don't see where any buffer problem could be.
> 
> I thought I might not have been clear about where this limit comes from,
> after I sent the email.  The problem we have, and this is only for
> writing to a filesystem (_not_ writing of a filesystem) is that we do
> not have the API for appending to files, only create/overwrite.  So we
> must read the whole file into memory, and then write it out.  The DFU
> protocol doesn't have (I would swear anyhow) a part where it says "I'm
> about to send you a blob of X bytes", so we cannot know at the start how
> much data is coming our way.
> 
> Today we "solve" this with a statically defined
> CONFIG_SYS_DFU_MAX_FILE_SIZE.  Looking at things again, I think this is
> buggy right now in that we need to also whack DFU_DATA_BUF_SIZE to also
> be that same value.  Going forward, we may be able to switch this to
> (and both of these are off the top of my head) a getenv to see how much
> space to malloc, or just making it a malloc and adding some compile-time
> check to ensure that the malloc area is at least as big as
> CONFIG_SYS_DFU_MAX_FILE_SIZE.
> 

Correct, the DFU protocol doesn't have a method to inform you before hand
about the size of the transfer about to happen.

The only possible solution I see at this point is to have an environment
variable, i.e. dfubuf that controls the size of the buffer.

Upon start of a dfu transfer we can allocate the buffer, and do our
thing.

> -- 
> Tom

Regards

-- Pantelis