RFC: Devices for files and partitions

[AKASHI Takahiro]

On Tue, Jul 06, 2021 at 05:05:19PM -0600, Simon Glass wrote:
> Hi,
> 
> At present U-Boot avoids the concept of 'opening' a file. Being in a
> bootloader environment, it is normally better to take the action
> immediately and avoid any caching, for example, since there is no
> background task to clean up afterwards.
> 
> Having said that, the concept of a file is quite useful, for example
> to write the output of a command to a file, or to open a file and read
> it a line at a time.
> 
> Another case has come to light in that EFI wants to access files using
> a file handle. This currently uses parallel data structures and does
> not map very well in U-Boot.
> 
> Finally, partitions has a similar issue, where defining them as a
> device can have benefits, e.g. to specify the device to use directly,
> rather than with the 'type dev:part' approach, perhaps providing them
> in the devicetree, etc.
> 
> For the above reasons, I propose that we implement, as an option,
> support for files and partitions within driver model.

+1

# Nobody has commented yet :)

Regarding a "file (or file descriptor)", we have already implemented
the same concept in efi_loader. So technically, it won't be a hard-work.
Regarding "partitions as udevice," I have posted an experimental
patch [1]. So it must also be feasible.

One of my concerns is what benefit end users may enjoy.

-Takahiro Akashi

[1] https://lists.denx.de/pipermail/u-boot/2019-February/357937.html
    https://lists.denx.de/pipermail/u-boot/2019-February/357934.html

> Regards,
> Simon