Re: [OE-core] [PATCH 0/3] image_types: use IMAGE_FILE_MAXSIZE variable to create fixed partition size

[Alexandre Belloni <alexandre.belloni@bootlin.com>]

Hello,

On 04/06/2023 14:37:52+0200, Charles-Antoine Couret via lists.openembedded.org wrote:
> In case of fixed partitionning where the rootfs partition can't exceed an
> amount of bytes, there is currently no automatic and no generic way to have
> this requirement met in any case.
> 
> Until now, ROOTFS_SIZE value got from directory_size() does not takes into account
> the size of required metadata for the filesystem itself (and does not work well
> for other block size than 4k BTW).
> Obviously it's a difficult task which depends on rootfs size and filesystem type.
> 
> The workaround was to set IMAGE_OVERHEAD_FACTOR and IMAGE_ROOTFS_EXTRA_SPACE
> to add the required extra margins. But when the final rootfs is closed to the
> maximum size, it's difficult to adjust them correctly  And if you remove
> or add new recipes in your image, you've to recompute these margins to have enough
> space for these metadata when the rootfs is small, and to not have too big final
> file when the rootfs is big.
> 
> It's cumbersome and error prone to just have a build failure when the final output
> can't be flashed into the partition.
> 
> The solution is to follow how it's implemented in buildroot by having a
> specific variable, here IMAGE_FILE_MAXSIZE, to create the final sparse file
> and trying to fill it with the content of rootfs. If there is enough space,
> margins are well compressed and does not consume space in the filesystem.
> If there is no enough space, an error is triggered to warm the developer before
> trying to use it in the device.
> 
> If IMAGE_FILE_MAXSIZE is not set, the idea is to keep the previous behaviour
> for compatibility reason and to met other requirements.

It would be great if you could add test cases that ensure that the
generated images are indeed fitting the size.

> 
> Charles-Antoine Couret (3):
>   image_types: use IMAGE_FILE_MAXSIZE variable for ext2/3/4 image types
>   image_types: use IMAGE_FILE_MAXSIZE variable for btrfs image types
>   image_types: use IMAGE_FILE_MAXSIZE variable for f2fs image types
> 
>  meta/classes-recipe/image_types.bbclass | 34 +++++++++++++++++++------
>  1 file changed, 26 insertions(+), 8 deletions(-)
> 
> -- 
> 2.40.1
> 

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-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com