Increase minimal system image size by 15% to have some free space
We need a better computation of the minimal partition size because right now it just computes the total required size using du (see here) and simply adds 50MB to the root partition have some free space (see here) and 5MB to the boot partition.
In this way we might end up with a partition with no space left because the ext4 partition has a default of 5% reserved blocks for root processes and also the filesystem metadata takes some place.
With this PR I changed the computation to add 15% of the size to the computed one, instead of the 50MB.
I did some tests with/without the change in this PR and I got these results:
with the addition of 50MB:
| img file size | boot partition size | root partition size | root filesystem (size/used/avail) |
|---|---|---|---|
| 333 | 19 | 313 | 296/249/28 |
| 404 | 19 | 384 | 364/306/35 |
| 598 | 19 | 578 | 553/533/0 |
and adding a file with 500MB of random data into the device rootfs, it fails creating the system image with cp: write error: No space left on device
with the 15% addition:
| img file size | boot partition size | root partition size | root filesystem (size/used/avail) |
|---|---|---|---|
| 325 | 19 | 305 | 288/249/20 |
| 407 | 19 | 387 | 367/306/38 |
| 630 | 19 | 610 | 585/533/8.9 |
| 900 | 19 | 880 | 851/769/22 |
It's not the best solution since it depends a lot on the files that gets written but at least it doesn't fail with no space left.
Do you have other ideas/suggestion on how to better compute the minimal size and still have some free space inside?