d/u/geniso: fix rounding to unbreak iso creation

Christian Ehrhardtrequested to merge
paelzer-guest/ipxe:fix-efi-iso-sizes-DEBIAN into master

In certain cases (e.g. toolchain changes) the size of the created EFI blob can end up triggering a rounding down which breaks the build. Example: debian/util/geniso src/bin-combined/ipxe.iso src/bin-i386-pcbios/ipxe.lkrn
src/bin-x86_64-efi/ipxe.efi ... ++ stat -c %s src/bin-x86_64-efi/ipxe.efi

  • blocks=896
  • mkfs.msdos -C src/bin-combined/iso.dir.uayAjK/efi.img 896
  • mmd -i src/bin-combined/iso.dir.uayAjK/efi.img ::efi
  • mmd -i src/bin-combined/iso.dir.uayAjK/efi.img ::efi/boot
  • mcopy -o -i src/bin-combined/iso.dir.uayAjK/efi.img
    src/bin-x86_64-efi/ipxe.efi ::efi/boot/bootx64.efi Disk full

This is due to: echo (((stat -c %s "$EFI") / 1024)) 872 echo (((stat -c %s "$EFI") / 1024 + 55)) 927 echo (((((stat -c %s "$EFI") / 1024 + 55)/32*32))) 896 <- Rounds DOWN

This is due to size+55 => 927 being "just below" the next 32 iteration which would be at 928. In many cases that works fine (I don't know how the +55 was invented, I guess that is for headers). But in some cases it caps too much eventually ending up in a too small image file.

Rounding up (in bash) usually is "N+1/divisor". Therefore if add +1 before the rounding for 32 we'd avoid the issue.

I compared the resulting ISO size with former builds and it was still well within the range of past builds (869,947,948 - now 884).

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