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make-disk-image: Get proper size for automatic size

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On some filesystems, `du` without `--apparent-size` will not give the
actual size for a file. Using `--apparent-size` will give us the actual
file size.

Though, this is not actually correct still. 1000 × 1 bytes is not 1000
bytes. It is 1000 × ceil(filesize/blockSize)*blockSize.

So instead of adding up the actual file sizes. We are adding up the
block sizes.

Note that this also changes the builder to work with *bytes*, rather
than with any other units. Doing maths on bytes is less likely to go
awry than doing it on other units.
This commit is contained in:
Samuel Dionne-Riel 2021-04-23 04:15:14 -04:00
parent 0ca4f6b739
commit 05c13a03e2
1 changed files with 28 additions and 6 deletions
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34
nixos/lib/make-disk-image.nix
View file

@ -163,6 +163,8 @@ let format' = format; in let
closureInfo = pkgs.closureInfo { rootPaths = [ config.system.build.toplevel channelSources ]; };
blockSize = toString (4 * 1024); # ext4fs block size (not block device sector size)
prepareImage = ''
export PATH=${binPath}
@ -175,6 +177,15 @@ let format' = format; in let
echo $(( "$1" * 512 ))
}
# Given lines of numbers, adds them together
sum_lines() {
local acc=0
while read -r number; do
acc=$((acc+number))
done
echo "$acc"
}
mkdir $out
root="$PWD/root"
@ -235,12 +246,23 @@ let format' = format; in let
${if diskSize == "auto" then ''
${if partitionTableType == "efi" || partitionTableType == "hybrid" then ''
additionalSpace=$(( ($(numfmt --from=iec '${additionalSpace}') + $(numfmt --from=iec '${bootSize}')) / 1000 ))
additionalSpace=$(( ($(numfmt --from=iec '${additionalSpace}') + $(numfmt --from=iec '${bootSize}')) ))
'' else ''
additionalSpace=$(( $(numfmt --from=iec '${additionalSpace}') / 1000 ))
additionalSpace=$(( $(numfmt --from=iec '${additionalSpace}') ))
''}
diskSize=$(( $(set -- $(du -d0 $root); echo "$1") + $additionalSpace ))
truncate -s "$diskSize"K $diskImage
# Compute required space in filesystem blocks
requiredSpace=$(find . ! -type d -exec 'du' '--apparent-size' '--block-size' "${blockSize}" '{}' ';' | cut -f1 | sum_lines)
# Convert to bytes
requiredSpace=$(( requiredSpace * ${blockSize} ))
diskSize=$(( requiredSpace + additionalSpace ))
truncate -s "$diskSize" $diskImage
printf "Automatic disk size...\n"
printf " Space needed: %d bytes\n" $requiredSpace
printf " Additional space: %d bytes\n" $additionalSpace
printf " Disk image size: %d bytes\n" $diskSize
'' else ''
truncate -s ${toString diskSize}M $diskImage
''}
@ -251,9 +273,9 @@ let format' = format; in let
# Get start & length of the root partition in sectors to $START and $SECTORS.
eval $(partx $diskImage -o START,SECTORS --nr ${rootPartition} --pairs)
mkfs.${fsType} -F -L ${label} $diskImage -E offset=$(sectorsToBytes $START) $(sectorsToKilobytes $SECTORS)K
mkfs.${fsType} -b ${blockSize} -F -L ${label} $diskImage -E offset=$(sectorsToBytes $START) $(sectorsToKilobytes $SECTORS)K
'' else ''
mkfs.${fsType} -F -L ${label} $diskImage
mkfs.${fsType} -b ${blockSize} -F -L ${label} $diskImage
''}
echo "copying staging root to image..."