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Fix loopback partitions unavailable in docker environment #368

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Fix loopback partitions unavailable in docker environment #368

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019b345
Using kpartx for partition detection inside docker
Mar 6, 2025
c1c71cc
updating ubuntu image, as it is not available anymore
Mar 6, 2025
2771ca4
Debian Trixie Support:
Jan 5, 2026
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24 changes: 19 additions & 5 deletions builder/step_map_image.go
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ import (
"github.com/hashicorp/packer-plugin-sdk/packer"
)

// StepMapImage maps system image to /dev/loopX
// StepMapImage maps a system image to a free loop device and creates partition mappings via kpartx.
type StepMapImage struct {
ResultKey string
loopDevice string
Expand All @@ -26,15 +26,21 @@ func (s *StepMapImage) Run(_ context.Context, state multistep.StateBag) multiste
ui.Message(fmt.Sprintf("mapping image %s to free loopback device", image))

out, err := exec.Command("losetup", "--find", "--partscan", "--show", image).CombinedOutput()
if err != nil {
ui.Error(fmt.Sprintf("Error running losetup: %v: %s", err, string(out)))
return multistep.ActionHalt
}
s.loopDevice = strings.TrimSpace(string(out))

out, err = exec.Command("kpartx", "-av", s.loopDevice).CombinedOutput()
if err != nil {
ui.Error(fmt.Sprintf("error losetup --find --partscan %v: %s", err, string(out)))
ui.Error(fmt.Sprintf("Error running kpartx: %v: %s", err, string(out)))
return multistep.ActionHalt
}
s.loopDevice = strings.Trim(string(out), "\n")
s.loopDevice = "/dev/mapper/" + strings.TrimPrefix(s.loopDevice, "/dev/")

state.Put(s.ResultKey, s.loopDevice)
ui.Message(fmt.Sprintf("image %s mapped to %s", image, s.loopDevice))
ui.Message(fmt.Sprintf("Image %s mapped to %s", image, s.loopDevice))

return multistep.ActionContinue
}
Expand All @@ -45,7 +51,15 @@ func (s *StepMapImage) Cleanup(state multistep.StateBag) {

// Warning: Busy device will prevent detaching loop device from file
// https://github.com/util-linux/util-linux/issues/484
out, err := exec.Command("losetup", "--detach", s.loopDevice).CombinedOutput()
if s.loopDevice == "" {
return
}
// Remove kpartx mappings.
out, err := exec.Command("kpartx", "-d", s.loopDevice).CombinedOutput()
if err != nil {
ui.Error(fmt.Sprintf("Error cleaning up kpartx mappings for %s: %v: %s", s.loopDevice, err, string(out)))
}
out, err = exec.Command("losetup", "--detach", s.loopDevice).CombinedOutput()
if err != nil {
ui.Error(fmt.Sprintf("error while unmounting loop device %v: %s", err, string(out)))
}
Expand Down
5 changes: 3 additions & 2 deletions docker/Dockerfile
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
# Source for qemu-user-static >7.0
FROM public.ecr.aws/ubuntu/ubuntu:lunar as qemu_binaries
FROM public.ecr.aws/ubuntu/ubuntu:noble as qemu_binaries

# hadolint ignore=DL3008
RUN apt-get update -qq \
Expand Down Expand Up @@ -43,13 +43,14 @@ RUN if [ "$(uname -m)" = "aarch64" ]; then PACKER_ARCH="arm64"; else PACKER_ARCH
# COMPRESS WITH UPX
RUN upx-ucl --lzma /build/packer-builder-arm /bin/packer

FROM public.ecr.aws/lts/ubuntu:jammy
FROM public.ecr.aws/lts/ubuntu:noble

# hadolint ignore=DL3008
RUN apt-get update -qq \
&& apt-get install -qqy --no-install-recommends \
ca-certificates \
dosfstools \
e2fsprogs \
fdisk \
gdisk \
kpartx \
Expand Down