OCPBUGS-43501: coreos-installer iso kargs show broken when using minimal ISO #463

pawanpinjarkar · 2025-08-04T14:07:59Z

Description

This PR enhances the way kernel arguments (kargs) are handled in RHCOS ISOs by updating both isolinux.cfg and coreos/kargs.jso files during minimal ISO generation.

Key changes:

fixIsolinuxConfig now returns the modified config content for reuse instead of writing blindly to disk.
Added fixKargsConfig, which extracts the kernel args starting with rw from isolinux.cfg and updates the embedded coreos/kargs.jso JSON file with correct kernel arguments and offset values.
Introduced helper functions extractBootArgs and buildKargsContent to support safe, consistent parsing and rewriting of kernel args.
Updated test data to include sample kargs.jso.
Extended test coverage to validate both isolinux.cfg and kargs.jso updates in cases with and without the nmstate disk image.

This improves consistency across bootloaders (isolinux and grub), avoids stale coreos.liveiso entries, and ensures correct injection of dynamic rootfs URLs and initrds, especially when including nmstate or other additional initrd images.

How was this code tested?

Unit Tests: Added new tests in rhcos_test.go to validate that:

fixIsolinuxConfig correctly removes coreos.liveiso, adds rw, and appends appropriate initrd paths.
fixKargsConfig correctly parses the kernel args from isolinux.cfg, modifies the kargs.jso file with correct offsets, and embeds updated args.

Assignees

/cc @
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Links

Checklist

Title and description added to both, commit and PR
Relevant issues have been associated
Reviewers have been listed
This change does not require a documentation update (docstring, docs, README, etc)
Does this change include unit tests (note that code changes require unit tests)

…RUB and ISOLINUX config edits Replaced repetitive editFile logic with reusable helper functions: - `replacePatternInFile`: performs regex replacement and returns the updated file content. - `saveFile`: writes content to file with secure permissions (0600). Updated `fixGrubConfig` and `fixIsolinuxConfig` to use these helpers for: - Adding coreos.live.rootfs_url - Removing coreos.liveiso - Modifying initrd lines with optional nmstate ramdisk This improves readability, testability, and maintainability of config mutation logic during ISO generation.

openshift-ci · 2025-08-04T14:08:37Z

[APPROVALNOTIFIER] This PR is NOT APPROVED

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pawanpinjarkar · 2025-08-04T14:09:24Z

/cc @bfournie @zaneb @andfasano

…port - Refactored fixIsolinuxConfig to return modified content for reuse. - Added fixKargsConfig to generate and update kargs.jso with correct kernel args and offset. - Introduced utility functions for extracting boot args and rebuilding kargs.jso. - Enhanced test coverage for both isolinux and kargs config logic. - Updated test data to reflect new kernel argument structure

openshift-ci-robot · 2025-08-04T17:51:46Z

@pawanpinjarkar: This pull request references Jira Issue OCPBUGS-43501, which is invalid:

expected the bug to target the "4.20.0" version, but no target version was set

Comment /jira refresh to re-evaluate validity if changes to the Jira bug are made, or edit the title of this pull request to link to a different bug.

The bug has been updated to refer to the pull request using the external bug tracker.

In response to this:

Description

This PR enhances the way kernel arguments (kargs) are handled in RHCOS ISOs by updating both isolinux.cfg and coreos/kargs.jso files during minimal ISO generation.

Key changes:

fixIsolinuxConfig now returns the modified config content for reuse instead of writing blindly to disk.

Added fixKargsConfig, which extracts the kernel args starting with rw from isolinux.cfg and updates the embedded coreos/kargs.jso JSON file with correct kernel arguments and offset values.

Introduced helper functions extractBootArgs and buildKargsContent to support safe, consistent parsing and rewriting of kernel args.

Updated test data to include sample kargs.jso.

Extended test coverage to validate both isolinux.cfg and kargs.jso updates in cases with and without the nmstate disk image.

This improves consistency across bootloaders (isolinux and grub), avoids stale coreos.liveiso entries, and ensures correct injection of dynamic rootfs URLs and initrds, especially when including nmstate or other additional initrd images.

How was this code tested?

Unit Tests: Added new tests in rhcos_test.go to validate that:

fixIsolinuxConfig correctly removes coreos.liveiso, adds rw, and appends appropriate initrd paths.

fixKargsConfig correctly parses the kernel args from isolinux.cfg, modifies the kargs.jso file with correct offsets, and embeds updated args.

Assignees

/cc @
/cc @

Links

Checklist

Title and description added to both, commit and PR

Relevant issues have been associated

Reviewers have been listed

This change does not require a documentation update (docstring, docs, README, etc)

Does this change include unit tests (note that code changes require unit tests)

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the openshift-eng/jira-lifecycle-plugin repository.

pawanpinjarkar · 2025-08-04T17:52:21Z

/jira refresh

openshift-ci-robot · 2025-08-04T17:52:28Z

@pawanpinjarkar: This pull request references Jira Issue OCPBUGS-43501, which is valid. The bug has been moved to the POST state.

3 validation(s) were run on this bug

bug is open, matching expected state (open)
bug target version (4.20.0) matches configured target version for branch (4.20.0)
bug is in the state ASSIGNED, which is one of the valid states (NEW, ASSIGNED, POST)

Requesting review from QA contact:
/cc @mhanss

In response to this:

/jira refresh

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pawanpinjarkar · 2025-08-04T17:53:19Z

/cherrypick release-4.19, release-4.18, release-4.17, release-4.16

openshift-cherrypick-robot · 2025-08-04T17:53:22Z

@pawanpinjarkar: once the present PR merges, I will cherry-pick it on top of release-4.19, in a new PR and assign it to you.

In response to this:

/cherrypick release-4.19, release-4.18, release-4.17, release-4.16

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openshift-ci · 2025-08-04T18:06:57Z

@pawanpinjarkar: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/edge-test	`83daebe`	link	true	`/test edge-test`

Full PR test history. Your PR dashboard.

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carbonin

This is a bit strange. Generally I'm not sure why this is happening for only one of the boot configs, I don't know where the original offset numbers are coming from and it seems like there's a lot of unnecessary refactoring going on.

carbonin · 2025-08-05T12:28:32Z

pkg/isoeditor/rhcos.go

@@ -18,6 +20,16 @@ const (
 	MinimalVersionForNmstatectl = "4.18.0-ec.0"
 )

+type FileEntry struct {
+	Offset int    `json:"offset"`
+	Path   string `json:"path"`


Are "end" and "pad" just not needed? Maybe add them anyway just for completeness?

I had them added initially, its fair, I will add it back again

carbonin · 2025-08-05T12:29:06Z

pkg/isoeditor/rhcos.go

+	Path   string `json:"path"`
+}
+
+type Config struct {


Can we name this more specifically? This is kargs-specific, right?

right, will do

carbonin · 2025-08-05T12:29:13Z

pkg/isoeditor/isoeditor_suite_test.go

@@ -72,6 +93,7 @@ func createTestFiles(volumeID string) (string, string) {
 	Expect(os.WriteFile(filepath.Join(filesDir, "images/pxeboot/rootfs.img"), []byte("this is rootfs"), 0600)).To(Succeed())
 	Expect(os.WriteFile(filepath.Join(filesDir, "EFI/redhat/grub.cfg"), []byte(testGrubConfig), 0600)).To(Succeed())
 	Expect(os.WriteFile(filepath.Join(filesDir, "isolinux/isolinux.cfg"), []byte(testISOLinuxConfig), 0600)).To(Succeed())
+	Expect(os.WriteFile(filepath.Join(filesDir, "coreos/kargs.jso"), []byte(testKargsConfig), 0600)).To(Succeed())


Suggested change

Expect(os.WriteFile(filepath.Join(filesDir, "coreos/kargs.jso"), []byte(testKargsConfig), 0600)).To(Succeed())

Expect(os.WriteFile(filepath.Join(filesDir, "coreos/kargs.json"), []byte(testKargsConfig), 0600)).To(Succeed())

The filename extension in reality is limited just to 3 chars hence .jso

carbonin · 2025-08-05T13:04:55Z

pkg/isoeditor/rhcos.go

 	if err != nil {
 		return err
 	}
+	offset := 1903
+	if includeNmstateRamDisk {
+		offset = 1923


Where is this number coming from?

The offset was manually calculated during the dev work with the command such as dd if-isolinux.cfg bs=1 skip 1903 when the includeNmstateRamDisk was not included and it was coming to be 1923 when the includeNmstateRamDisk was included.

Is this the same for every ISO version? I would expect this to vary.

If we knew what the grub config file looked like in advance, we could just write the whole file out. We're doing all the replace stuff because we need to be robust against changes in coreos.

I think we need to count the number of characters we're adding/removing and where, then update the offsets/size as appropriate.

carbonin · 2025-08-05T13:06:03Z

pkg/isoeditor/rhcos.go

 			log.WithError(err).Warnf("Failed to edit isolinux config")
 			return err
 		}
+		if err := fixKargsConfig(extractDir, contentWithRamDiskPath, includeNmstateRamDisk); err != nil {


Why does this only apply for isolinux and not grub?

In isolinux.cfg the offset moves (due to adding the ramdisk images at the beginning of the same line.
In grub.cfg the offset stays the same because the line specifying the initrd images currently appears after the one that specifies the kargs.

carbonin · 2025-08-05T13:07:01Z

pkg/isoeditor/rhcos.go

+	if err != nil {
+		return err
+	}
+	if err = saveFile(foundGrubPath, grubFileContent); err != nil {


Why save then edit and save again? Couldn't this just be removed?

carbonin · 2025-08-05T13:09:14Z

pkg/isoeditor/rhcos.go

+}
+
+// saveFile writes the given content to the specified file with 0600 permissions.
+func saveFile(fileName, content string) error {


This function doesn't offer any benefit over just calling os.WriteFile directly. Just deduplicating the permissions hardly seems worth it.

I've noticed that AIs love to do this kind of stuff.

carbonin · 2025-08-05T13:11:40Z

pkg/isoeditor/rhcos.go

 	}

 	return nil
 }

-func fixIsolinuxConfig(rootFSURL, extractDir string, includeNmstateRamDisk bool) error {
+func fixIsolinuxConfig(rootFSURL, extractDir string, includeNmstateRamDisk bool) (string, error) {


Instead of returning the content as a side-effect, could we leave this unchanged then read the file we need after we call the original function?

zaneb · 2025-08-06T10:34:17Z

pkg/isoeditor/rhcos.go

+			// Extract the line content after "append "
+			kernelArgs := strings.TrimPrefix(trimmed, "append ")
+			// Find " rw " (with spaces to avoid partial matches)
+			index := strings.Index(kernelArgs, " rw ")


No reason to think that rw will always be the first arg either.

openshift-ci bot added the size/L Denotes a PR that changes 100-499 lines, ignoring generated files. label Aug 4, 2025

openshift-ci bot requested review from adriengentil and avishayt August 4, 2025 14:08

openshift-ci bot requested review from andfasano, bfournie and zaneb August 4, 2025 14:09

pawanpinjarkar force-pushed the fix-kargs branch from def12db to 83daebe Compare August 4, 2025 17:44

pawanpinjarkar changed the title ~~Fix kargs~~ OCPBUGS-43501: coreos-installer iso kargs show broken when using minimal ISO Aug 4, 2025

openshift-ci-robot added jira/valid-bug Indicates that a referenced Jira bug is valid for the branch this PR is targeting. and removed jira/invalid-bug Indicates that a referenced Jira bug is invalid for the branch this PR is targeting. labels Aug 4, 2025

openshift-ci bot requested a review from mhanss August 4, 2025 17:52

carbonin requested changes Aug 5, 2025

View reviewed changes

openshift-ci bot assigned carbonin Aug 5, 2025

zaneb reviewed Aug 6, 2025

View reviewed changes

	Expect(os.WriteFile(filepath.Join(filesDir, "coreos/kargs.jso"), []byte(testKargsConfig), 0600)).To(Succeed())
	Expect(os.WriteFile(filepath.Join(filesDir, "coreos/kargs.json"), []byte(testKargsConfig), 0600)).To(Succeed())

OCPBUGS-43501: coreos-installer iso kargs show broken when using minimal ISO #463

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OCPBUGS-43501: coreos-installer iso kargs show broken when using minimal ISO #463

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pawanpinjarkar commented Aug 4, 2025

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