sysext: Fix config file section docs and --root=#40063
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yuwata merged 2 commits intosystemd:mainfrom Dec 15, 2025
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pothos
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keszybz
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Thank you for working on this. The general approach seems very reasonable.
The approach with POINTER_MAX is nifty, but I think it's a bit too complicated. After all the parsing is done, we end up with the two arg_ variables correctly initialized. But during parsing, they have "special" values. So e.g. if somebody laters e.g. adds a log statement, or an option to skip config file parsing, or something like that, things will be wrong.
What we normally do in such cases is add an additional variable bool arg_foo_set = false. And then the first parser would set it, and the second parser uses if (arg_foo_set) as the condition whether to overwrite the value. There is no magic intermediate states and it doesn't go awry if any of the steps are skipped.
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Hmm, I think we want the And in the docs, "System/Config Extension" is two words, and our general rules lead to "SysExt" and "ConfExt". |
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Config files for --root= weren't picked up as expected because the --root= flag got parsed after the config file. Switch the order of config file and CLI flag parsing while letting the CLI flags overwrite things set by the config files by tracking state during parsing.
The code uses SysExt and ConfExt for section names but the docs use Sysext and Confext. Align the docs with the code.
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For A/B-updated /etc contents we used a custom overlay mount that provides the default files through a lowerdir loaded from /usr. Since then we upstreamed mutable systemd-confext support and now we can switch to it. This pulls in flatcar/init#138 and flatcar/bootengine#115 together with backported systemd patches that have opened or merged upstream PRs to fix --root= issues and add a refresh skip check to prevent boot disruptions due to the multiple daemon reloads and - more important - the missing atomic remount that would mean /etc is gone for a few milliseconds during boot. The skip logic works best with verity hashes and thus the default confext must be a verity extension image. User-provided confext don't work well yet unless they use verity due to the missing atomic remount and reliance on the skipping logic. We also need to look into stacking order and other mutabiliy settings. The backported systemd patches relate to the following upstream PRs: systemd/systemd#39843 for vpick-Don-t-use-openat-directly-but-resolve-symlinks discover-image-Follow-symlinks-in-a-given-root sysext-Use-correct-image-name-for-extension-release test-Add-tests-for-handling-symlinks-with-systemd-sy Note that the patch in the PR relies on 0859fe3f32774f1e0c787974cc252ff922a1b868 but the backport patch not. systemd/systemd#39980 for sysext-Create-mutable-directory-with-the-right-mode sysext-Skip-refresh-if-no-changes-are-found systemd/systemd#39991 for sysext-Get-verity-user-certs-from-given-root systemd/systemd#40063 for sysext-Fix-config-file-support-with-root which relies on systemd/systemd#38250 for man-sysext.conf-add-systemd-sysext-config-files sysext-introduce-global-config-file sysext-support-ImagePolicy-global-config-option Signed-off-by: Kai Lueke <kailuke@microsoft.com>
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For A/B-updated /etc contents we used a custom overlay mount that provides the default files through a lowerdir loaded from /usr. Since then we upstreamed mutable systemd-confext support and now we can switch to it. This pulls in flatcar/init#138 and flatcar/bootengine#115 together with backported systemd patches that have opened or merged upstream PRs to fix --root= issues and add a refresh skip check to prevent boot disruptions due to the multiple daemon reloads and - more important - the missing atomic remount that would mean /etc is gone for a few milliseconds during boot. The skip logic works best with verity hashes and thus the default confext must be a verity extension image. User-provided confext don't work well yet unless they use verity due to the missing atomic remount and reliance on the skipping logic. We also need to look into stacking order and other mutabiliy settings. The backported systemd patches relate to the following upstream PRs: systemd/systemd#39843 for vpick-Don-t-use-openat-directly-but-resolve-symlinks discover-image-Follow-symlinks-in-a-given-root sysext-Use-correct-image-name-for-extension-release test-Add-tests-for-handling-symlinks-with-systemd-sy Note that the patch in the PR relies on 0859fe3f32774f1e0c787974cc252ff922a1b868 but the backport patch not. systemd/systemd#39980 for sysext-Create-mutable-directory-with-the-right-mode sysext-Skip-refresh-if-no-changes-are-found systemd/systemd#39991 for sysext-Get-verity-user-certs-from-given-root systemd/systemd#40063 for sysext-Fix-config-file-support-with-root which relies on systemd/systemd#38250 for man-sysext.conf-add-systemd-sysext-config-files sysext-introduce-global-config-file sysext-support-ImagePolicy-global-config-option Signed-off-by: Kai Lueke <kailuke@microsoft.com>
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For A/B-updated /etc contents we used a custom overlay mount that provides the default files through a lowerdir loaded from /usr. Since then we upstreamed mutable systemd-confext support and now we can switch to it. This pulls in flatcar/init#138 and flatcar/bootengine#115 together with backported systemd patches that have opened or merged upstream PRs to fix --root= issues and add a refresh skip check to prevent boot disruptions due to the multiple daemon reloads and - more important - the missing atomic remount that would mean /etc is gone for a few milliseconds during boot. The skip logic works best with verity hashes and thus the default confext must be a verity extension image. User-provided confext don't work well yet unless they use verity due to the missing atomic remount and reliance on the skipping logic. We also need to look into stacking order and other mutabiliy settings. The backported systemd patches relate to the following upstream PRs: systemd/systemd#39843 for vpick-Don-t-use-openat-directly-but-resolve-symlinks discover-image-Follow-symlinks-in-a-given-root sysext-Use-correct-image-name-for-extension-release test-Add-tests-for-handling-symlinks-with-systemd-sy Note that the patch in the PR relies on 0859fe3f32774f1e0c787974cc252ff922a1b868 but the backport patch not. systemd/systemd#39980 for sysext-Create-mutable-directory-with-the-right-mode sysext-Skip-refresh-if-no-changes-are-found systemd/systemd#39991 for sysext-Get-verity-user-certs-from-given-root systemd/systemd#40063 for sysext-Fix-config-file-support-with-root which relies on systemd/systemd#38250 for man-sysext.conf-add-systemd-sysext-config-files sysext-introduce-global-config-file sysext-support-ImagePolicy-global-config-option Signed-off-by: Kai Lueke <kailuke@microsoft.com>
pothos
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Dec 18, 2025
For A/B-updated /etc contents we used a custom overlay mount that provides the default files through a lowerdir loaded from /usr. Since then we upstreamed mutable systemd-confext support and now we can switch to it. This pulls in flatcar/init#138 and flatcar/bootengine#115 together with backported systemd patches that have opened or merged upstream PRs to fix --root= issues and add a refresh skip check to prevent boot disruptions due to the multiple daemon reloads and - more important - the missing atomic remount that would mean /etc is gone for a few milliseconds during boot. The skip logic works best with verity hashes and thus the default confext must be a verity extension image. User-provided confext don't work well yet unless they use verity due to the missing atomic remount and reliance on the skipping logic. We also need to look into stacking order and other mutabiliy settings. The backported systemd patches relate to the following upstream PRs: systemd/systemd#39843 for vpick-Don-t-use-openat-directly-but-resolve-symlinks discover-image-Follow-symlinks-in-a-given-root sysext-Use-correct-image-name-for-extension-release test-Add-tests-for-handling-symlinks-with-systemd-sy Note that the patch in the PR relies on 0859fe3f32774f1e0c787974cc252ff922a1b868 but the backport patch not. systemd/systemd#39980 for sysext-Create-mutable-directory-with-the-right-mode sysext-Skip-refresh-if-no-changes-are-found systemd/systemd#39991 for sysext-Get-verity-user-certs-from-given-root systemd/systemd#40063 for sysext-Fix-config-file-support-with-root which relies on systemd/systemd#38250 for man-sysext.conf-add-systemd-sysext-config-files sysext-introduce-global-config-file sysext-support-ImagePolicy-global-config-option Signed-off-by: Kai Lueke <kailuke@microsoft.com>
pothos
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Feb 2, 2026
For A/B-updated /etc contents we used a custom overlay mount that provides the default files through a lowerdir loaded from /usr. Since then we upstreamed mutable systemd-confext support and now we can switch to it. This pulls in flatcar/init#138 and flatcar/bootengine#115 together with backported systemd patches that have opened or merged upstream PRs to fix --root= issues and add a refresh skip check to prevent boot disruptions due to the multiple daemon reloads and - more important - the missing atomic remount that would mean /etc is gone for a few milliseconds during boot. The skip logic works best with verity hashes and thus the default confext must be a verity extension image. User-provided confext don't work well yet unless they use verity due to the missing atomic remount and reliance on the skipping logic. We also need to look into stacking order and other mutabiliy settings. The backported systemd patches relate to the following upstream PRs: systemd/systemd#39843 for vpick-Don-t-use-openat-directly-but-resolve-symlinks discover-image-Follow-symlinks-in-a-given-root sysext-Use-correct-image-name-for-extension-release test-Add-tests-for-handling-symlinks-with-systemd-sy Note that the patch in the PR relies on 0859fe3f32774f1e0c787974cc252ff922a1b868 but the backport patch not. systemd/systemd#39980 for sysext-Create-mutable-directory-with-the-right-mode sysext-Skip-refresh-if-no-changes-are-found systemd/systemd#39991 for sysext-Get-verity-user-certs-from-given-root systemd/systemd#40063 for sysext-Fix-config-file-support-with-root which relies on systemd/systemd#38250 for man-sysext.conf-add-systemd-sysext-config-files sysext-introduce-global-config-file sysext-support-ImagePolicy-global-config-option Signed-off-by: Kai Lueke <kailuke@microsoft.com>
pothos
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Feb 28, 2026
For A/B-updated /etc contents we used a custom overlay mount that provides the default files through a lowerdir loaded from /usr. Since then we upstreamed mutable systemd-confext support and now we can switch to it. This pulls in flatcar/init#138 and flatcar/bootengine#115 together with backported systemd patches that have opened or merged upstream PRs to fix --root= issues and add a refresh skip check to prevent boot disruptions due to the multiple daemon reloads and - more important - the missing atomic remount that would mean /etc is gone for a few milliseconds during boot. The skip logic works best with verity hashes and thus the default confext must be a verity extension image. User-provided confext don't work well yet unless they use verity due to the missing atomic remount and reliance on the skipping logic. We also need to look into stacking order and other mutabiliy settings. The backported systemd patches relate to the following upstream PRs: systemd/systemd#39843 for vpick-Don-t-use-openat-directly-but-resolve-symlinks discover-image-Follow-symlinks-in-a-given-root sysext-Use-correct-image-name-for-extension-release test-Add-tests-for-handling-symlinks-with-systemd-sy Note that the patch in the PR relies on 0859fe3f32774f1e0c787974cc252ff922a1b868 but the backport patch not. systemd/systemd#39980 for sysext-Create-mutable-directory-with-the-right-mode sysext-Skip-refresh-if-no-changes-are-found systemd/systemd#39991 for sysext-Get-verity-user-certs-from-given-root systemd/systemd#40063 for sysext-Fix-config-file-support-with-root which relies on systemd/systemd#38250 for man-sysext.conf-add-systemd-sysext-config-files sysext-introduce-global-config-file sysext-support-ImagePolicy-global-config-option Signed-off-by: Kai Lueke <kailuke@microsoft.com>
pothos
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Feb 28, 2026
For A/B-updated /etc contents we used a custom overlay mount that provides the default files through a lowerdir loaded from /usr. Since then we upstreamed mutable systemd-confext support and now we can switch to it. This pulls in flatcar/init#138 and flatcar/bootengine#115 together with backported systemd patches that have opened or merged upstream PRs to fix --root= issues and add a refresh skip check to prevent boot disruptions due to the multiple daemon reloads and - more important - the missing atomic remount that would mean /etc is gone for a few milliseconds during boot. The skip logic works best with verity hashes and thus the default confext must be a verity extension image. User-provided confext don't work well yet unless they use verity due to the missing atomic remount and reliance on the skipping logic. We also need to look into stacking order and other mutabiliy settings. The backported systemd patches relate to the following upstream PRs: systemd/systemd#39843 for vpick-Don-t-use-openat-directly-but-resolve-symlinks discover-image-Follow-symlinks-in-a-given-root sysext-Use-correct-image-name-for-extension-release test-Add-tests-for-handling-symlinks-with-systemd-sy Note that the patch in the PR relies on 0859fe3f32774f1e0c787974cc252ff922a1b868 but the backport patch not. systemd/systemd#39980 for sysext-Create-mutable-directory-with-the-right-mode sysext-Skip-refresh-if-no-changes-are-found systemd/systemd#39991 for sysext-Get-verity-user-certs-from-given-root systemd/systemd#40063 for sysext-Fix-config-file-support-with-root which relies on systemd/systemd#38250 for man-sysext.conf-add-systemd-sysext-config-files sysext-introduce-global-config-file sysext-support-ImagePolicy-global-config-option Signed-off-by: Kai Lueke <kailuke@microsoft.com>
pothos
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Mar 3, 2026
For A/B-updated /etc contents we used a custom overlay mount that provides the default files through a lowerdir loaded from /usr. Since then we upstreamed mutable systemd-confext support and now we can switch to it. This pulls in flatcar/init#138 and flatcar/bootengine#115 together with backported systemd patches that have opened or merged upstream PRs to fix --root= issues and add a refresh skip check to prevent boot disruptions due to the multiple daemon reloads and - more important - the missing atomic remount that would mean /etc is gone for a few milliseconds during boot. The skip logic works best with verity hashes and thus the default confext must be a verity extension image. User-provided confext don't work well yet unless they use verity due to the missing atomic remount and reliance on the skipping logic. We also need to look into stacking order and other mutabiliy settings. The backported systemd patches relate to the following upstream PRs: systemd/systemd#39843 for vpick-Don-t-use-openat-directly-but-resolve-symlinks discover-image-Follow-symlinks-in-a-given-root sysext-Use-correct-image-name-for-extension-release test-Add-tests-for-handling-symlinks-with-systemd-sy Note that the patch in the PR relies on 0859fe3f32774f1e0c787974cc252ff922a1b868 but the backport patch not. systemd/systemd#39980 for sysext-Create-mutable-directory-with-the-right-mode sysext-Skip-refresh-if-no-changes-are-found systemd/systemd#39991 for sysext-Get-verity-user-certs-from-given-root systemd/systemd#40063 for sysext-Fix-config-file-support-with-root which relies on systemd/systemd#38250 for man-sysext.conf-add-systemd-sysext-config-files sysext-introduce-global-config-file sysext-support-ImagePolicy-global-config-option Signed-off-by: Kai Lueke <kailuke@microsoft.com>
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sysext: Fix config file support with --root=
Config files for --root= weren't picked up as expected because the
--root= flag got parsed after the config file.
Switch the order of config file and CLI flag parsing while letting the
CLI flags overwrite things set by the config files by tracking state
during parsing.
man/sysext.conf: Fix section name to match code
The code uses SysExt and ConfExt for section names but the docs use
Sysext and Confext.
Align the docs with the code.