Fix usbf storage write without CoW device #561
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To distinguish which CoW operation failed due to a missing CoW device, we introduce a dedicated exception. As these exceptions cannot easily be thrown across the RPC boundary, we catch them in the exposed interface and re-throw as standard library exceptions. Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
When closing the image, we currently only check if the rollback feature is implemented, but not if it is configured. On QEMU this is fine, as the rollback implementation itself unconditionally can be executed (if not configured, the call is a noop). However, on usbf the call checks if a CoW device is configured and raises otherwise. As we cannot check if a device is configured at the callsite in image, we introduce a parameter to the rollback method to ignore missing devices. For the sake of completeness, we implement the same also for the commit method. Closes: siemens#560 Fixes: 02dd6b0 ("feat(storage): add initial support for commit/rollback") Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
We currently silently ignore CoW operations with the QEMU backend in case the CoW device is not configured. This is different from the usbf backend, which raises in this case. To keep both implementations in sync, we now also raise in QEMU if a CoW operation shall be performed without having a device (and this case is not explicitly ignored via ignore_missing). Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
chombourger
approved these changes
Jan 9, 2026
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The bug arises from inconsistent semantics of the storage backends (usbf and qemu) regarding if a CoW device is needed when calling CoW operations or not. We now align these so that the caller does not need to care.
closes: #560