mirror of
https://github.com/utmapp/UTM.git
synced 2026-10-12 02:24:01 +00:00
osy
2d48f084e6
DiskImageKit can put a copy-on-write layer on an image and remembers what each layer sits on. Use that to freeze the contents of a drive: the layer holding what the guest has written so far is closed off under the name of a snapshot and a fresh one is opened above it for further writes. Layers are kept beside the image as `<image>.<name>.asif`. A layer whose snapshot is deleted cannot be merged away while other layers are stacked on it, so it is only marked as unlinked and is swept once nothing needs it. Attachments are built through the same path so that a drive with layers is opened as the whole stack, and a disposable run adds its throwaway layer on top of it. A stack is only ever opened whole. When one of its layers cannot be read the drive is not attached at all: opening the rest without it would hide what it holds, and falling back to the bare image would write underneath every layer stacked on it. For the same reason a layer to write to is always put in place before the one it replaces goes, and the image under a stack cannot be resized. Nor can a drive with layers be attached read only, which a stack cannot be, or before macOS 27, which cannot read the layers: the image alone is the drive as it was before the first snapshot. Removable media never has layers. Assisted-by: Claude:claude-fable-5-1 Assisted-by: Claude:claude-opus-5