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Save and restore (also known as suspend and resume) permits a snapshot to be taken of a guest's state that can later be resumed. In the current implementation, bhyve(8) creates a UNIX domain socket that is used by bhyvectl(8) to send a request to save a snapshot (and optionally exit after the snapshot has been taken). A snapshot currently consists of two files: the first holds a copy of guest RAM, and the second file holds other guest state such as vCPU register values and device model state. To resume a guest, bhyve(8) must be started with a matching pair of command line arguments to instantiate the same set of device models as well as a pointer to the saved snapshot. While the current implementation is useful for several uses cases, it has a few limitations. The file format for saving the guest state is tied to the ABI of internal bhyve structures and is not self-describing (in that it does not communicate the set of device models present in the system). In addition, the state saved for some device models closely matches the internal data structures which might prove a challenge for compatibility of snapshot files across a range of bhyve versions. The file format also does not currently support versioning of individual chunks of state. As a result, the current file format is not a fixed binary format and future revisions to save and restore will break binary compatiblity of snapshot files. The goal is to move to a more flexible format that adds versioning, etc. and at that point to commit to providing a reasonable level of compatibility. As a result, the current implementation is not enabled by default. It can be enabled via the WITH_BHYVE_SNAPSHOT=yes option for userland builds, and the kernel option BHYVE_SHAPSHOT. Submitted by: Mihai Tiganus, Flavius Anton, Darius Mihai Submitted by: Elena Mihailescu, Mihai Carabas, Sergiu Weisz Relnotes: yes Sponsored by: University Politehnica of Bucharest Sponsored by: Matthew Grooms (student scholarships) Sponsored by: iXsystems Differential Revision: https://reviews.freebsd.org/D19495
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