Activating a subphysical driver on failure of hypervisor for operating an I/O device shared by hypervisor and guest OS and virtual computer system

A control method for a physical I/O device, in a computer comprising a processor, a memory, and the I/O device, the I/O device being shared by a hypervisor and a first guest OS,

• the I/O device comprising a physical function and a virtual function, the hypervisor comprising a physical driver for using the physical function, the first guest OS comprising a virtual driver for using the virtual function,
• the control method comprising:
• a first step of acquiring, by the hypervisor, a state of the I/O device via the physical driver;
• a second step of monitoring, by the first guest OS, the hypervisor, thereby determining whether the hypervisor has been brought into a predetermined state or not;
• a third step of activating, by the first guest OS, a sub physical driver for operating the I/O device when the first guest OS determines that the hypervisor has been brought into the predetermined state;
• and
• a fourth step of carrying out, by the first guest OS, transmission of data and reception of data via a queue previously stored on the memory,
• wherein the third step comprises acquiring, by the first guest OS, a state of the I/O device from the virtual driver via the sub physical driver, the state of the I/O device comprising a link state and a bandwidth state for each of the physical function and the virtual function, and then activating the sub physical driver.