> On 15 Sep 2018, at 23:48, Liran Alon <liran.alon@xxxxxxxxxx> wrote: > > > >> On 14 Sep 2018, at 18:08, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: >> >> On 14/09/2018 16:31, Liran Alon wrote: >>>> There is still a problem, however, in that the same input stream would >>>> be parsed differently depending on the kernel version. In particular, >>>> if in the future the maximum nested state size grows, you break all >>>> existing save files. >>> >>> I’m not sure I agree with this. >>> 1) Newer kernels should change struct only by utilizing unused fields in current struct >>> or enlarging it with extra fields. It should not change the meaning of existing fields. >> >> Newer kernels will return a larger size, which is stored in >> env->nested_state_len, and the file format depends on it: >> >>> + VMSTATE_VBUFFER_UINT32(env.nested_state, X86CPU, >>> + 0, NULL, >>> + env.nested_state_len), >> > > Oh. I thought that QEMU will just receive to dest buffer only what was sent from source buffer. > I didn’t know that it also enforces that the sizes of the source and dest buffer are equal. > (I thought that dest_buffer_size only needed to be >= src_buffer_size). > > Anyway, my intention here was that QEMU will only enforce (dest_buffer_size >= source_buffer_size) > and if so, receive source buffer into destination buffer. > Is there a simple way to do this in QEMU’s VMSTATE framework without implementing custom save/load callbacks? > One possible, but not so elegant, way to do so is to put env.nested_state_len as part of VMState and change env.nested_state to be declared in VMState as VMSTATE_VBUFFER_ALLOC_UINT32(). Then, make nested_state_post_load() to realloc env.nested_state in size specified by kvm_nested_state_length(). To guarantee that env.nested_state is always at max size that local kernel supports. -Liran
