On Tue, Dec 05, 2023 at 09:44:12AM -0300, Fabiano Rosas wrote: > Peter Xu <pet...@redhat.com> writes: > > > On Mon, Dec 04, 2023 at 06:09:16PM -0300, Fabiano Rosas wrote: > >> Right, I got your point. I just think we could avoid designing this new > >> string format by creating new fields with the extra space: > >> > >> typedef struct QEMU_PACKED { > >> uint32_t size; > >> uint8_t runstate[50]; > >> uint8_t unused[50]; > >> RunState state; > >> bool received; > >> } GlobalState; > >> > >> In my mind this works seamlessly, or am I mistaken? > > > > I think what you proposed should indeed work. > > > > Currently it's: > > > > .fields = (VMStateField[]) { > > VMSTATE_UINT32(size, GlobalState), > > VMSTATE_BUFFER(runstate, GlobalState), > > VMSTATE_END_OF_LIST() > > }, > > > > I had a quick look at vmstate_info_buffer, it mostly only get()/put() those > > buffers with its sizeof(), so looks all fine. For sure in all cases we'd > > better test it to verify. > > > > One side note is since we so far use qapi_enum_parse() for the runstate, I > > think the "size" is not ever used.. > > > > If we do want a split, IMHO we can consider making runstate[] even smaller > > to just free up the rest spaces all in one shot: > > > > typedef struct QEMU_PACKED {
[1] > > uint32_t size; > > /* > > * Assuming 16 is good enough to fit all possible runstate strings.. > > * This field must be a string ending with '\0'. > > */ > > uint8_t runstate[16]; > > /* 0x00 when QEMU doesn't support it, or "0"/"1" to reflect its state > > */ > > uint8_t vm_was_suspended[1]; > > /* > > * Still free of use space. Note that we only have 99 bytes for use > > * because the last byte (the 100th byte) must be zero due to legacy > > * reasons, if not it may be set to zero after loaded on dest QEMU. > > */ > > I'd add a 'uint8_t reserved;' to go along with this comment instead of > leaving a hole. Note that "struct GlobalState" is not a binary format but only some internal storage, what really matters is vmstate_globalstate. Here the "uint8_reserved" will be a pure waste of 1 byte in QEMU binary, imho. I think I just copied what you had previously and extended it, logically I don't think we ever need QEMU_PACKED right above [1]. We can also drop "size" directly here, but this can be done later. -- Peter Xu