On 27.06.24 18:03, David Woodhouse wrote: > > I've updated the tree at > https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/vmclock > (but not yet the qemu one). > > I think I've taken into account all your comments apart from the one > about non-64-bit counters wrapping. I reduced the seq_count to 32 bit > to make room for a 32-bit flags field, added the time type > (UTC/TAI/MONOTONIC) and a smearing hint, with some straw man > definitions for smearing algorithms for which I could actually find > definitions. > > The structure now looks like this: > > > struct vmclock_abi { [...] > > /* > * What time is exposed in the time_sec/time_frac_sec fields? > */ > uint8_t time_type; > #define VMCLOCK_TIME_UNKNOWN 0 /* Invalid / no time exposed */ > #define VMCLOCK_TIME_UTC 1 /* Since 1970-01-01 00:00:00z */ > #define VMCLOCK_TIME_TAI 2 /* Since 1970-01-01 00:00:00z */ > #define VMCLOCK_TIME_MONOTONIC 3 /* Since undefined epoch */ > > /* Bit shift for counter_period_frac_sec and its error rate */ > uint8_t counter_period_shift; > > /* > * Unlike in NTP, this can indicate a leap second in the past. This > * is needed to allow guests to derive an imprecise clock with > * smeared leap seconds for themselves, as some modes of smearing > * need the adjustments to continue even after the moment at which > * the leap second should have occurred. > */ > int8_t leapsecond_direction; > uint64_t leapsecond_tai_sec; /* Since 1970-01-01 00:00:00z */ > > /* > * Paired values of counter and UTC at a given point in time. > */ > uint64_t counter_value; > uint64_t time_sec; /* Since 1970-01-01 00:00:00z */ Nitpick: The comment is not valid any more for TIME_MONOTONIC.
