@@ -45,6 +45,10 @@ extern void ktime_get_real_ts64(struct timespec64 *tv);
extern void ktime_get_coarse_ts64(struct timespec64 *ts);
extern void ktime_get_coarse_real_ts64(struct timespec64 *ts);
+/* Multigrain timestamp interfaces */
+extern void ktime_get_coarse_real_ts64_mg(struct timespec64 *ts);
+extern void ktime_get_real_ts64_mg(struct timespec64 *ts);
+
void getboottime64(struct timespec64 *ts);
/*
@@ -114,6 +114,24 @@ static struct tk_fast tk_fast_raw ____cacheline_aligned = {
.base[1] = FAST_TK_INIT,
};
+/*
+ * Multigrain timestamps require tracking the latest fine-grained timestamp
+ * that has been issued, and never returning a coarse-grained timestamp that is
+ * earlier than that value.
+ *
+ * mg_floor represents the latest fine-grained time that has been handed out as
+ * a file timestamp on the system. This is tracked as a monotonic ktime_t, and
+ * converted to a realtime clock value on an as-needed basis.
+ *
+ * Maintaining mg_floor ensures the multigrain interfaces never issue a
+ * timestamp earlier than one that has been previously issued.
+ *
+ * The exception to this rule is when there is a backward realtime clock jump. If
+ * such an event occurs, a timestamp can appear to be earlier than a previous one.
+ */
+
+static __cacheline_aligned_in_smp atomic64_t mg_floor;
+
static inline void tk_normalize_xtime(struct timekeeper *tk)
{
while (tk->tkr_mono.xtime_nsec >= ((u64)NSEC_PER_SEC << tk->tkr_mono.shift)) {
@@ -2394,6 +2412,93 @@ void ktime_get_coarse_real_ts64(struct timespec64 *ts)
}
EXPORT_SYMBOL(ktime_get_coarse_real_ts64);
+/**
+ * ktime_get_coarse_real_ts64_mg - return latter of coarse grained time or floor
+ * @ts: timespec64 to be filled
+ *
+ * Fetch the global mg_floor value, convert it to realtime and
+ * compare it to the current coarse-grained time. Fill @ts with
+ * whichever is latest. Note that this is a filesystem-specific
+ * interface and should be avoided outside of that context.
+ */
+void ktime_get_coarse_real_ts64_mg(struct timespec64 *ts)
+{
+ struct timekeeper *tk = &tk_core.timekeeper;
+ u64 floor = atomic64_read(&mg_floor);
+ ktime_t f_real, offset, coarse;
+ unsigned int seq;
+
+ do {
+ seq = read_seqcount_begin(&tk_core.seq);
+ *ts = tk_xtime(tk);
+ offset = tk_core.timekeeper.offs_real;
+ } while (read_seqcount_retry(&tk_core.seq, seq));
+
+ coarse = timespec64_to_ktime(*ts);
+ f_real = ktime_add(floor, offset);
+ if (ktime_after(f_real, coarse))
+ *ts = ktime_to_timespec64(f_real);
+}
+
+/**
+ * ktime_get_real_ts64_mg - attempt to update floor value and return result
+ * @ts: pointer to the timespec to be set
+ *
+ * Get a monotonic fine-grained time value and attempt to swap it into
+ * mg_floor. If that succeeds then accept the new floor value. If it fails
+ * then another task raced in during the interim time and updated the floor.
+ * Since any update to the floor must be later than the previous floor,
+ * either outcome is acceptable.
+ *
+ * Typically this will be called after calling ktime_get_coarse_real_ts64_mg(),
+ * and determining that the resulting coarse-grained timestamp did not effect
+ * a change in the ctime. Any more recent floor value would effect a change to
+ * the ctime, so there is no need to retry the atomic64_try_cmpxchg() on failure.
+ *
+ * @ts will be filled with the latest floor value, regardless of the outcome of
+ * the cmpxchg. Note that this is a filesystem specific interface and should be
+ * avoided outside of that context.
+ */
+void ktime_get_real_ts64_mg(struct timespec64 *ts)
+{
+ struct timekeeper *tk = &tk_core.timekeeper;
+ ktime_t old = atomic64_read(&mg_floor);
+ ktime_t offset, mono;
+ unsigned int seq;
+ u64 nsecs;
+
+ do {
+ seq = read_seqcount_begin(&tk_core.seq);
+
+ ts->tv_sec = tk->xtime_sec;
+ mono = tk->tkr_mono.base;
+ nsecs = timekeeping_get_ns(&tk->tkr_mono);
+ offset = tk_core.timekeeper.offs_real;
+ } while (read_seqcount_retry(&tk_core.seq, seq));
+
+ mono = ktime_add_ns(mono, nsecs);
+
+ /*
+ * Attempt to update the floor with the new time value. As any
+ * update must be later then the existing floor, and would effect
+ * a change to the ctime from the perspective of the current task,
+ * accept the resulting floor value regardless of the outcome of
+ * the swap.
+ */
+ if (atomic64_try_cmpxchg(&mg_floor, &old, mono)) {
+ ts->tv_nsec = 0;
+ timespec64_add_ns(ts, nsecs);
+ } else {
+ /*
+ * Another task changed mg_floor since "old" was fetched.
+ * "old" has been updated with the latest value of "mg_floor".
+ * That value is newer than the previous floor value, which
+ * is enough to effect a change to the ctime. Accept it.
+ */
+ *ts = ktime_to_timespec64(ktime_add(old, offset));
+ }
+}
+
void ktime_get_coarse_ts64(struct timespec64 *ts)
{
struct timekeeper *tk = &tk_core.timekeeper;