Update vendor-sys/illumos to illumos-gate 13758:23432da34147 (dtrace)

References:
  https://www.illumos.org/issues/3021
  https://www.illumos.org/issues/3022
  https://www.illumos.org/issues/3023
  https://www.illumos.org/issues/3024
  https://www.illumos.org/issues/3025
  https://www.illumos.org/issues/3026

Obtained from:	ssh://anonhg@hg.illumos.org/illumos-gate

3 files changed, 191 insertions, 132 deletions

diff --git a/uts/common/dtrace/dtrace.c b/uts/common/dtrace/dtrace.c
index 0c5e4b3..5013661 100644
--- a/uts/common/dtrace/dtrace.c
+++ b/uts/common/dtrace/dtrace.c
@@ -22,6 +22,7 @@
 /*
  * Copyright (c) 2003, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2011, Joyent, Inc. All rights reserved.
+ * Copyright (c) 2012 by Delphix. All rights reserved.
  */
 
 /*
@@ -2401,9 +2402,10 @@ dtrace_speculation_commit(dtrace_state_t *state, processorid_t cpu,
 {
 	dtrace_speculation_t *spec;
 	dtrace_buffer_t *src, *dest;
-	uintptr_t daddr, saddr, dlimit;
+	uintptr_t daddr, saddr, dlimit, slimit;
 	dtrace_speculation_state_t current, new;
 	intptr_t offs;
+	uint64_t timestamp;
 
 	if (which == 0)
 		return;
@@ -2479,7 +2481,37 @@ dtrace_speculation_commit(dtrace_state_t *state, processorid_t cpu,
 	}
 
 	/*
-	 * We have the space; copy the buffer across.  (Note that this is a
+	 * We have sufficient space to copy the speculative buffer into the
+	 * primary buffer.  First, modify the speculative buffer, filling
+	 * in the timestamp of all entries with the current time.  The data
+	 * must have the commit() time rather than the time it was traced,
+	 * so that all entries in the primary buffer are in timestamp order.
+	 */
+	timestamp = dtrace_gethrtime();
+	saddr = (uintptr_t)src->dtb_tomax;
+	slimit = saddr + src->dtb_offset;
+	while (saddr < slimit) {
+		size_t size;
+		dtrace_rechdr_t *dtrh = (dtrace_rechdr_t *)saddr;
+
+		if (dtrh->dtrh_epid == DTRACE_EPIDNONE) {
+			saddr += sizeof (dtrace_epid_t);
+			continue;
+		}
+		ASSERT3U(dtrh->dtrh_epid, <=, state->dts_necbs);
+		size = state->dts_ecbs[dtrh->dtrh_epid - 1]->dte_size;
+
+		ASSERT3U(saddr + size, <=, slimit);
+		ASSERT3U(size, >=, sizeof (dtrace_rechdr_t));
+		ASSERT3U(DTRACE_RECORD_LOAD_TIMESTAMP(dtrh), ==, UINT64_MAX);
+
+		DTRACE_RECORD_STORE_TIMESTAMP(dtrh, timestamp);
+
+		saddr += size;
+	}
+
+	/*
+	 * Copy the buffer across.  (Note that this is a
 	 * highly subobtimal bcopy(); in the unlikely event that this becomes
 	 * a serious performance issue, a high-performance DTrace-specific
 	 * bcopy() should obviously be invented.)
@@ -5951,7 +5983,7 @@ dtrace_probe(dtrace_id_t id, uintptr_t arg0, uintptr_t arg1,
 		if (now - state->dts_alive > dtrace_deadman_timeout) {
 			/*
 			 * We seem to be dead.  Unless we (a) have kernel
-			 * destructive permissions (b) have expicitly enabled
+			 * destructive permissions (b) have explicitly enabled
 			 * destructive actions and (c) destructive actions have
 			 * not been disabled, we're going to transition into
 			 * the KILLED state, from which no further processing
@@ -5979,8 +6011,18 @@ dtrace_probe(dtrace_id_t id, uintptr_t arg0, uintptr_t arg1,
 		tomax = buf->dtb_tomax;
 		ASSERT(tomax != NULL);
 
-		if (ecb->dte_size != 0)
-			DTRACE_STORE(uint32_t, tomax, offs, ecb->dte_epid);
+		if (ecb->dte_size != 0) {
+			dtrace_rechdr_t dtrh;
+			if (!(mstate.dtms_present & DTRACE_MSTATE_TIMESTAMP)) {
+				mstate.dtms_timestamp = dtrace_gethrtime();
+				mstate.dtms_present |= DTRACE_MSTATE_TIMESTAMP;
+			}
+			ASSERT3U(ecb->dte_size, >=, sizeof (dtrace_rechdr_t));
+			dtrh.dtrh_epid = ecb->dte_epid;
+			DTRACE_RECORD_STORE_TIMESTAMP(&dtrh,
+			    mstate.dtms_timestamp);
+			*((dtrace_rechdr_t *)(tomax + offs)) = dtrh;
+		}
 
 		mstate.dtms_epid = ecb->dte_epid;
 		mstate.dtms_present |= DTRACE_MSTATE_EPID;
@@ -6144,7 +6186,9 @@ dtrace_probe(dtrace_id_t id, uintptr_t arg0, uintptr_t arg1,
 				continue;
 
 			switch (act->dta_kind) {
-			case DTRACEACT_SPECULATE:
+			case DTRACEACT_SPECULATE: {
+				dtrace_rechdr_t *dtrh;
+
 				ASSERT(buf == &state->dts_buffer[cpuid]);
 				buf = dtrace_speculation_buffer(state,
 				    cpuid, val);
@@ -6166,10 +6210,23 @@ dtrace_probe(dtrace_id_t id, uintptr_t arg0, uintptr_t arg1,
 				tomax = buf->dtb_tomax;
 				ASSERT(tomax != NULL);
 
-				if (ecb->dte_size != 0)
-					DTRACE_STORE(uint32_t, tomax, offs,
-					    ecb->dte_epid);
+				if (ecb->dte_size == 0)
+					continue;
+
+				ASSERT3U(ecb->dte_size, >=,
+				    sizeof (dtrace_rechdr_t));
+				dtrh = ((void *)(tomax + offs));
+				dtrh->dtrh_epid = ecb->dte_epid;
+				/*
+				 * When the speculation is committed, all of
+				 * the records in the speculative buffer will
+				 * have their timestamps set to the commit
+				 * time.  Until then, it is set to a sentinel
+				 * value, for debugability.
+				 */
+				DTRACE_RECORD_STORE_TIMESTAMP(dtrh, UINT64_MAX);
 				continue;
+			}
 
 			case DTRACEACT_CHILL:
 				if (dtrace_priv_kernel_destructive(state))
@@ -9369,9 +9426,9 @@ dtrace_ecb_add(dtrace_state_t *state, dtrace_probe_t *probe)
 
 	/*
 	 * The default size is the size of the default action: recording
-	 * the epid.
+	 * the header.
 	 */
-	ecb->dte_size = ecb->dte_needed = sizeof (dtrace_epid_t);
+	ecb->dte_size = ecb->dte_needed = sizeof (dtrace_rechdr_t);
 	ecb->dte_alignment = sizeof (dtrace_epid_t);
 
 	epid = state->dts_epid++;
@@ -9470,122 +9527,89 @@ dtrace_ecb_enable(dtrace_ecb_t *ecb)
 static void
 dtrace_ecb_resize(dtrace_ecb_t *ecb)
 {
-	uint32_t maxalign = sizeof (dtrace_epid_t);
-	uint32_t align = sizeof (uint8_t), offs, diff;
 	dtrace_action_t *act;
-	int wastuple = 0;
+	uint32_t curneeded = UINT32_MAX;
 	uint32_t aggbase = UINT32_MAX;
-	dtrace_state_t *state = ecb->dte_state;
 
 	/*
-	 * If we record anything, we always record the epid.  (And we always
-	 * record it first.)
+	 * If we record anything, we always record the dtrace_rechdr_t.  (And
+	 * we always record it first.)
 	 */
-	offs = sizeof (dtrace_epid_t);
-	ecb->dte_size = ecb->dte_needed = sizeof (dtrace_epid_t);
+	ecb->dte_size = sizeof (dtrace_rechdr_t);
+	ecb->dte_alignment = sizeof (dtrace_epid_t);
 
 	for (act = ecb->dte_action; act != NULL; act = act->dta_next) {
 		dtrace_recdesc_t *rec = &act->dta_rec;
+		ASSERT(rec->dtrd_size > 0 || rec->dtrd_alignment == 1);
 
-		if ((align = rec->dtrd_alignment) > maxalign)
-			maxalign = align;
-
-		if (!wastuple && act->dta_intuple) {
-			/*
-			 * This is the first record in a tuple.  Align the
-			 * offset to be at offset 4 in an 8-byte aligned
-			 * block.
-			 */
-			diff = offs + sizeof (dtrace_aggid_t);
-
-			if (diff = (diff & (sizeof (uint64_t) - 1)))
-				offs += sizeof (uint64_t) - diff;
-
-			aggbase = offs - sizeof (dtrace_aggid_t);
-			ASSERT(!(aggbase & (sizeof (uint64_t) - 1)));
-		}
-
-		/*LINTED*/
-		if (rec->dtrd_size != 0 && (diff = (offs & (align - 1)))) {
-			/*
-			 * The current offset is not properly aligned; align it.
-			 */
-			offs += align - diff;
-		}
-
-		rec->dtrd_offset = offs;
-
-		if (offs + rec->dtrd_size > ecb->dte_needed) {
-			ecb->dte_needed = offs + rec->dtrd_size;
-
-			if (ecb->dte_needed > state->dts_needed)
-				state->dts_needed = ecb->dte_needed;
-		}
+		ecb->dte_alignment = MAX(ecb->dte_alignment,
+		    rec->dtrd_alignment);
 
 		if (DTRACEACT_ISAGG(act->dta_kind)) {
 			dtrace_aggregation_t *agg = (dtrace_aggregation_t *)act;
-			dtrace_action_t *first = agg->dtag_first, *prev;
 
-			ASSERT(rec->dtrd_size != 0 && first != NULL);
-			ASSERT(wastuple);
+			ASSERT(rec->dtrd_size != 0);
+			ASSERT(agg->dtag_first != NULL);
+			ASSERT(act->dta_prev->dta_intuple);
 			ASSERT(aggbase != UINT32_MAX);
+			ASSERT(curneeded != UINT32_MAX);
 
 			agg->dtag_base = aggbase;
 
-			while ((prev = first->dta_prev) != NULL &&
-			    DTRACEACT_ISAGG(prev->dta_kind)) {
-				agg = (dtrace_aggregation_t *)prev;
-				first = agg->dtag_first;
-			}
+			curneeded = P2ROUNDUP(curneeded, rec->dtrd_alignment);
+			rec->dtrd_offset = curneeded;
+			curneeded += rec->dtrd_size;
+			ecb->dte_needed = MAX(ecb->dte_needed, curneeded);
 
-			if (prev != NULL) {
-				offs = prev->dta_rec.dtrd_offset +
-				    prev->dta_rec.dtrd_size;
-			} else {
-				offs = sizeof (dtrace_epid_t);
-			}
-			wastuple = 0;
+			aggbase = UINT32_MAX;
+			curneeded = UINT32_MAX;
+		} else if (act->dta_intuple) {
+			if (curneeded == UINT32_MAX) {
+				/*
+				 * This is the first record in a tuple.  Align
+				 * curneeded to be at offset 4 in an 8-byte
+				 * aligned block.
+				 */
+				ASSERT(act->dta_prev == NULL ||
+				    !act->dta_prev->dta_intuple);
+				ASSERT3U(aggbase, ==, UINT32_MAX);
+				curneeded = P2PHASEUP(ecb->dte_size,
+				    sizeof (uint64_t), sizeof (dtrace_aggid_t));
+
+				aggbase = curneeded - sizeof (dtrace_aggid_t);
+				ASSERT(IS_P2ALIGNED(aggbase,
+				    sizeof (uint64_t)));
+			}
+			curneeded = P2ROUNDUP(curneeded, rec->dtrd_alignment);
+			rec->dtrd_offset = curneeded;
+			curneeded += rec->dtrd_size;
 		} else {
-			if (!act->dta_intuple)
-				ecb->dte_size = offs + rec->dtrd_size;
+			/* tuples must be followed by an aggregation */
+			ASSERT(act->dta_prev == NULL ||
+			    !act->dta_prev->dta_intuple);
 
-			offs += rec->dtrd_size;
+			ecb->dte_size = P2ROUNDUP(ecb->dte_size,
+			    rec->dtrd_alignment);
+			rec->dtrd_offset = ecb->dte_size;
+			ecb->dte_size += rec->dtrd_size;
+			ecb->dte_needed = MAX(ecb->dte_needed, ecb->dte_size);
 		}
-
-		wastuple = act->dta_intuple;
 	}
 
 	if ((act = ecb->dte_action) != NULL &&
 	    !(act->dta_kind == DTRACEACT_SPECULATE && act->dta_next == NULL) &&
-	    ecb->dte_size == sizeof (dtrace_epid_t)) {
+	    ecb->dte_size == sizeof (dtrace_rechdr_t)) {
 		/*
-		 * If the size is still sizeof (dtrace_epid_t), then all
+		 * If the size is still sizeof (dtrace_rechdr_t), then all
 		 * actions store no data; set the size to 0.
 		 */
-		ecb->dte_alignment = maxalign;
 		ecb->dte_size = 0;
-
-		/*
-		 * If the needed space is still sizeof (dtrace_epid_t), then
-		 * all actions need no additional space; set the needed
-		 * size to 0.
-		 */
-		if (ecb->dte_needed == sizeof (dtrace_epid_t))
-			ecb->dte_needed = 0;
-
-		return;
 	}
 
-	/*
-	 * Set our alignment, and make sure that the dte_size and dte_needed
-	 * are aligned to the size of an EPID.
-	 */
-	ecb->dte_alignment = maxalign;
-	ecb->dte_size = (ecb->dte_size + (sizeof (dtrace_epid_t) - 1)) &
-	    ~(sizeof (dtrace_epid_t) - 1);
-	ecb->dte_needed = (ecb->dte_needed + (sizeof (dtrace_epid_t) - 1)) &
-	    ~(sizeof (dtrace_epid_t) - 1);
-	ASSERT(ecb->dte_size <= ecb->dte_needed);
+	ecb->dte_size = P2ROUNDUP(ecb->dte_size, sizeof (dtrace_epid_t));
+	ecb->dte_needed = P2ROUNDUP(ecb->dte_needed, (sizeof (dtrace_epid_t)));
+	ecb->dte_state->dts_needed = MAX(ecb->dte_state->dts_needed,
+	    ecb->dte_needed);
 }
 
 static dtrace_action_t *
@@ -9955,7 +9979,7 @@ dtrace_ecb_action_add(dtrace_ecb_t *ecb, dtrace_actdesc_t *desc)
 			break;
 
 		case DTRACEACT_SPECULATE:
-			if (ecb->dte_size > sizeof (dtrace_epid_t))
+			if (ecb->dte_size > sizeof (dtrace_rechdr_t))
 				return (EINVAL);
 
 			if (dp == NULL)
@@ -10068,7 +10092,7 @@ dtrace_ecb_action_remove(dtrace_ecb_t *ecb)
 
 	ecb->dte_action = NULL;
 	ecb->dte_action_last = NULL;
-	ecb->dte_size = sizeof (dtrace_epid_t);
+	ecb->dte_size = 0;
 }
 
 static void
@@ -10339,12 +10363,13 @@ dtrace_buffer_switch(dtrace_buffer_t *buf)
 	caddr_t tomax = buf->dtb_tomax;
 	caddr_t xamot = buf->dtb_xamot;
 	dtrace_icookie_t cookie;
-	hrtime_t now = dtrace_gethrtime();
+	hrtime_t now;
 
 	ASSERT(!(buf->dtb_flags & DTRACEBUF_NOSWITCH));
 	ASSERT(!(buf->dtb_flags & DTRACEBUF_RING));
 
 	cookie = dtrace_interrupt_disable();
+	now = dtrace_gethrtime();
 	buf->dtb_tomax = xamot;
 	buf->dtb_xamot = tomax;
 	buf->dtb_xamot_drops = buf->dtb_drops;
@@ -10639,7 +10664,7 @@ dtrace_buffer_reserve(dtrace_buffer_t *buf, size_t needed, size_t align,
 			if (epid == DTRACE_EPIDNONE) {
 				size = sizeof (uint32_t);
 			} else {
-				ASSERT(epid <= state->dts_necbs);
+				ASSERT3U(epid, <=, state->dts_necbs);
 				ASSERT(state->dts_ecbs[epid - 1] != NULL);
 
 				size = state->dts_ecbs[epid - 1]->dte_size;
@@ -15623,6 +15648,7 @@ dtrace_ioctl(dev_t dev, int cmd, intptr_t arg, int md, cred_t *cr, int *rv)
 			desc.dtbd_drops = buf->dtb_drops;
 			desc.dtbd_errors = buf->dtb_errors;
 			desc.dtbd_oldest = buf->dtb_xamot_offset;
+			desc.dtbd_timestamp = dtrace_gethrtime();
 
 			mutex_exit(&dtrace_lock);
 
@@ -15675,6 +15701,7 @@ dtrace_ioctl(dev_t dev, int cmd, intptr_t arg, int md, cred_t *cr, int *rv)
 		desc.dtbd_drops = buf->dtb_xamot_drops;
 		desc.dtbd_errors = buf->dtb_xamot_errors;
 		desc.dtbd_oldest = 0;
+		desc.dtbd_timestamp = buf->dtb_switched;
 
 		mutex_exit(&dtrace_lock);
 
diff --git a/uts/common/sys/dtrace.h b/uts/common/sys/dtrace.h
index c15799a..fd7612f 100644
--- a/uts/common/sys/dtrace.h
+++ b/uts/common/sys/dtrace.h
@@ -26,6 +26,7 @@
 
 /*
  * Copyright (c) 2011, Joyent, Inc. All rights reserved.
+ * Copyright (c) 2012 by Delphix. All rights reserved.
  */
 
 #ifndef _SYS_DTRACE_H
@@ -919,10 +920,10 @@ typedef struct dtrace_ecbdesc {
  * DTrace Metadata Description Structures
  *
  * DTrace separates the trace data stream from the metadata stream.  The only
- * metadata tokens placed in the data stream are enabled probe identifiers
- * (EPIDs) or (in the case of aggregations) aggregation identifiers.  In order
- * to determine the structure of the data, DTrace consumers pass the token to
- * the kernel, and receive in return a corresponding description of the enabled
+ * metadata tokens placed in the data stream are the dtrace_rechdr_t (EPID +
+ * timestamp) or (in the case of aggregations) aggregation identifiers.  To
+ * determine the structure of the data, DTrace consumers pass the token to the
+ * kernel, and receive in return a corresponding description of the enabled
  * probe (via the dtrace_eprobedesc structure) or the aggregation (via the
  * dtrace_aggdesc structure).  Both of these structures are expressed in terms
  * of record descriptions (via the dtrace_recdesc structure) that describe the
@@ -1017,7 +1018,8 @@ typedef struct dtrace_fmtdesc {
 #define	DTRACEOPT_AGGSORTREV	24	/* reverse-sort aggregations */
 #define	DTRACEOPT_AGGSORTPOS	25	/* agg. position to sort on */
 #define	DTRACEOPT_AGGSORTKEYPOS	26	/* agg. key position to sort on */
-#define	DTRACEOPT_MAX		27	/* number of options */
+#define	DTRACEOPT_TEMPORAL	27	/* temporally ordered output */
+#define	DTRACEOPT_MAX		28	/* number of options */
 
 #define	DTRACEOPT_UNSET		(dtrace_optval_t)-2	/* unset option */
 
@@ -1037,7 +1039,9 @@ typedef struct dtrace_fmtdesc {
  * where user-level wishes the kernel to snapshot the buffer to (the
  * dtbd_data field).  The kernel uses the same structure to pass back some
  * information regarding the buffer:  the size of data actually copied out, the
- * number of drops, the number of errors, and the offset of the oldest record.
+ * number of drops, the number of errors, the offset of the oldest record,
+ * and the time of the snapshot.
+ *
  * If the buffer policy is a "switch" policy, taking a snapshot of the
  * principal buffer has the additional effect of switching the active and
  * inactive buffers.  Taking a snapshot of the aggregation buffer _always_ has
@@ -1050,9 +1054,30 @@ typedef struct dtrace_bufdesc {
 	uint64_t dtbd_drops;			/* number of drops */
 	DTRACE_PTR(char, dtbd_data);		/* data */
 	uint64_t dtbd_oldest;			/* offset of oldest record */
+	uint64_t dtbd_timestamp;		/* hrtime of snapshot */
 } dtrace_bufdesc_t;
 
 /*
+ * Each record in the buffer (dtbd_data) begins with a header that includes
+ * the epid and a timestamp.  The timestamp is split into two 4-byte parts
+ * so that we do not require 8-byte alignment.
+ */
+typedef struct dtrace_rechdr {
+	dtrace_epid_t dtrh_epid;		/* enabled probe id */
+	uint32_t dtrh_timestamp_hi;		/* high bits of hrtime_t */
+	uint32_t dtrh_timestamp_lo;		/* low bits of hrtime_t */
+} dtrace_rechdr_t;
+
+#define	DTRACE_RECORD_LOAD_TIMESTAMP(dtrh)			\
+	((dtrh)->dtrh_timestamp_lo +				\
+	((uint64_t)(dtrh)->dtrh_timestamp_hi << 32))
+
+#define	DTRACE_RECORD_STORE_TIMESTAMP(dtrh, hrtime) {		\
+	(dtrh)->dtrh_timestamp_lo = (uint32_t)hrtime;		\
+	(dtrh)->dtrh_timestamp_hi = hrtime >> 32;		\
+}
+
+/*
  * DTrace Status
  *
  * The status of DTrace is relayed via the dtrace_status structure.  This
diff --git a/uts/common/sys/dtrace_impl.h b/uts/common/sys/dtrace_impl.h
index 3bebd0c..d780082 100644
--- a/uts/common/sys/dtrace_impl.h
+++ b/uts/common/sys/dtrace_impl.h
@@ -26,6 +26,7 @@
 
 /*
  * Copyright (c) 2011, Joyent, Inc. All rights reserved.
+ * Copyright (c) 2012 by Delphix. All rights reserved.
  */
 
 #ifndef _SYS_DTRACE_IMPL_H
@@ -199,15 +200,18 @@ typedef struct dtrace_hash {
  * predicate is non-NULL, the DIF object is executed.  If the result is
  * non-zero, the action list is processed, with each action being executed
  * accordingly.  When the action list has been completely executed, processing
- * advances to the next ECB.  processing advances to the next ECB.  If the
- * result is non-zero; For each ECB, it first determines the The ECB
- * abstraction allows disjoint consumers to multiplex on single probes.
+ * advances to the next ECB. The ECB abstraction allows disjoint consumers
+ * to multiplex on single probes.
+ *
+ * Execution of the ECB results in consuming dte_size bytes in the buffer
+ * to record data.  During execution, dte_needed bytes must be available in
+ * the buffer.  This space is used for both recorded data and tuple data.
  */
 struct dtrace_ecb {
 	dtrace_epid_t dte_epid;			/* enabled probe ID */
 	uint32_t dte_alignment;			/* required alignment */
-	size_t dte_needed;			/* bytes needed */
-	size_t dte_size;			/* total size of payload */
+	size_t dte_needed;			/* space needed for execution */
+	size_t dte_size;			/* size of recorded payload */
 	dtrace_predicate_t *dte_predicate;	/* predicate, if any */
 	dtrace_action_t *dte_action;		/* actions, if any */
 	dtrace_ecb_t *dte_next;			/* next ECB on probe */
@@ -265,27 +269,30 @@ typedef struct dtrace_aggregation {
  * the EPID, the consumer can determine the data layout.  (The data buffer
  * layout is shown schematically below.)  By assuring that one can determine
  * data layout from the EPID, the metadata stream can be separated from the
- * data stream -- simplifying the data stream enormously.
- *
- *      base of data buffer --->  +------+--------------------+------+
- *                                | EPID | data               | EPID |
- *                                +------+--------+------+----+------+
- *                                | data          | EPID | data      |
- *                                +---------------+------+-----------+
- *                                | data, cont.                      |
- *                                +------+--------------------+------+
- *                                | EPID | data               |      |
- *                                +------+--------------------+      |
- *                                |                ||                |
- *                                |                ||                |
- *                                |                \/                |
- *                                :                                  :
- *                                .                                  .
- *                                .                                  .
- *                                .                                  .
- *                                :                                  :
- *                                |                                  |
- *     limit of data buffer --->  +----------------------------------+
+ * data stream -- simplifying the data stream enormously.  The ECB always
+ * proceeds the recorded data as part of the dtrace_rechdr_t structure that
+ * includes the EPID and a high-resolution timestamp used for output ordering
+ * consistency.
+ *
+ *      base of data buffer --->  +--------+--------------------+--------+
+ *                                | rechdr | data               | rechdr |
+ *                                +--------+------+--------+----+--------+
+ *                                | data          | rechdr | data        |
+ *                                +---------------+--------+-------------+
+ *                                | data, cont.                          |
+ *                                +--------+--------------------+--------+
+ *                                | rechdr | data               |        |
+ *                                +--------+--------------------+        |
+ *                                |                ||                    |
+ *                                |                ||                    |
+ *                                |                \/                    |
+ *                                :                                      :
+ *                                .                                      .
+ *                                .                                      .
+ *                                .                                      .
+ *                                :                                      :
+ *                                |                                      |
+ *     limit of data buffer --->  +--------------------------------------+
  *
  * When evaluating an ECB, dtrace_probe() determines if the ECB's needs of the
  * principal buffer (both scratch and payload) exceed the available space.  If