1 files changed, 105 insertions, 0 deletions
diff --git a/external/trace.c b/external/trace.c
new file mode 100644
index 00000000..43ed19bc
--- /dev/null
+++ b/external/trace.c
@@ -0,0 +1,105 @@
+/* Copyright 2013-2014 IBM Corp.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * 	http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+ * implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/* This example code shows how to read from the trace buffer. */
+#include <external/trace.h>
+#include <trace_types.h>
+#include <errno.h>
+
+bool trace_empty(const struct tracebuf *tb)
+{
+	const struct trace_repeat *rep;
+
+	if (tb->rpos == tb->end)
+		return true;
+
+	/*
+	 * If we have a single element only, and it's a repeat buffer
+	 * we've already seen every repeat for (yet which may be
+	 * incremented in future), we're also empty.
+	 */
+	rep = (void *)tb->buf + (tb->rpos & tb->mask);
+	if (tb->end != tb->rpos + sizeof(*rep))
+		return false;
+
+	if (rep->type != TRACE_REPEAT)
+		return false;
+
+	if (rep->num != tb->last_repeat)
+		return false;
+
+	return true;
+}
+
+/* You can't read in parallel, so some locking required in caller. */
+bool trace_get(union trace *t, struct tracebuf *tb)
+{
+	u64 start;
+	size_t len = sizeof(*t) < tb->max_size ? sizeof(*t) : tb->max_size;
+
+	if (trace_empty(tb))
+		return false;
+
+again:
+	/*
+	 * The actual buffer is slightly larger than tbsize, so this
+	 * memcpy is always valid.
+	 */
+	memcpy(t, tb->buf + (tb->rpos & tb->mask), len);
+
+	rmb(); /* read barrier, so we read tb->start after copying record. */
+
+	start = tb->start;
+
+	/* Now, was that overwritten? */
+	if (tb->rpos < start) {
+		/* Create overflow record. */
+		t->overflow.unused64 = 0;
+		t->overflow.type = TRACE_OVERFLOW;
+		t->overflow.len_div_8 = sizeof(t->overflow) / 8;
+		t->overflow.bytes_missed = start - tb->rpos;
+		tb->rpos += t->overflow.bytes_missed;
+		return true;
+	}
+
+	/* Repeat entries need special handling */
+	if (t->hdr.type == TRACE_REPEAT) {
+		u32 num = t->repeat.num;
+
+		/* In case we've read some already... */
+		t->repeat.num -= tb->last_repeat;
+
+		/* Record how many repeats we saw this time. */
+		tb->last_repeat = num;
+
+		/* Don't report an empty repeat buffer. */
+		if (t->repeat.num == 0) {
+			/*
+			 * This can't be the last buffer, otherwise
+			 * trace_empty would have returned true.
+			 */
+			assert(tb->end > tb->rpos + t->hdr.len_div_8 * 8);
+			/* Skip to next entry. */
+			tb->rpos += t->hdr.len_div_8 * 8;
+			tb->last_repeat = 0;
+			goto again;
+		}
+	} else {
+		tb->last_repeat = 0;
+		tb->rpos += t->hdr.len_div_8 * 8;
+	}
+
+	return true;
+}