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/* 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;
}
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