1 files changed, 62 insertions, 0 deletions

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index deb82a4fc312..4b3b84cd71a1 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -95,3 +95,65 @@ struct perf_evsel *perf_evlist__id2evsel(struct perf_evlist *evlist, u64 id)
                         return sid->evsel;
         return NULL;
 }
+
+event_t *perf_evlist__read_on_cpu(struct perf_evlist *evlist, int cpu)
+{
+        /* XXX Move this to perf.c, making it generally available */
+        unsigned int page_size = sysconf(_SC_PAGE_SIZE);
+        struct perf_mmap *md = &evlist->mmap[cpu];
+        unsigned int head = perf_mmap__read_head(md);
+        unsigned int old = md->prev;
+        unsigned char *data = md->base + page_size;
+        event_t *event = NULL;
+        int diff;
+
+        /*
+         * If we're further behind than half the buffer, there's a chance
+         * the writer will bite our tail and mess up the samples under us.
+         *
+         * If we somehow ended up ahead of the head, we got messed up.
+         *
+         * In either case, truncate and restart at head.
+         */
+        diff = head - old;
+        if (diff > md->mask / 2 || diff < 0) {
+                fprintf(stderr, "WARNING: failed to keep up with mmap data.\n");
+
+                /*
+                 * head points to a known good entry, start there.
+                 */
+                old = head;
+        }
+
+        if (old != head) {
+                size_t size;
+
+                event = (event_t *)&data[old & md->mask];
+                size = event->header.size;
+
+                /*
+                 * Event straddles the mmap boundary -- header should always
+                 * be inside due to u64 alignment of output.
+                 */
+                if ((old & md->mask) + size != ((old + size) & md->mask)) {
+                        unsigned int offset = old;
+                        unsigned int len = min(sizeof(*event), size), cpy;
+                        void *dst = &evlist->event_copy;
+
+                        do {
+                                cpy = min(md->mask + 1 - (offset & md->mask), len);
+                                memcpy(dst, &data[offset & md->mask], cpy);
+                                offset += cpy;
+                                dst += cpy;
+                                len -= cpy;
+                        } while (len);
+
+                        event = &evlist->event_copy;
+                }
+
+                old += size;
+        }
+
+        md->prev = old;
+        return event;
+}