3 files changed, 119 insertions, 10 deletions

diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index 5042093d5213..aa79fb8a16d4 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -55,6 +55,7 @@ struct record_opts {
         bool         sample_intr_regs;
         bool         running_time;
         bool         full_auxtrace;
+        bool         auxtrace_snapshot_mode;
         unsigned int freq;
         unsigned int mmap_pages;
         unsigned int auxtrace_mmap_pages;
@@ -62,6 +63,8 @@ struct record_opts {
         u64          branch_stack;
         u64          default_interval;
         u64          user_interval;
+        size_t       auxtrace_snapshot_size;
+        const char   *auxtrace_snapshot_opts;
         bool         sample_transaction;
         unsigned     initial_delay;
         bool         use_clockid;
diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
index 129371048fc1..df66966cfde7 100644
--- a/tools/perf/util/auxtrace.c
+++ b/tools/perf/util/auxtrace.c
@@ -504,6 +504,29 @@ void auxtrace_record__free(struct auxtrace_record *itr)
                 itr->free(itr);
 }
 
+int auxtrace_record__snapshot_start(struct auxtrace_record *itr)
+{
+        if (itr && itr->snapshot_start)
+                return itr->snapshot_start(itr);
+        return 0;
+}
+
+int auxtrace_record__snapshot_finish(struct auxtrace_record *itr)
+{
+        if (itr && itr->snapshot_finish)
+                return itr->snapshot_finish(itr);
+        return 0;
+}
+
+int auxtrace_record__find_snapshot(struct auxtrace_record *itr, int idx,
+                                   struct auxtrace_mmap *mm,
+                                   unsigned char *data, u64 *head, u64 *old)
+{
+        if (itr && itr->find_snapshot)
+                return itr->find_snapshot(itr, idx, mm, data, head, old);
+        return 0;
+}
+
 int auxtrace_record__options(struct auxtrace_record *itr,
                              struct perf_evlist *evlist,
                              struct record_opts *opts)
@@ -520,6 +543,19 @@ u64 auxtrace_record__reference(struct auxtrace_record *itr)
         return 0;
 }
 
+int auxtrace_parse_snapshot_options(struct auxtrace_record *itr,
+                                    struct record_opts *opts, const char *str)
+{
+        if (!str)
+                return 0;
+
+        if (itr)
+                return itr->parse_snapshot_options(itr, opts, str);
+
+        pr_err("No AUX area tracing to snapshot\n");
+        return -EINVAL;
+}
+
 struct auxtrace_record *__weak
 auxtrace_record__init(struct perf_evlist *evlist __maybe_unused, int *err)
 {
@@ -1077,16 +1113,26 @@ int perf_event__process_auxtrace_error(struct perf_tool *tool __maybe_unused,
         return 0;
 }
 
-int auxtrace_mmap__read(struct auxtrace_mmap *mm, struct auxtrace_record *itr,
-                        struct perf_tool *tool, process_auxtrace_t fn)
+static int __auxtrace_mmap__read(struct auxtrace_mmap *mm,
+                                 struct auxtrace_record *itr,
+                                 struct perf_tool *tool, process_auxtrace_t fn,
+                                 bool snapshot, size_t snapshot_size)
 {
-        u64 head = auxtrace_mmap__read_head(mm);
-        u64 old = mm->prev, offset, ref;
+        u64 head, old = mm->prev, offset, ref;
         unsigned char *data = mm->base;
         size_t size, head_off, old_off, len1, len2, padding;
         union perf_event ev;
         void *data1, *data2;
 
+        if (snapshot) {
+                head = auxtrace_mmap__read_snapshot_head(mm);
+                if (auxtrace_record__find_snapshot(itr, mm->idx, mm, data,
+                                                   &head, &old))
+                        return -1;
+        } else {
+                head = auxtrace_mmap__read_head(mm);
+        }
+
         if (old == head)
                 return 0;
 
@@ -1106,6 +1152,9 @@ int auxtrace_mmap__read(struct auxtrace_mmap *mm, struct auxtrace_record *itr,
         else
                 size = mm->len - (old_off - head_off);
 
+        if (snapshot && size > snapshot_size)
+                size = snapshot_size;
+
         ref = auxtrace_record__reference(itr);
 
         if (head > old || size <= head || mm->mask) {
@@ -1153,18 +1202,34 @@ int auxtrace_mmap__read(struct auxtrace_mmap *mm, struct auxtrace_record *itr,
 
         mm->prev = head;
 
-        auxtrace_mmap__write_tail(mm, head);
-        if (itr->read_finish) {
-                int err;
+        if (!snapshot) {
+                auxtrace_mmap__write_tail(mm, head);
+                if (itr->read_finish) {
+                        int err;
 
-                err = itr->read_finish(itr, mm->idx);
-                if (err < 0)
-                        return err;
+                        err = itr->read_finish(itr, mm->idx);
+                        if (err < 0)
+                                return err;
+                }
         }
 
         return 1;
 }
 
+int auxtrace_mmap__read(struct auxtrace_mmap *mm, struct auxtrace_record *itr,
+                        struct perf_tool *tool, process_auxtrace_t fn)
+{
+        return __auxtrace_mmap__read(mm, itr, tool, fn, false, 0);
+}
+
+int auxtrace_mmap__read_snapshot(struct auxtrace_mmap *mm,
+                                 struct auxtrace_record *itr,
+                                 struct perf_tool *tool, process_auxtrace_t fn,
+                                 size_t snapshot_size)
+{
+        return __auxtrace_mmap__read(mm, itr, tool, fn, true, snapshot_size);
+}
+
 /**
  * struct auxtrace_cache - hash table to implement a cache
  * @hashtable: the hashtable
diff --git a/tools/perf/util/auxtrace.h b/tools/perf/util/auxtrace.h
index 8c6cbb123fe5..c2c677e62733 100644
--- a/tools/perf/util/auxtrace.h
+++ b/tools/perf/util/auxtrace.h
@@ -276,6 +276,10 @@ struct auxtrace_mmap_params {
  * @info_priv_size: return the size of the private data in auxtrace_info_event
  * @info_fill: fill-in the private data in auxtrace_info_event
  * @free: free this auxtrace record structure
+ * @snapshot_start: starting a snapshot
+ * @snapshot_finish: finishing a snapshot
+ * @find_snapshot: find data to snapshot within auxtrace mmap
+ * @parse_snapshot_options: parse snapshot options
  * @reference: provide a 64-bit reference number for auxtrace_event
  * @read_finish: called after reading from an auxtrace mmap
  */
@@ -289,12 +293,36 @@ struct auxtrace_record {
                          struct auxtrace_info_event *auxtrace_info,
                          size_t priv_size);
         void (*free)(struct auxtrace_record *itr);
+        int (*snapshot_start)(struct auxtrace_record *itr);
+        int (*snapshot_finish)(struct auxtrace_record *itr);
+        int (*find_snapshot)(struct auxtrace_record *itr, int idx,
+                             struct auxtrace_mmap *mm, unsigned char *data,
+                             u64 *head, u64 *old);
+        int (*parse_snapshot_options)(struct auxtrace_record *itr,
+                                      struct record_opts *opts,
+                                      const char *str);
         u64 (*reference)(struct auxtrace_record *itr);
         int (*read_finish)(struct auxtrace_record *itr, int idx);
 };
 
 #ifdef HAVE_AUXTRACE_SUPPORT
 
+/*
+ * In snapshot mode the mmapped page is read-only which makes using
+ * __sync_val_compare_and_swap() problematic.  However, snapshot mode expects
+ * the buffer is not updated while the snapshot is made (e.g. Intel PT disables
+ * the event) so there is not a race anyway.
+ */
+static inline u64 auxtrace_mmap__read_snapshot_head(struct auxtrace_mmap *mm)
+{
+        struct perf_event_mmap_page *pc = mm->userpg;
+        u64 head = ACCESS_ONCE(pc->aux_head);
+
+        /* Ensure all reads are done after we read the head */
+        rmb();
+        return head;
+}
+
 static inline u64 auxtrace_mmap__read_head(struct auxtrace_mmap *mm)
 {
         struct perf_event_mmap_page *pc = mm->userpg;
@@ -346,6 +374,11 @@ typedef int (*process_auxtrace_t)(struct perf_tool *tool,
 int auxtrace_mmap__read(struct auxtrace_mmap *mm, struct auxtrace_record *itr,
                         struct perf_tool *tool, process_auxtrace_t fn);
 
+int auxtrace_mmap__read_snapshot(struct auxtrace_mmap *mm,
+                                 struct auxtrace_record *itr,
+                                 struct perf_tool *tool, process_auxtrace_t fn,
+                                 size_t snapshot_size);
+
 int auxtrace_queues__init(struct auxtrace_queues *queues);
 int auxtrace_queues__add_event(struct auxtrace_queues *queues,
                                struct perf_session *session,
@@ -383,6 +416,9 @@ void *auxtrace_cache__lookup(struct auxtrace_cache *c, u32 key);
 struct auxtrace_record *auxtrace_record__init(struct perf_evlist *evlist,
                                               int *err);
 
+int auxtrace_parse_snapshot_options(struct auxtrace_record *itr,
+                                    struct record_opts *opts,
+                                    const char *str);
 int auxtrace_record__options(struct auxtrace_record *itr,
                              struct perf_evlist *evlist,
                              struct record_opts *opts);
@@ -392,6 +428,11 @@ int auxtrace_record__info_fill(struct auxtrace_record *itr,
                                struct auxtrace_info_event *auxtrace_info,
                                size_t priv_size);
 void auxtrace_record__free(struct auxtrace_record *itr);
+int auxtrace_record__snapshot_start(struct auxtrace_record *itr);
+int auxtrace_record__snapshot_finish(struct auxtrace_record *itr);
+int auxtrace_record__find_snapshot(struct auxtrace_record *itr, int idx,
+                                   struct auxtrace_mmap *mm,
+                                   unsigned char *data, u64 *head, u64 *old);
 u64 auxtrace_record__reference(struct auxtrace_record *itr);
 
 int auxtrace_index__auxtrace_event(struct list_head *head, union perf_event *event,