Calculate context length outside of retry loop

[lttng-modules.git] / lib / ringbuffer / ring_buffer_frontend.c

diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index 68b62382e9fc87c2a307887cc67e144dfe1528a8..310752506550bda15e03d6d57eff5d5f7a43398c 100644 (file)
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -1119,6 +1119,37 @@ nodata:
 }
 EXPORT_SYMBOL_GPL(lib_ring_buffer_snapshot);
 
+/**
+ * Performs the same function as lib_ring_buffer_snapshot(), but the positions
+ * are saved regardless of whether the consumed and produced positions are
+ * in the same subbuffer.
+ * @buf: ring buffer
+ * @consumed: consumed byte count indicating the last position read
+ * @produced: produced byte count indicating the last position written
+ *
+ * This function is meant to provide information on the exact producer and
+ * consumer positions without regard for the "snapshot" feature.
+ */
+int lib_ring_buffer_snapshot_sample_positions(struct lib_ring_buffer *buf,
+               unsigned long *consumed, unsigned long *produced)
+{
+       struct channel *chan = buf->backend.chan;
+       const struct lib_ring_buffer_config *config = &chan->backend.config;
+
+       smp_rmb();
+       *consumed = atomic_long_read(&buf->consumed);
+       /*
+        * No need to issue a memory barrier between consumed count read and
+        * write offset read, because consumed count can only change
+        * concurrently in overwrite mode, and we keep a sequence counter
+        * identifier derived from the write offset to check we are getting
+        * the same sub-buffer we are expecting (the sub-buffers are atomically
+        * "tagged" upon writes, tags are checked upon read).
+        */
+       *produced = v_read(config, &buf->offset);
+       return 0;
+}
+
 /**
  * lib_ring_buffer_put_snapshot - move consumed counter forward
  *
@@ -1464,8 +1495,7 @@ void lib_ring_buffer_print_errors(struct channel *chan,
 /*
  * lib_ring_buffer_switch_old_start: Populate old subbuffer header.
  *
- * Only executed by SWITCH_FLUSH, which can be issued while tracing is active
- * or at buffer finalization (destroy).
+ * Only executed when the buffer is finalized, in SWITCH_FLUSH.
  */
 static
 void lib_ring_buffer_switch_old_start(struct lib_ring_buffer *buf,
@@ -1661,14 +1691,12 @@ int lib_ring_buffer_try_switch_slow(enum switch_mode mode,
                unsigned long sb_index, commit_count;
 
                /*
-                * We are performing a SWITCH_FLUSH. There may be concurrent
-                * writes into the buffer if e.g. invoked while performing a
-                * snapshot on an active trace.
+                * We are performing a SWITCH_FLUSH. At this stage, there are no
+                * concurrent writes into the buffer.
                 *
-                * If the client does not save any header information (sub-buffer
-                * header size == 0), don't switch empty subbuffer on finalize,
-                * because it is invalid to deliver a completely empty
-                * subbuffer.
+                * The client does not save any header information.  Don't
+                * switch empty subbuffer on finalize, because it is invalid to
+                * deliver a completely empty subbuffer.
                 */
                if (!config->cb.subbuffer_header_size())
                        return -1;
@@ -1833,6 +1861,7 @@ static void _lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf,
        put_online_cpus();
 }
 
+/* Switch sub-buffer if current sub-buffer is non-empty. */
 void lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf)
 {
        _lib_ring_buffer_switch_remote(buf, SWITCH_ACTIVE);
@@ -1857,7 +1886,8 @@ static
 int lib_ring_buffer_try_reserve_slow(struct lib_ring_buffer *buf,
                                     struct channel *chan,
                                     struct switch_offsets *offsets,
-                                    struct lib_ring_buffer_ctx *ctx)
+                                    struct lib_ring_buffer_ctx *ctx,
+                                    void *client_ctx)
 {
        const struct lib_ring_buffer_config *config = &chan->backend.config;
        unsigned long reserve_commit_diff, offset_cmp;
@@ -1883,7 +1913,7 @@ retry:
                offsets->size = config->cb.record_header_size(config, chan,
                                                offsets->begin,
                                                &offsets->pre_header_padding,
-                                               ctx);
+                                               ctx, client_ctx);
                offsets->size +=
                        lib_ring_buffer_align(offsets->begin + offsets->size,
                                              ctx->largest_align)
@@ -1967,7 +1997,7 @@ retry:
                        config->cb.record_header_size(config, chan,
                                                offsets->begin,
                                                &offsets->pre_header_padding,
-                                               ctx);
+                                               ctx, client_ctx);
                offsets->size +=
                        lib_ring_buffer_align(offsets->begin + offsets->size,
                                              ctx->largest_align)
@@ -2031,7 +2061,8 @@ EXPORT_SYMBOL_GPL(lib_ring_buffer_lost_event_too_big);
  * -EIO for other errors, else returns 0.
  * It will take care of sub-buffer switching.
  */
-int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx *ctx)
+int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx *ctx,
+               void *client_ctx)
 {
        struct channel *chan = ctx->chan;
        const struct lib_ring_buffer_config *config = &chan->backend.config;
@@ -2044,7 +2075,7 @@ int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx *ctx)
 
        do {
                ret = lib_ring_buffer_try_reserve_slow(buf, chan, &offsets,
-                                                      ctx);
+                                                      ctx, client_ctx);
                if (unlikely(ret))
                        return ret;
        } while (unlikely(v_cmpxchg(config, &buf->offset, offsets.old,