X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=libringbuffer%2Fring_buffer_frontend.c;h=76d6ec746c40ade48905bcfbf0cd3c81274d812e;hb=2df586a6d8136c08cf5f0b1210a268d6c37601de;hp=6dd81e14b0bbb6e767b44687d725c210b43661fc;hpb=932b85faaf5e3b8e164aab1247c498a94c77060f;p=lttng-ust.git

diff --git a/libringbuffer/ring_buffer_frontend.c b/libringbuffer/ring_buffer_frontend.c
index 6dd81e14..76d6ec74 100644
--- a/libringbuffer/ring_buffer_frontend.c
+++ b/libringbuffer/ring_buffer_frontend.c
@@ -1305,6 +1305,43 @@ nodata:
 		return -EAGAIN;
 }
 
+/**
+ * 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 lttng_ust_lib_ring_buffer *buf,
+			     unsigned long *consumed, unsigned long *produced,
+			     struct lttng_ust_shm_handle *handle)
+{
+	struct channel *chan;
+	const struct lttng_ust_lib_ring_buffer_config *config;
+
+	chan = shmp(handle, buf->backend.chan);
+	if (!chan)
+		return -EPERM;
+	config = &chan->backend.config;
+	cmm_smp_rmb();
+	*consumed = uatomic_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_move_consumer - move consumed counter forward
  * @buf: ring buffer
@@ -2023,7 +2060,8 @@ static
 int lib_ring_buffer_try_reserve_slow(struct lttng_ust_lib_ring_buffer *buf,
 				     struct channel *chan,
 				     struct switch_offsets *offsets,
-				     struct lttng_ust_lib_ring_buffer_ctx *ctx)
+				     struct lttng_ust_lib_ring_buffer_ctx *ctx,
+				     void *client_ctx)
 {
 	const struct lttng_ust_lib_ring_buffer_config *config = &chan->backend.config;
 	struct lttng_ust_shm_handle *handle = ctx->handle;
@@ -2051,7 +2089,7 @@ 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)
@@ -2157,7 +2195,7 @@ 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)
@@ -2211,7 +2249,8 @@ retry:
  * -EIO for other errors, else returns 0.
  * It will take care of sub-buffer switching.
  */
-int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx *ctx)
+int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx *ctx,
+		void *client_ctx)
 {
 	struct channel *chan = ctx->chan;
 	struct lttng_ust_shm_handle *handle = ctx->handle;
@@ -2232,7 +2271,7 @@ int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx *ctx)
 
 	do {
 		ret = lib_ring_buffer_try_reserve_slow(buf, chan, &offsets,
-						       ctx);
+						       ctx, client_ctx);
 		if (caa_unlikely(ret))
 			return ret;
 	} while (caa_unlikely(v_cmpxchg(config, &buf->offset, offsets.old,