X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=include%2Flttng%2Fringbuffer-config.h;h=c95d35cb348d820e69adba599ad3f90b9583b130;hb=82cd0cfd74e2e7fe71d9ff68a9e521d989f72d99;hp=5ae0d8a6a4985500e168ab0e529b8642f0cba554;hpb=15500a1bb134d6bbd409da5568308c2a41291928;p=lttng-ust.git

diff --git a/include/lttng/ringbuffer-config.h b/include/lttng/ringbuffer-config.h
index 5ae0d8a6..c95d35cb 100644
--- a/include/lttng/ringbuffer-config.h
+++ b/include/lttng/ringbuffer-config.h
@@ -256,10 +256,21 @@ struct lttng_ust_lib_ring_buffer_ctx {
 					 */
 	uint64_t tsc;			/* time-stamp counter value */
 	unsigned int rflags;		/* reservation flags */
-	unsigned int padding1;		/* padding to realign on pointer */
+	/*
+	 * The field ctx_len is the length of struct
+	 * lttng_ust_lib_ring_buffer_ctx as known by the user of
+	 * lib_ring_buffer_ctx_init.
+	 */
+	unsigned int ctx_len;
 	void *ip;			/* caller ip address */
 	void *priv2;			/* 2nd priv data */
 	char padding2[LTTNG_UST_RING_BUFFER_CTX_PADDING];
+	/*
+	 * This is the end of the initial fields expected by the original ABI
+	 * between probes and UST. Only the fields above can be used if
+	 * ctx_len is 0. Use the value of ctx_len to find out which of the
+	 * following fields may be used.
+	 */
 };
 
 /**
@@ -291,7 +302,7 @@ void lib_ring_buffer_ctx_init(struct lttng_ust_lib_ring_buffer_ctx *ctx,
 	ctx->cpu = cpu;
 	ctx->rflags = 0;
 	ctx->handle = handle;
-	ctx->padding1 = 0;
+	ctx->ctx_len = sizeof(struct lttng_ust_lib_ring_buffer_ctx);
 	ctx->ip = 0;
 	ctx->priv2 = priv2;
 	memset(ctx->padding2, 0, LTTNG_UST_RING_BUFFER_CTX_PADDING);