trace-cmd: Add blktrace_api compatibility for TC_BARRIER

Newer kernels replace TC_BARRIER with TC_FLUSH. Ensure trace-cmd
can build regardless of the linux-kernel-headers version.

Upstream-Status: Innapropriate [Stop gap]

Signed-off-by: Darren Hart <dvhart@linux.intel.com>

diff --git a/plugin_blk.c b/plugin_blk.c
index 9327b17..c8e5e1c 100644
--- a/plugin_blk.c
+++ b/plugin_blk.c
@@ -44,6 +44,15 @@ struct blk_data {
 	unsigned short		pdu_len;
 };
 
+/*
+ * Newer kernels don't define BLK_TC_BARRIER and have replaced it with
+ * BLK_TC_FLUSH. In this case, define it here and report FLUSHES as BARRIERS as
+ * a workaround, as described in:
+ * http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commit;h=c09c47caedc9854d59378d6e34c989e51cfdd2b4
+ */
+#ifndef BLK_TC_BARRIER
+#define BLK_TC_BARRIER 1<<2
+#endif
 static void fill_rwbs(char *rwbs, int action, unsigned int bytes)
 {
 	int i = 0;