Add VCHAN_DEBUG for strace debugging of vchan apps

1 files changed, 22 insertions, 0 deletions

diff --git a/vchan/io.c b/vchan/io.c
index fd538a9..6034c77 100644
--- a/vchan/io.c
+++ b/vchan/io.c
@@ -25,6 +25,10 @@
 #include <sys/ioctl.h>
 #include <unistd.h>
 
+// allow vchan data to be easily observed in strace() by doing a
+// writev() to FD -1 with the data being read/written.
+#define VCHAN_DEBUG 1
+
 static uint32_t rd_prod(struct libvchan *ctrl)
 {
 	return ctrl->read.shr->prod;
@@ -102,6 +106,15 @@ static int do_send(struct libvchan *ctrl, const void *data, size_t size)
 {
 	int real_idx = wr_prod(ctrl) & (wr_ring_size(ctrl) - 1);
 	int avail_contig = wr_ring_size(ctrl) - real_idx;
+	if (VCHAN_DEBUG) {
+		char metainfo[32];
+		struct iovec iov[2];
+		iov[0].iov_base = metainfo;
+		iov[0].iov_len = snprintf(metainfo, 32, "vchan wr %d/%d", ctrl->other_domain_id, ctrl->device_number);
+		iov[1].iov_base = data;
+		iov[1].iov_len = size;
+		writev(-1, iov, 2);
+	}
 	if (avail_contig > size)
 		avail_contig = size;
 	memcpy(wr_ring(ctrl) + real_idx, data, avail_contig);
@@ -148,6 +161,15 @@ static int do_recv(struct libvchan *ctrl, void *data, size_t size)
 		memcpy(data + avail_contig, rd_ring(ctrl), size - avail_contig);
 	}
 	rd_cons(ctrl) += size;
+	if (VCHAN_DEBUG) {
+		char metainfo[32];
+		struct iovec iov[2];
+		iov[0].iov_base = metainfo;
+		iov[0].iov_len = snprintf(metainfo, 32, "vchan rd %d/%d", ctrl->other_domain_id, ctrl->device_number);
+		iov[1].iov_base = data;
+		iov[1].iov_len = size;
+		writev(-1, iov, 2);
+	}
 	if (do_notify(ctrl) < 0)
 		return -1;
 	return size;