[2/4] power: extend guest channel api for reading

diff --git a/lib/librte_power/channel_commands.h b/lib/librte_power/channel_commands.h
index e7b93a797..1aff604c4 100644
--- a/lib/librte_power/channel_commands.h
+++ b/lib/librte_power/channel_commands.h
@@ -28,6 +28,11 @@  extern "C" {
 #define CPU_POWER_SCALE_MIN     4
 #define CPU_POWER_ENABLE_TURBO  5
 #define CPU_POWER_DISABLE_TURBO 6
+
+/* Generic Power Command Response */
+#define CPU_POWER_CMD_ACK       1
+#define CPU_POWER_CMD_NAK       2
+
 #define HOURS 24
 
 #define MAX_VFS 10
diff --git a/lib/librte_power/guest_channel.c b/lib/librte_power/guest_channel.c
index 9cf7d2cb2..3fc0abfcc 100644
--- a/lib/librte_power/guest_channel.c
+++ b/lib/librte_power/guest_channel.c
@@ -10,6 +10,7 @@ 
 #include <fcntl.h>
 #include <string.h>
 #include <errno.h>
+#include <poll.h>
 
 
 #include <rte_log.h>
@@ -19,6 +20,9 @@ 
 
 #define RTE_LOGTYPE_GUEST_CHANNEL RTE_LOGTYPE_USER1
 
+/* Timeout for incoming message in milliseconds. */
+#define TIMEOUT 10
+
 static int global_fds[RTE_MAX_LCORE] = { [0 ... RTE_MAX_LCORE-1] = -1 };
 
 int
@@ -125,6 +129,59 @@  int rte_power_guest_channel_send_msg(struct channel_packet *pkt,
 	return guest_channel_send_msg(pkt, lcore_id);
 }
 
+int power_guest_channel_read_msg(struct channel_packet *pkt,
+			unsigned int lcore_id)
+{
+	int ret, buffer_len = sizeof(*pkt);
+	void *buffer = pkt;
+
+	if (lcore_id >= RTE_MAX_LCORE) {
+		RTE_LOG(ERR, GUEST_CHANNEL, "Channel(%u) is out of range 0...%d\n",
+				lcore_id, RTE_MAX_LCORE-1);
+		return -1;
+	}
+
+	if (global_fds[lcore_id] == 0) {
+		RTE_LOG(ERR, GUEST_CHANNEL, "Channel is not connected\n");
+		return -1;
+	}
+
+	while (buffer_len > 0) {
+		ret = read(global_fds[lcore_id],
+				buffer, buffer_len);
+		if (ret < 0) {
+			if (errno == EINTR)
+				continue;
+			return -1;
+		}
+		buffer = (char *)buffer + ret;
+		buffer_len -= ret;
+	}
+
+	return 0;
+}
+
+int rte_power_guest_channel_receive_msg(struct channel_packet *pkt,
+			unsigned int lcore_id)
+{
+	int ret;
+
+	struct pollfd fds;
+	fds.fd = global_fds[lcore_id];
+	fds.events = POLLIN;
+
+	ret = poll(&fds, 1, TIMEOUT);
+	if (ret == 0) {
+		RTE_LOG(DEBUG, GUEST_CHANNEL, "Timeout occurs during poll function.\n");
+		return -1;
+	} else if (ret < 0) {
+		RTE_LOG(ERR, GUEST_CHANNEL, "Error occured during poll function: %s\n",
+				strerror(ret));
+		return -1;
+	}
+
+	return power_guest_channel_read_msg(pkt, lcore_id);
+}
 
 void
 guest_channel_host_disconnect(unsigned int lcore_id)
diff --git a/lib/librte_power/guest_channel.h b/lib/librte_power/guest_channel.h
index 373d39898..7c385df39 100644
--- a/lib/librte_power/guest_channel.h
+++ b/lib/librte_power/guest_channel.h
@@ -68,6 +68,41 @@  int guest_channel_send_msg(struct channel_packet *pkt, unsigned int lcore_id);
 int rte_power_guest_channel_send_msg(struct channel_packet *pkt,
 			unsigned int lcore_id);
 
+/**
+ * Read a message contained in pkt over the Virtio-Serial
+ * from the host endpoint.
+ *
+ * @param pkt
+ *  Pointer to a populated struct channel_packet
+ *
+ * @param lcore_id
+ *  lcore_id.
+ *
+ * @return
+ *  - 0 on success.
+ *  - Negative on error.
+ */
+int power_guest_channel_read_msg(struct channel_packet *pkt,
+		unsigned int lcore_id);
+
+/**
+ * Receive a message contained in pkt over the Virtio-Serial
+ * from the host endpoint.
+ *
+ * @param pkt
+ *  Pointer to a populated struct channel_packet
+ *
+ * @param lcore_id
+ *  lcore_id.
+ *
+ * @return
+ *  - 0 on success.
+ *  - Negative on error.
+ */
+int __rte_experimental
+rte_power_guest_channel_receive_msg(struct channel_packet *pkt,
+			unsigned int lcore_id);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/lib/librte_power/rte_power_version.map b/lib/librte_power/rte_power_version.map
index 042917360..69f5ea3f4 100644
--- a/lib/librte_power/rte_power_version.map
+++ b/lib/librte_power/rte_power_version.map
@@ -44,4 +44,5 @@  EXPERIMENTAL {
 	rte_power_empty_poll_stat_update;
 	rte_power_poll_stat_fetch;
 	rte_power_poll_stat_update;
+	rte_power_guest_channel_receive_msg;
 };