char_device: Introducing shared flow control code for char devices.

SpiceCharDeviceState manages the (1) write-to-device queue
(2) wakeup and reading from the device (3) client tokens (4)
sending messages from the device to the client/s, considering the
available tokens.
SpiceCharDeviceState can be also stopped and started. When the device
is stopped, no reading or writing is done from/to the device. Messages
addressed from the client to the device are being queued.
Later, an api for stop/start will be added to spice.h and it should
be called from qemu.

This patch does not yet remove the wakeup callback from
SpiceCharDeviceState, but once all the char devices (agent/spicevmc/smartcard)
code will switch to the new implementation, SpiceCharDeviceState
will be moved to the c file and its reference to the wakeup callback will be removed.

1 files changed, 201 insertions, 0 deletions

diff --git a/server/char_device.h b/server/char_device.h
index bdb32ae9..db27bece 100644
--- a/server/char_device.h
+++ b/server/char_device.h
@@ -2,11 +2,212 @@
 #define __CHAR_DEVICE_H__
 
 #include "spice.h"
+#include "red_channel.h"
+
+/*
+ * Shared code for char devices, mainly for flow control.
+ *
+ * How to use the api:
+ * ==================
+ * device attached: call spice_char_device_state_create
+ * device detached: call spice_char_device_state_destroy/reset
+ *
+ * client connected and assoicated with a device: spice_char_device_client_add
+ * client disconnected: spice_char_device_client_remove
+ *
+ * Writing to the device
+ * ---------------------
+ * Write the data into SpiceCharDeviceWriteBuffer:
+ * call spice_char_device_write_buffer_get in order to get an appropriate buffer.
+ * call spice_char_device_write_buffer_add in order to push the buffer to the write queue.
+ * If you choose not to push the buffer to the device, call
+ * spice_char_device_write_buffer_release
+ *
+ * reading from the device
+ * -----------------------
+ *  The callback read_one_msg_from_device (see below) should be implemented
+ *  (using sif->read).
+ *  When the device is ready, this callback is called, and is expected to
+ *  return one message which is addressed to the client, or NULL if the read
+ *  hasn't completed.
+ *
+ * calls triggered from the device (qemu):
+ * --------------------------------------
+ * spice_char_device_start
+ * spice_char_device_stop
+ * spice_char_device_wakeup (for reading from the device)
+ */
+
+/*
+ * Note about multiple-clients:
+ * Multiclients are currently not supported in any of the character devices:
+ * spicevmc does not allow more than one client (and at least for usb, it should stay this way).
+ * smartcard code is not compatible with more than one reader.
+ * The server and guest agent code doesn't distinguish messages from different clients.
+ * In addition, its current flow control code (e.g., tokens handling) is wrong and doesn't
+ * take into account the different clients.
+ *
+ * Nonetheless, the following code introduces some support for multiple-clients:
+ * We track the number of tokens for all the clients, and we read from the device
+ * if one of the clients have enough tokens. For the clients that don't have tokens,
+ * we queue the messages, till they receive tokens, or till a timeout.
+ *
+ * TODO:
+ * At least for the agent, not all the messages from the device will be directed to all
+ * the clients (e.g., copy from guest to a specific client). Thus, support for
+ * client-specific-messages should be added.
+ * In addition, we should have support for clients that are being connected
+ * in the middle of a message transfer from the agent to the clients.
+ *
+ * */
+
+/* buffer that is used for writing to the device */
+typedef struct SpiceCharDeviceWriteBuffer {
+    RingItem link;
+    int origin;
+    RedClient *client; /* The client that sent the message to the device.
+                          NULL if the server created the message */
+
+    uint8_t *buf;
+    uint32_t buf_size;
+    uint32_t buf_used;
+} SpiceCharDeviceWriteBuffer;
+
+typedef void SpiceCharDeviceMsgToClient;
+
+typedef struct SpiceCharDeviceCallbacks {
+    /*
+     * Messages that are addressed to the client can be queued in case we have
+     * multiple clients and some of them don't have enough tokens.
+     */
+
+    /* reads from the device till reaching a msg that should be sent to the client,
+     * or till the reading fails */
+    SpiceCharDeviceMsgToClient* (*read_one_msg_from_device)(SpiceCharDeviceInstance *sin,
+                                                            void *opaque);
+    SpiceCharDeviceMsgToClient* (*ref_msg_to_client)(SpiceCharDeviceMsgToClient *msg,
+                                                     void *opaque);
+    void (*unref_msg_to_client)(SpiceCharDeviceMsgToClient *msg,
+                                void *opaque);
+    void (*send_msg_to_client)(SpiceCharDeviceMsgToClient *msg,
+                               RedClient *client,
+                               void *opaque); /* after this call, the message is unreferenced */
+
+    /* The cb is called when a predefined number of write buffers were consumed by the
+     * device */
+    void (*send_tokens_to_client)(RedClient *client, uint32_t tokens, void *opaque);
+
+    /* The cb is called when a server (self) message that was addressed to the device,
+     * has been completely written to it */
+    void (*on_free_self_token)(void *opaque);
+
+    /* This cb is called if it is recommanded that a client will be removed
+     * due to slow flow or due to some other error.
+     * The called instance should disconnect the client, or at least the corresponding channel */
+    void (*remove_client)(RedClient *client, void *opaque);
+} SpiceCharDeviceCallbacks;
+
+typedef struct SpiceCharDeviceState SpiceCharDeviceState;
 
 struct SpiceCharDeviceState {
+    int running;
+    uint32_t refs;
+
+    Ring write_queue;
+    Ring write_bufs_pool;
+    SpiceCharDeviceWriteBuffer *cur_write_buf;
+    uint8_t *cur_write_buf_pos;
+    SpiceTimer *write_to_dev_timer;
+    uint64_t num_self_tokens;
+
+    Ring clients;
+    uint32_t num_clients;
+
+    uint64_t client_tokens_interval; /* frequency of returning tokens to the client */
+    SpiceCharDeviceInstance *sin;
+
+    int during_read_from_device;
+
+    SpiceCharDeviceCallbacks cbs;
+    void *opaque;
+    /* tmp till all spice char devices will employ the new SpiceCharDeviceState
+     * implementation. Then, SpiceCharDeviceState will be moved to char_device.c and
+     * this callback will be removed */
     void (*wakeup)(SpiceCharDeviceInstance *sin);
 };
 
+
+SpiceCharDeviceState *spice_char_device_state_create(SpiceCharDeviceInstance *sin,
+                                                     uint32_t client_tokens_interval,
+                                                     uint32_t self_tokens,
+                                                     SpiceCharDeviceCallbacks *cbs,
+                                                     void *opaque);
+
+void spice_char_device_state_reset_dev_instance(SpiceCharDeviceState *dev,
+                                                SpiceCharDeviceInstance *sin);
+void spice_char_device_state_destroy(SpiceCharDeviceState *dev);
+
+void *spice_char_device_state_opaque_get(SpiceCharDeviceState *dev);
+
+
+/*
+ * Resets write/read queues, and moves that state to being stopped.
+ * This routine is a workaround for a bad tokens management in the vdagent
+ * protocol:
+ *  The client tokens' are set only once, when the main channel is initialized.
+ *  Instead, it would have been more appropriate to reset them upon AGEN_CONNECT.
+ *  The client tokens are tracked as part of the SpiceCharDeviceClientState. Thus,
+ *  in order to be backwartd compatible with the client, we need to track the tokens
+ *  event when the agent is detached. We don't destroy the the char_device state, and
+ *  instead we just reset it.
+ *  In addition, there is a misshandling of AGENT_TOKENS message in spice-gtk: it
+ *  overrides the amount of tokens, instead of adding the given amount.
+ *
+ *  todo: change AGENT_CONNECT msg to contain tokens count.
+ */
+void spice_char_device_reset(SpiceCharDeviceState *dev);
+
+/* max_send_queue_size = how many messages we can read from the device and enqueue for this client,
+ * when we have tokens for other clients and no tokens for this one */
+void spice_char_device_client_add(SpiceCharDeviceState *dev,
+                                  RedClient *client,
+                                  int do_flow_control,
+                                  uint32_t max_send_queue_size,
+                                  uint32_t num_client_tokens,
+                                  uint32_t num_send_tokens);
+
+void spice_char_device_client_remove(SpiceCharDeviceState *dev,
+                                     RedClient *client);
+int spice_char_device_client_exists(SpiceCharDeviceState *dev,
+                                    RedClient *client);
+
+void spice_char_device_start(SpiceCharDeviceState *dev);
+void spice_char_device_stop(SpiceCharDeviceState *dev);
+
+/** Read from device **/
+
+void spice_char_device_wakeup(SpiceCharDeviceState *dev);
+
+void spice_char_device_send_to_client_tokens_add(SpiceCharDeviceState *dev,
+                                                 RedClient *client,
+                                                 uint32_t tokens);
+
+
+void spice_char_device_send_to_client_tokens_set(SpiceCharDeviceState *dev,
+                                                 RedClient *client,
+                                                 uint32_t tokens);
+/** Write to device **/
+
+SpiceCharDeviceWriteBuffer *spice_char_device_write_buffer_get(SpiceCharDeviceState *dev,
+                                                               RedClient *client, int size);
+/* Either add the buffer to the write queue or release it */
+void spice_char_device_write_buffer_add(SpiceCharDeviceState *dev,
+                                        SpiceCharDeviceWriteBuffer *write_buf);
+void spice_char_device_write_buffer_release(SpiceCharDeviceState *dev,
+                                            SpiceCharDeviceWriteBuffer *write_buf);
+
+/* api for specific char devices */
+
 void spicevmc_device_connect(SpiceCharDeviceInstance *sin,
                              uint8_t channel_type);
 void spicevmc_device_disconnect(SpiceCharDeviceInstance *char_device);