[PATCH] qemu vnc updates

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

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Hi all,
reading qemu code I realized that the qemu vnc server sometimes sends 
framebuffer updates even if the client didn't request any.
This is not consistent with the RFB protocol spec and can break some 
clients.
The patch I am attaching strictly enforces compliance with the RFB 
protocol making sure framebuffer updates are sent only if the client 
requested one.
Doing so is more difficult than it seems because some framebuffer 
pseudo-encoding updates cannot be discarded but must be sent anyway: for 
example desktop resize and pixel format change messages. To solve the 
problem I wrote a queue that stores those messages and sends them as 
soon as the client asks for an update.
Since 90% of the times the queue is used to store only few elements, the 
queue allocates 10 elements at the beginning and every time it runs out 
of elements allocates other 10 elements. This is should drastically 
limit the number of malloc and free needed to maintain the queue.
I did some stress tests in the last couple of days and seems to work well.
Best Regards,

Stefano Stabellini


Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

[-- Attachment #2: vnc-update.patch --]
[-- Type: text/x-patch, Size: 10984 bytes --]

diff -r d34e99141506 tools/ioemu/vnc.c
--- a/tools/ioemu/vnc.c	Mon Feb 25 16:34:49 2008 +0000
+++ b/tools/ioemu/vnc.c	Mon Feb 25 17:18:17 2008 +0000
@@ -137,6 +137,23 @@ enum {
 
 #endif /* CONFIG_VNC_TLS */
 
+#define QUEUE_ALLOC_UNIT 10
+
+typedef struct _QueueItem
+{
+    int x, y, w, h;
+    int32_t enc;
+    struct _QueueItem *next;
+} QueueItem;
+
+typedef struct _Queue
+{
+    QueueItem *queue_start;
+    int start_count;
+    QueueItem *queue_end;
+    int end_count;
+} Queue;
+
 struct VncState
 {
     QEMUTimer *timer;
@@ -152,6 +169,9 @@ struct VncState
     uint64_t *update_row;	/* outstanding updates */
     int has_update;		/* there's outstanding updates in the
 				 * visible area */
+
+    int update_requested;       /* the client requested an update */
+
     uint8_t *old_data;
     int depth; /* internal VNC frame buffer byte per pixel */
     int has_resize;
@@ -186,6 +206,9 @@ struct VncState
 
     Buffer output;
     Buffer input;
+    
+    Queue upqueue;
+
     kbd_layout_t *kbd_layout;
     /* current output mode information */
     VncWritePixels *write_pixels;
@@ -248,6 +271,11 @@ static void vnc_update_client(void *opaq
 static void vnc_update_client(void *opaque);
 static void vnc_client_read(void *opaque);
 static void framebuffer_set_updated(VncState *vs, int x, int y, int w, int h);
+static void pixel_format_message (VncState *vs);
+static void enqueue_framebuffer_update(VncState *vs, int x, int y, int w, int h, int32_t encoding);
+static void dequeue_framebuffer_update(VncState *vs);
+static int is_empty_queue(VncState *vs);
+static void free_queue(VncState *vs);
 
 #if 0
 static inline void vnc_set_bit(uint32_t *d, int k)
@@ -370,13 +398,18 @@ static void vnc_dpy_resize(DisplayState 
     ds->height = h;
     ds->linesize = w * vs->depth;
     if (vs->csock != -1 && vs->has_resize && size_changed) {
-	vnc_write_u8(vs, 0);  /* msg id */
-	vnc_write_u8(vs, 0);
-	vnc_write_u16(vs, 1); /* number of rects */
-	vnc_framebuffer_update(vs, 0, 0, ds->width, ds->height, -223);
-	vnc_flush(vs);
-	vs->width = ds->width;
-	vs->height = ds->height;
+        vs->width = ds->width;
+        vs->height = ds->height;
+        if (vs->update_requested) {
+	    vnc_write_u8(vs, 0);  /* msg id */
+	    vnc_write_u8(vs, 0);
+	    vnc_write_u16(vs, 1); /* number of rects */
+	    vnc_framebuffer_update(vs, 0, 0, ds->width, ds->height, -223);
+	    vnc_flush(vs);
+            vs->update_requested--;
+        } else {
+            enqueue_framebuffer_update(vs, 0, 0, ds->width, ds->height, -223);
+        }
     }
     vs->dirty_pixel_shift = 0;
     for (o = DIRTY_PIXEL_BITS; o < ds->width; o *= 2)
@@ -553,7 +586,8 @@ static void vnc_copy(DisplayState *ds, i
         return;
     }
 
-    if (src_x < vs->visible_x || src_y < vs->visible_y ||
+    if (!vs->update_requested ||
+        src_x < vs->visible_x || src_y < vs->visible_y ||
 	dst_x < vs->visible_x || dst_y < vs->visible_y ||
 	(src_x + w) > (vs->visible_x + vs->visible_w) ||
 	(src_y + h) > (vs->visible_y + vs->visible_h) ||
@@ -592,6 +626,7 @@ static void vnc_copy(DisplayState *ds, i
 	vnc_write_u16(vs, src_x);
 	vnc_write_u16(vs, src_y);
 	vnc_flush(vs);
+        vs->update_requested--;
     } else
 	framebuffer_set_updated(vs, dst_x, dst_y, w, h);
 }
@@ -624,8 +659,21 @@ static void _vnc_update_client(void *opa
     int maxx, maxy;
     int tile_bytes = vs->depth * DP2X(vs, 1);
 
-    if (vs->csock == -1)
+    if (!vs->update_requested || vs->csock == -1)
 	return;
+    while (!is_empty_queue(vs) && vs->update_requested) {
+        int enc = vs->upqueue.queue_end->enc; 
+        dequeue_framebuffer_update(vs);
+        switch (enc) {
+            case 0x574D5669:
+                pixel_format_message(vs);
+                break;
+            default:
+                break;
+        }
+        vs->update_requested--;
+    }
+    if (!vs->update_requested) return;
 
     now = qemu_get_clock(rt_clock);
 
@@ -717,8 +765,11 @@ static void _vnc_update_client(void *opa
     vs->output.buffer[saved_offset] = (n_rectangles >> 8) & 0xFF;
     vs->output.buffer[saved_offset + 1] = n_rectangles & 0xFF;
 
-    if (n_rectangles == 0)
+    if (n_rectangles == 0) {
+        vs->output.offset = saved_offset - 2;
 	goto backoff;
+    } else
+        vs->update_requested--;
 
     vs->has_update = 0;
     vnc_flush(vs);
@@ -735,7 +786,8 @@ static void _vnc_update_client(void *opa
     vs->timer_interval += VNC_REFRESH_INTERVAL_INC;
     if (vs->timer_interval > VNC_REFRESH_INTERVAL_MAX) {
 	vs->timer_interval = VNC_REFRESH_INTERVAL_MAX;
-	if (now - vs->last_update_time >= VNC_MAX_UPDATE_INTERVAL) {
+	if (now - vs->last_update_time >= VNC_MAX_UPDATE_INTERVAL &&
+            vs->update_requested) {
 	    /* Send a null update.  If the client is no longer
 	       interested (e.g. minimised) it'll ignore this, and we
 	       can stop scanning the buffer until it sends another
@@ -752,6 +804,7 @@ static void _vnc_update_client(void *opa
 	    send_framebuffer_update(vs, 0, 0, 1, 1);
 	    vnc_flush(vs);
 	    vs->last_update_time = now;
+            vs->update_requested--;
 	    return;
 	}
     }
@@ -821,6 +874,88 @@ static void buffer_append(Buffer *buffer
     buffer->offset += len;
 }
 
+static void enqueue_framebuffer_update(VncState *vs, int x, int y, int w, int h,
+                                   int32_t encoding)
+{
+    Queue *q = &vs->upqueue; 
+    if (q->queue_end != NULL) {
+        if (q->queue_end != q->queue_start || q->start_count != q->end_count) {
+            if (q->queue_end->next == NULL) {
+                q->queue_end->next = (QueueItem *) qemu_mallocz (sizeof(QueueItem) * QUEUE_ALLOC_UNIT);
+                q->end_count = QUEUE_ALLOC_UNIT;
+            }
+            q->queue_end = q->queue_end->next;
+        }
+    } else {
+        q->queue_end = (QueueItem *) qemu_mallocz (sizeof(QueueItem) * QUEUE_ALLOC_UNIT);
+        q->queue_start = q->queue_end;
+        q->start_count = QUEUE_ALLOC_UNIT;
+        q->end_count = QUEUE_ALLOC_UNIT;
+    }
+    q->end_count--;
+
+    q->queue_end->x = x;
+    q->queue_end->y = y;
+    q->queue_end->w = w;
+    q->queue_end->h = h;
+    q->queue_end->enc = encoding;
+    q->queue_end->next = (q->end_count > 0) ? (q->queue_end + 1) : NULL;
+}
+
+static void dequeue_framebuffer_update(VncState *vs)
+{
+    Queue *q = &vs->upqueue;
+    if (q->queue_start == NULL || 
+            (q->queue_end == q->queue_start && q->start_count == q->end_count))
+        return;
+
+    vnc_write_u8(vs, 0);
+    vnc_write_u8(vs, 0);
+    vnc_write_u16(vs, 1);
+    vnc_framebuffer_update(vs, q->queue_start->x, q->queue_start->y,
+            q->queue_start->w, q->queue_start->h, q->queue_start->enc);
+
+    q->start_count--;
+    if (q->queue_end != q->queue_start) {
+        if (!q->start_count) {
+            QueueItem *i = q->queue_start;
+            q->queue_start = q->queue_start->next;
+            q->start_count = QUEUE_ALLOC_UNIT;
+            free (i - QUEUE_ALLOC_UNIT + 1);
+        } else
+            q->queue_start = q->queue_start->next;
+    } else {
+        q->queue_end = q->queue_end - QUEUE_ALLOC_UNIT + q->end_count + 1;
+        q->queue_start = q->queue_end;
+        q->end_count = QUEUE_ALLOC_UNIT;
+        q->start_count = QUEUE_ALLOC_UNIT;
+    }
+}
+
+static int is_empty_queue(VncState *vs)
+{
+    Queue *q = &vs->upqueue;
+    if (q->queue_end == NULL) return 1;
+    if (q->queue_end == q->queue_start && q->start_count == q->end_count) return 1;
+    return 0;
+}
+
+static void free_queue(VncState *vs)
+{
+    Queue *q = &vs->upqueue;
+    while (q->queue_start != NULL) {
+        QueueItem *i;
+        q->queue_start = q->queue_start + q->start_count - 1;
+        i = q->queue_start;
+        q->queue_start = q->queue_start->next;
+        free(i - QUEUE_ALLOC_UNIT + 1);
+        q->start_count = QUEUE_ALLOC_UNIT;
+    }
+    q->queue_end = NULL;
+    q->start_count = 0;
+    q->end_count = 0;
+}
+
 static int vnc_client_io_error(VncState *vs, int ret, int last_errno)
 {
     if (ret == 0 || ret == -1) {
@@ -833,6 +968,8 @@ static int vnc_client_io_error(VncState 
 	vs->csock = -1;
 	buffer_reset(&vs->input);
 	buffer_reset(&vs->output);
+        free_queue(vs);
+        vs->update_requested = 0;
 #if CONFIG_VNC_TLS
 	if (vs->tls_session) {
 	    gnutls_deinit(vs->tls_session);
@@ -1044,12 +1181,18 @@ static void check_pointer_type_change(Vn
 static void check_pointer_type_change(VncState *vs, int absolute)
 {
     if (vs->has_pointer_type_change && vs->absolute != absolute) {
-	vnc_write_u8(vs, 0);
-	vnc_write_u8(vs, 0);
-	vnc_write_u16(vs, 1);
-	vnc_framebuffer_update(vs, absolute, 0,
+        if (vs->update_requested) {
+	    vnc_write_u8(vs, 0);
+	    vnc_write_u8(vs, 0);
+	    vnc_write_u16(vs, 1);
+	    vnc_framebuffer_update(vs, absolute, 0,
 			       vs->ds->width, vs->ds->height, -257);
-	vnc_flush(vs);
+	    vnc_flush(vs);
+            vs->update_requested--;
+        } else {
+            enqueue_framebuffer_update(vs, absolute, 0,
+                               vs->ds->width, vs->ds->height, -257);
+        }
     }
     vs->absolute = absolute;
 }
@@ -1316,6 +1459,7 @@ static void framebuffer_update_request(V
     vs->visible_w = w;
     vs->visible_h = h;
 
+    vs->update_requested++;
     qemu_mod_timer(vs->timer, qemu_get_clock(rt_clock));
 }
 
@@ -1536,12 +1680,17 @@ static void vnc_dpy_colourdepth(DisplayS
         vnc_client_error(vs);
     } else if (vs->csock != -1 && vs->has_WMVi) {
         /* Sending a WMVi message to notify the client*/
-        vnc_write_u8(vs, 0);  /* msg id */
-        vnc_write_u8(vs, 0);
-        vnc_write_u16(vs, 1); /* number of rects */
-        vnc_framebuffer_update(vs, 0, 0, ds->width, ds->height, 0x574D5669);
-        pixel_format_message(vs);
-        vnc_flush(vs);
+        if (vs->update_requested) {
+            vnc_write_u8(vs, 0);  /* msg id */
+            vnc_write_u8(vs, 0);
+            vnc_write_u16(vs, 1); /* number of rects */
+            vnc_framebuffer_update(vs, 0, 0, ds->width, ds->height, 0x574D5669);
+            pixel_format_message(vs);
+            vnc_flush(vs);
+            vs->update_requested--;
+        } else {
+            enqueue_framebuffer_update(vs, 0, 0, ds->width, ds->height, 0x574D5669);
+        }
     } else {
         if (vs->pix_bpp == 4 && vs->depth == 4 &&
             host_big_endian_flag == vs->pix_big_endian &&
@@ -2291,6 +2440,7 @@ static void vnc_listen_read(void *opaque
 	framebuffer_set_updated(vs, 0, 0, vs->ds->width, vs->ds->height);
 	vs->has_resize = 0;
 	vs->has_hextile = 0;
+        vs->update_requested = 0;
 	vs->ds->dpy_copy = NULL;
 	vnc_timer_init(vs);
     }
@@ -2413,6 +2563,8 @@ void vnc_display_close(DisplayState *ds)
 	vs->csock = -1;
 	buffer_reset(&vs->input);
 	buffer_reset(&vs->output);
+        free_queue(vs);
+        vs->update_requested = 0;
 #if CONFIG_VNC_TLS
 	if (vs->tls_session) {
 	    gnutls_deinit(vs->tls_session);

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