>From 861be2ff3c860e180db90f7f6928fbb427d7971a Mon Sep 17 00:00:00 2001
From: Alon Levy <alevy@redhat.com>
Date: Sun, 13 Mar 2011 21:58:24 +0200
Subject: [PATCH 4/6] qxl vga update: don't read, preventing pipe loop of death

---
 hw/qxl.c           |   44 +++++++++++++++++++++++++-------------------
 ui/spice-display.h |    1 +
 2 files changed, 26 insertions(+), 19 deletions(-)

diff --git a/hw/qxl.c b/hw/qxl.c
index d040bee..dfbb740 100644
--- a/hw/qxl.c
+++ b/hw/qxl.c
@@ -356,7 +356,7 @@ static int interface_get_command(QXLInstance *sin, struct QXLCommandExt *ext)
     QXLCommand *cmd;
     int notify;
     int r;
-    unsigned char req, ack;
+    unsigned char req;
 
     switch (qxl->mode) {
     case QXL_MODE_VGA:
@@ -364,21 +364,21 @@ static int interface_get_command(QXLInstance *sin, struct QXLCommandExt *ext)
 
         /* TODO -- 1. check write+read return codes. retry upon e.g. EINTR */
         /* TODO -- 2. change the imlpementation inside qemu_spice_create_update (option rename+add functions) */
-        req = QXL_SERVER_CREATE_UPDATE;
-        r = write(qxl->pipe[1], &req , 1);
-        ASSERT(r == 1);
-        ack = 0;
-        r = read(qxl->pipe_out[0], &ack, 1);
-        ASSERT(r == 1);
-        ASSERT(ack == QXL_SERVER_CREATE_UPDATE); // ack==req
         update = qxl->ssd.update;
-        //update = qemu_spice_create_update(&qxl->ssd);
-        if (update == NULL) {
+        if (update != NULL) {
+            qxl->ssd.update = NULL;
+            *ext = update->ext;
+            qxl_log_command(qxl, "vga", ext);
+            return true;
+        } else {
+            if (!qxl->ssd.waiting_for_update) {
+                qxl->ssd.waiting_for_update = 1;
+                req = QXL_SERVER_CREATE_UPDATE;
+                r = write(qxl->pipe[1], &req , 1);
+                ASSERT(r == 1);
+            }
             return false;
         }
-        *ext = update->ext;
-        qxl_log_command(qxl, "vga", ext);
-        return true;
     case QXL_MODE_COMPAT:
     case QXL_MODE_NATIVE:
     case QXL_MODE_UNDEFINED:
@@ -611,6 +611,7 @@ static void qxl_enter_vga_mode(PCIQXLDevice *d)
     qemu_spice_create_host_primary(&d->ssd);
     d->mode = QXL_MODE_VGA;
     memset(&d->ssd.dirty, 0, sizeof(d->ssd.dirty));
+    d->ssd.waiting_for_update = 0;
 }
 
 static void qxl_exit_vga_mode(PCIQXLDevice *d)
@@ -1084,6 +1085,7 @@ static void pipe_read(void *opaque)
     PCIQXLDevice *d = opaque;
     unsigned char cmd;
     int len, again = 1, set_irq_done = 0;
+    int create_update = 0;
 
     do {
         cmd = 0;
@@ -1091,6 +1093,9 @@ static void pipe_read(void *opaque)
         if ((len < 0) && (errno == EINTR)) {
             continue;
         }
+        if (len <= 0) {
+            break;
+        }
         switch (cmd) {
         case QXL_SERVER_SET_IRQ:
             if (set_irq_done == 0) {
@@ -1100,16 +1105,19 @@ static void pipe_read(void *opaque)
             }
             break;
         case QXL_SERVER_CREATE_UPDATE:
-            again = 0;
-            d->ssd.update = qemu_spice_create_update(&d->ssd);
-            len = write(d->pipe_out[1], &cmd, 1);
-            ASSERT(len == 1);
+            create_update = 1;
             break;
         default:
             fprintf(stderr, "%s: unknown cmd %u\n", __FUNCTION__, cmd);
             abort();
         }
     } while (again);
+    if (create_update) {
+        if (d->ssd.update == NULL) {
+            d->ssd.update = qemu_spice_create_update(&d->ssd);
+        }
+        d->ssd.waiting_for_update = 0;
+    }
 }
 
 static void qxl_send_events(PCIQXLDevice *d, uint32_t events)
@@ -1145,14 +1153,12 @@ static void init_pipe_signaling(PCIQXLDevice *d)
        return;
    }
 
-#if 0 // why non-blocking ? code does not check that case
 #ifdef CONFIG_IOTHREAD
    fcntl(d->pipe[0], F_SETFL, O_NONBLOCK);
 #else
    fcntl(d->pipe[0], F_SETFL, O_NONBLOCK /* | O_ASYNC */);
 #endif
    fcntl(d->pipe[1], F_SETFL, O_NONBLOCK);
-#endif //(if 0)
 
    fcntl(d->pipe[0], F_SETOWN, getpid());
 
diff --git a/ui/spice-display.h b/ui/spice-display.h
index e1fc398..37ce297 100644
--- a/ui/spice-display.h
+++ b/ui/spice-display.h
@@ -48,6 +48,7 @@ typedef struct SimpleSpiceDisplay {
 
     /* ssd updates (one request/command at a time) */
     struct SimpleSpiceUpdate *update;
+    int waiting_for_update;
 } SimpleSpiceDisplay;
 
 typedef struct SimpleSpiceUpdate {
-- 
1.7.4.1