[Qemu-devel] [RFC v4 9/9] qxl-render: call ppm_save on bh

[Alon Levy]

This changes the behavior of the monitor command. After the previous
patch, there is no longer an option of deadlock with virt-manager, but
ppm_save is called too early, before the update has completed. With this
patch it is called at the correct moment, but that means there is a race
between the monitor command completing and the screendump file being saved.

The only solution is to use an asynchronous monitor command. For a
previous round of this see:
 http://lists.gnu.org/archive/html/qemu-devel/2011-10/msg02810.html

Since that's contentious, I'm suggesting we do something that is almost
correct and doesn't hang, instead of correct and hangs. The screendump
user can inotify on the directory and the file if need be. For casual
monitor usage there is no difference.

Signed-off-by: Alon Levy <address@hidden>
---
 hw/qxl-render.c    |   60 ++++++++++++++++++++++++++++++++++++++++++++++++---
 hw/qxl.c           |   13 ++++++++--
 hw/qxl.h           |    2 +-
 ui/spice-display.h |    2 +
 4 files changed, 69 insertions(+), 8 deletions(-)

diff --git a/hw/qxl-render.c b/hw/qxl-render.c
index 23e6929..4b34c6f 100644
--- a/hw/qxl-render.c
+++ b/hw/qxl-render.c
@@ -78,6 +78,11 @@ void qxl_render_resize(PCIQXLDevice *qxl)
     }
 }
 
+typedef struct QXLPPMSaveBHData {
+    PCIQXLDevice *qxl;
+    QXLCookie *cookie;
+} QXLPPMSaveBHData;
+
 static void qxl_render_clear_update_redraw_unlocked(PCIQXLDevice *qxl)
 {
     qxl->render_update_redraw = 0;
@@ -86,6 +91,33 @@ static void 
qxl_render_clear_update_redraw_unlocked(PCIQXLDevice *qxl)
     qxl->num_dirty_rects = 0;
 }
 
+static void qxl_render_ppm_save_bh(void *opaque)
+{
+    QXLPPMSaveBHData *data = opaque;
+    PCIQXLDevice *qxl = data->qxl;
+    QXLCookie *cookie = data->cookie;
+    QEMUBH *bh = cookie->u.render.ppm_save_bh;
+    QXLRect area = {
+        .left = 0,
+        .right = qxl->guest_primary.surface.width,
+        .top = 0,
+        .bottom = qxl->guest_primary.surface.height
+    };
+
+    qemu_mutex_lock(&qxl->ssd.lock);
+    dprint(qxl, 1, "%s: %p (primary %p)\n", __func__,
+           qxl->ssd.ds->surface->data, qxl->guest_primary.data);
+    qxl_flip(qxl, &area);
+    qxl_render_clear_update_redraw_unlocked(qxl);
+    ppm_save(cookie->u.render.filename, qxl->ssd.ds->surface);
+    g_free(cookie->u.render.filename);
+    g_free(cookie);
+    --qxl->render_update_cookie_num;
+    g_free(data);
+    qemu_mutex_unlock(&qxl->ssd.lock);
+    qemu_bh_delete(bh);
+}
+
 static void qxl_displaysurface_resize(PCIQXLDevice *qxl)
 {
     VGACommonState *vga = &qxl->vga;
@@ -143,16 +175,17 @@ static void qxl_render_update_area_unlocked(PCIQXLDevice 
*qxl)
  * callbacks are called by spice_server thread, defering to bh called from the
  * io thread.
  */
-void qxl_render_update(PCIQXLDevice *qxl)
+void qxl_render_update(PCIQXLDevice *qxl, const char *filename)
 {
     int redraw = 0;
     QXLCookie *cookie;
+    QEMUBH *ppm_save_bh;
+    QXLPPMSaveBHData *ppm_save_bh_data;
 
     qemu_mutex_lock(&qxl->ssd.lock);
 
     if (qxl->guest_primary.resized) {
         qxl->guest_primary.resized = 0;
-
         qxl->guest_primary.data = memory_region_get_ram_ptr(&qxl->vga.vram);
         dprint(qxl, 1, "%s: %dx%d, stride %d, bpp %d, depth %d\n",
                __FUNCTION__,
@@ -165,6 +198,12 @@ void qxl_render_update(PCIQXLDevice *qxl)
     }
 
     if (!qxl->guest_primary.commands) {
+        if (filename) {
+            dprint(qxl, 1, "%s: screendump with no pending commands\n",
+                   __func__);
+            qxl_render_update_area_unlocked(qxl);
+            ppm_save(filename, qxl->ssd.ds->surface);
+        }
         qemu_mutex_unlock(&qxl->ssd.lock);
         return;
     }
@@ -177,6 +216,14 @@ void qxl_render_update(PCIQXLDevice *qxl)
     cookie->u.render.area.top    = 0;
     cookie->u.render.area.bottom = qxl->guest_primary.surface.height;
     qxl->render_update_redraw_area = cookie->u.render.area;
+    if (filename) {
+        ppm_save_bh_data = g_malloc0(sizeof(*ppm_save_bh_data));
+        ppm_save_bh_data->qxl = qxl;
+        ppm_save_bh_data->cookie = cookie;
+        ppm_save_bh = qemu_bh_new(qxl_render_ppm_save_bh, ppm_save_bh_data);
+        cookie->u.render.filename = g_strdup(filename);
+        cookie->u.render.ppm_save_bh = ppm_save_bh;
+    }
     qxl->render_update_cookie_num++;
     qemu_mutex_unlock(&qxl->ssd.lock);
     qxl_spice_update_area(qxl, 0, &cookie->u.render.area, NULL,
@@ -202,9 +249,14 @@ void qxl_render_update_area_bh(void *opaque)
 void qxl_render_update_area_done(PCIQXLDevice *qxl, QXLCookie *cookie)
 {
     qemu_mutex_lock(&qxl->ssd.lock);
-    qxl->render_update_cookie_num--;
+    if (cookie->u.render.filename) {
+        dprint(qxl, 1, "%s: scheduling ppm_save_bh\n", __func__);
+        qemu_bh_schedule(cookie->u.render.ppm_save_bh);
+    } else {
+        --qxl->render_update_cookie_num;
+        g_free(cookie);
+    }
     qemu_mutex_unlock(&qxl->ssd.lock);
-    g_free(cookie);
 }
 
 static QEMUCursor *qxl_cursor(PCIQXLDevice *qxl, QXLCursor *cursor)
diff --git a/hw/qxl.c b/hw/qxl.c
index b4f84f2..82f9ffa 100644
--- a/hw/qxl.c
+++ b/hw/qxl.c
@@ -1480,7 +1480,7 @@ static void qxl_hw_update(void *opaque)
         break;
     case QXL_MODE_COMPAT:
     case QXL_MODE_NATIVE:
-        qxl_render_update(qxl);
+        qxl_render_update(qxl, NULL);
         break;
     default:
         break;
@@ -1502,8 +1502,15 @@ static void qxl_hw_screen_dump(void *opaque, const char 
*filename)
     switch (qxl->mode) {
     case QXL_MODE_COMPAT:
     case QXL_MODE_NATIVE:
-        qxl_render_update(qxl);
-        ppm_save(filename, qxl->ssd.ds->surface);
+        /*
+         * TODO: if we use an async update_area, to avoid deadlock with
+         * virt-manager, we postpone the saving of the image until the
+         * rendering is done. This means the image isn't guranteed to be
+         * written when we return to the monitor. Fixing this needs an async
+         * monitor command, whatever the implementation of the concept is
+         * called.
+         */
+        qxl_render_update(qxl, filename);
         break;
     case QXL_MODE_VGA:
         /*
diff --git a/hw/qxl.h b/hw/qxl.h
index 57a94ca..91297bd 100644
--- a/hw/qxl.h
+++ b/hw/qxl.h
@@ -138,7 +138,7 @@ void qxl_log_command(PCIQXLDevice *qxl, const char *ring, 
QXLCommandExt *ext);
 
 /* qxl-render.c */
 void qxl_render_resize(PCIQXLDevice *qxl);
-void qxl_render_update(PCIQXLDevice *qxl);
+void qxl_render_update(PCIQXLDevice *qxl, const char *filename);
 void qxl_render_cursor(PCIQXLDevice *qxl, QXLCommandExt *ext);
 void qxl_render_update_area_done(PCIQXLDevice *qxl, QXLCookie *cookie);
 void qxl_render_update_area_bh(void *opaque);
diff --git a/ui/spice-display.h b/ui/spice-display.h
index 81fa1e4..076e0e5 100644
--- a/ui/spice-display.h
+++ b/ui/spice-display.h
@@ -62,6 +62,8 @@ typedef struct QXLCookie {
         struct {
             QXLRect area;
             int redraw;
+            char *filename;
+            QEMUBH *ppm_save_bh;
         } render;
     } u;
 } QXLCookie;
-- 
1.7.9.1