hw/display: factor out the scanout blob to fb conversion

There are two identical sequences of a code doing the same thing that
raise warnings with Coverity. Before fixing those issues lets factor
out the common code into a helper function we can share.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Message-ID: <20241111230040.68470-2-alex.bennee@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

hw/display/virtio-gpu-virgl.c

@@ -805,7 +805,6 @@ static void virgl_cmd_set_scanout_blob(VirtIOGPU *g,
     struct virtio_gpu_framebuffer fb = { 0 };
     struct virtio_gpu_virgl_resource *res;
     struct virtio_gpu_set_scanout_blob ss;
-    uint64_t fbend;
 
     VIRTIO_GPU_FILL_CMD(ss);
     virtio_gpu_scanout_blob_bswap(&ss);
@@ -852,26 +851,7 @@ static void virgl_cmd_set_scanout_blob(VirtIOGPU *g,
         return;
     }
 
-    fb.format = virtio_gpu_get_pixman_format(ss.format);
-    if (!fb.format) {
-        qemu_log_mask(LOG_GUEST_ERROR, "%s: pixel format not supported %d\n",
-                      __func__, ss.format);
-        cmd->error = VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER;
-        return;
-    }
-
-    fb.bytes_pp = DIV_ROUND_UP(PIXMAN_FORMAT_BPP(fb.format), 8);
-    fb.width = ss.width;
-    fb.height = ss.height;
-    fb.stride = ss.strides[0];
-    fb.offset = ss.offsets[0] + ss.r.x * fb.bytes_pp + ss.r.y * fb.stride;
-
-    fbend = fb.offset;
-    fbend += fb.stride * (ss.r.height - 1);
-    fbend += fb.bytes_pp * ss.r.width;
-    if (fbend > res->base.blob_size) {
-        qemu_log_mask(LOG_GUEST_ERROR, "%s: fb end out of range\n",
-                      __func__);
+    if (!virtio_gpu_scanout_blob_to_fb(&fb, &ss, res->base.blob_size)) {
         cmd->error = VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER;
         return;
     }

hw/display/virtio-gpu.c

@@ -721,13 +721,48 @@ static void virtio_gpu_set_scanout(VirtIOGPU *g,
                               &fb, res, &ss.r, &cmd->error);
 }
 
+bool virtio_gpu_scanout_blob_to_fb(struct virtio_gpu_framebuffer *fb,
+                                   struct virtio_gpu_set_scanout_blob *ss,
+                                   uint64_t blob_size)
+{
+    uint64_t fbend;
+
+    fb->format = virtio_gpu_get_pixman_format(ss->format);
+    if (!fb->format) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: host couldn't handle guest format %d\n",
+                      __func__, ss->format);
+        return false;
+    }
+
+    fb->bytes_pp = DIV_ROUND_UP(PIXMAN_FORMAT_BPP(fb->format), 8);
+    fb->width = ss->width;
+    fb->height = ss->height;
+    fb->stride = ss->strides[0];
+    fb->offset = ss->offsets[0] + ss->r.x * fb->bytes_pp + ss->r.y * fb->stride;
+
+    fbend = fb->offset;
+    fbend += fb->stride * (ss->r.height - 1);
+    fbend += fb->bytes_pp * ss->r.width;
+
+    if (fbend > blob_size) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: fb end out of range\n",
+                      __func__);
+        return false;
+    }
+
+    return true;
+}
+
+
+
 static void virtio_gpu_set_scanout_blob(VirtIOGPU *g,
                                         struct virtio_gpu_ctrl_command *cmd)
 {
     struct virtio_gpu_simple_resource *res;
     struct virtio_gpu_framebuffer fb = { 0 };
     struct virtio_gpu_set_scanout_blob ss;
-    uint64_t fbend;
 
     VIRTIO_GPU_FILL_CMD(ss);
     virtio_gpu_scanout_blob_bswap(&ss);
@@ -753,28 +788,7 @@ static void virtio_gpu_set_scanout_blob(VirtIOGPU *g,
         return;
     }
 
-    fb.format = virtio_gpu_get_pixman_format(ss.format);
-    if (!fb.format) {
-        qemu_log_mask(LOG_GUEST_ERROR,
-                      "%s: host couldn't handle guest format %d\n",
-                      __func__, ss.format);
-        cmd->error = VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER;
-        return;
-    }
-
-    fb.bytes_pp = DIV_ROUND_UP(PIXMAN_FORMAT_BPP(fb.format), 8);
-    fb.width = ss.width;
-    fb.height = ss.height;
-    fb.stride = ss.strides[0];
-    fb.offset = ss.offsets[0] + ss.r.x * fb.bytes_pp + ss.r.y * fb.stride;
-
-    fbend = fb.offset;
-    fbend += fb.stride * (ss.r.height - 1);
-    fbend += fb.bytes_pp * ss.r.width;
-    if (fbend > res->blob_size) {
-        qemu_log_mask(LOG_GUEST_ERROR,
-                      "%s: fb end out of range\n",
-                      __func__);
+    if (!virtio_gpu_scanout_blob_to_fb(&fb, &ss, res->blob_size)) {
         cmd->error = VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER;
         return;
     }

include/hw/virtio/virtio-gpu.h

@@ -333,6 +333,21 @@ void virtio_gpu_update_cursor_data(VirtIOGPU *g,
                                    struct virtio_gpu_scanout *s,
                                    uint32_t resource_id);
 
+/**
+ * virtio_gpu_scanout_blob_to_fb() - fill out fb based on scanout data
+ * fb: the frame-buffer descriptor to fill out
+ * ss: the scanout blob data
+ * blob_size: size of scanout blob data
+ *
+ * This will check we have enough space for the frame taking into
+ * account that stride for all but the last line.
+ *
+ * Returns true on success, otherwise logs guest error and returns false
+ */
+bool virtio_gpu_scanout_blob_to_fb(struct virtio_gpu_framebuffer *fb,
+                                   struct virtio_gpu_set_scanout_blob *ss,
+                                   uint64_t blob_size);
+
 /* virtio-gpu-udmabuf.c */
 bool virtio_gpu_have_udmabuf(void);
 void virtio_gpu_init_udmabuf(struct virtio_gpu_simple_resource *res);