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Re: [Qemu-devel] [v2][PATCH 2/2] libxl: introduce gfx_passthru_kind


From: Chen, Tiejun
Subject: Re: [Qemu-devel] [v2][PATCH 2/2] libxl: introduce gfx_passthru_kind
Date: Fri, 20 Mar 2015 09:04:07 +0800
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0



On 2015/3/19 18:44, Ian Campbell wrote:
On Thu, 2015-03-19 at 10:07 +0800, Chen, Tiejun wrote:
This duplicates the code from above. I think this would be best done as:

static int libxl__detect_gfx_passthru_kind(libxl__gc *gc, guest_config)
{
      if (b_info->u.hvm.gfx_passthru_kind != LIBXL_GFX_PASSTHRU_KIND_DEFAULT)
          return 0;

      if (libxl__is_igd_vga_passthru(gc, guest_config)) {
          b_info->u.hvm.gfx_passthru_kind = LIBXL_GFX_PASSTHRU_KIND_IGD;
          return 0;
      }

      LOG(ERROR, "Unable to detect graphics passthru kind");
      return 1;
}

Then for the code in libxl__build_device_model_args_new:

           if (libxl_defbool_val(b_info->u.hvm.gfx_passthru)) {
               if (!libxl__detect_gfx_passthru_kind(gc, guest_config))
                    return NULL
               switch (b_info->u.hvm.gfx_passthru_kind) {
               case LIBXL_GFX_PASSTHRU_KIND_IGD:
                   machinearg = GCSPRINTF("%s,igd-passthru=on", machinearg);
                   break;
               default:
                   LOG(ERROR, "unknown gfx_passthru_kind\n");
                  return NULL;
               }
          }

That is, a helper to try and autodetect kind if it is default and then a
single switch entry for each kind.

+            default:
+                LOG(WARN, "gfx_passthru_kind is invalid so ignored.\n");

Please return an error here, as I've shown above.

Looks good and thanks, but here 'guest_config' is a const so we
shouldn't/can't reset b_info->u.hvm.gfx_passthru_kind like this,

b_info->u.hvm.gfx_passthru_kind = LIBXL_GFX_PASSTHRU_KIND_IGD;

So I tried to refactor a little bit to follow up yours,

diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
index 8599a6a..605b17c 100644
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -409,6 +409,23 @@ static char *dm_spice_options(libxl__gc *gc,
       return opt;
   }

+static int
+libxl__detect_gfx_passthru_kind(libxl__gc *gc,
+                                const libxl_domain_config *guest_config)
+{
+    const libxl_domain_build_info *b_info = &guest_config->b_info;
+
+    if (b_info->u.hvm.gfx_passthru_kind != LIBXL_GFX_PASSTHRU_KIND_DEFAULT)
+        return b_info->u.hvm.gfx_passthru_kind;
+
+    if (libxl__is_igd_vga_passthru(gc, guest_config)) {
+        return LIBXL_GFX_PASSTHRU_KIND_IGD;
+    }
+
+    LOG(ERROR, "Unable to detect graphics passthru kind");
+    return -1;

I think you can make this function return enum
libxl_gfx_passthrough_kind and then return
LIBXL_GFX_PASSTHRU_KIND_DEFAULT in this case.

+}
+
   static char ** libxl__build_device_model_args_new(libxl__gc *gc,
                                           const char *dm, int guest_domid,
                                           const libxl_domain_config
*guest_config,
@@ -427,7 +444,7 @@ static char **
libxl__build_device_model_args_new(libxl__gc *gc,
       const char *keymap = dm_keymap(guest_config);
       char *machinearg;
       flexarray_t *dm_args;
-    int i, connection, devid;
+    int i, connection, devid, gfx_passthru_kind;

Please declare this in the smallest necessary scope...
[...]
+        if (libxl_defbool_val(b_info->u.hvm.gfx_passthru)) {
+            gfx_passthru_kind = libxl__detect_gfx_passthru_kind(gc,

i.e. here.

+
guest_config);
+            switch (gfx_passthru_kind) {
+            case LIBXL_GFX_PASSTHRU_KIND_IGD:
+                machinearg = GCSPRINTF("%s,igd-passthru=on", machinearg);
+                break;
+            default:

With the suggestion to return KIND_DEFAULT if detection fails then I
think an extra case should be added:
         case LIBXL_GFX_PASSTHRU_KIND_DEFAULT:
                 LOG(ERROR, "unable to detect required
                 gfx_passthru_kind");
                 return NULL;

+                LOG(ERROR, "unknown gfx_passthru_kind\n");

I think LOG is supposed to not include the final \n.


Refactor again,

diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
index 8599a6a..05c8916 100644
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -409,6 +409,23 @@ static char *dm_spice_options(libxl__gc *gc,
     return opt;
 }

+static enum libxl_gfx_passthru_kind
+libxl__detect_gfx_passthru_kind(libxl__gc *gc,
+                                const libxl_domain_config *guest_config)
+{
+    const libxl_domain_build_info *b_info = &guest_config->b_info;
+
+    if (b_info->u.hvm.gfx_passthru_kind != LIBXL_GFX_PASSTHRU_KIND_DEFAULT)
+        return b_info->u.hvm.gfx_passthru_kind;
+
+    if (libxl__is_igd_vga_passthru(gc, guest_config)) {
+        return LIBXL_GFX_PASSTHRU_KIND_IGD;
+    }
+
+    LOG(ERROR, "Unable to detect graphics passthru kind");
+    return LIBXL_GFX_PASSTHRU_KIND_DEFAULT;
+}
+
 static char ** libxl__build_device_model_args_new(libxl__gc *gc,
                                         const char *dm, int guest_domid,
const libxl_domain_config *guest_config, @@ -757,6 +771,21 @@ static char ** libxl__build_device_model_args_new(libxl__gc *gc,
                                             machinearg, max_ram_below_4g);
             }
         }
+
+        if (libxl_defbool_val(b_info->u.hvm.gfx_passthru)) {
+            enum libxl_gfx_passthru_kind gfx_passthru_kind =
+ libxl__detect_gfx_passthru_kind(gc, guest_config);
+            switch (gfx_passthru_kind) {
+            case LIBXL_GFX_PASSTHRU_KIND_IGD:
+                machinearg = GCSPRINTF("%s,igd-passthru=on", machinearg);
+                break;
+            case LIBXL_GFX_PASSTHRU_KIND_DEFAULT:
+                LOG(ERROR, "unable to detect required gfx_passthru_kind");
+            default:
+                return NULL;
+            }
+        }
+
         flexarray_append(dm_args, machinearg);
for (i = 0; b_info->extra_hvm && b_info->extra_hvm[i] != NULL; i++)
             flexarray_append(dm_args, b_info->extra_hvm[i]);


Thanks
Tiejun



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