CDImage: Add Precache() method

src/common/cd_image.cpp

@@ -324,6 +324,11 @@ std::string CDImage::GetSubImageMetadata(u32 index, const std::string_view& type
   return {};
 }
 
+CDImage::PrecacheResult CDImage::Precache(ProgressCallback* progress /*= ProgressCallback::NullProgressCallback*/)
+{
+  return PrecacheResult::Unsupported;
+}
+
 void CDImage::ClearTOC()
 {
   m_lba_count = 0;

src/common/cd_image.h

@@ -57,6 +57,13 @@ public:
     Mode2Raw      // 2352 bytes per sector
   };
 
+  enum class PrecacheResult : u8
+  {
+    Unsupported,
+    ReadError,
+    Success,
+  };
+
   struct SectorHeader
   {
     u8 minute;
@@ -294,6 +301,9 @@ public:
   // Retrieve sub-image metadata.
   virtual std::string GetSubImageMetadata(u32 index, const std::string_view& type) const;
 
+  // Returns true if the source supports precaching, which may be more optimal than an in-memory copy.
+  virtual PrecacheResult Precache(ProgressCallback* progress = ProgressCallback::NullProgressCallback);
+
 protected:
   void ClearTOC();
   void CopyTOC(const CDImage* image);

src/core/system.cpp

@@ -683,11 +683,22 @@ std::unique_ptr<CDImage> OpenCDImage(const char* path, Common::Error* error, boo
     else
     {
       HostInterfaceProgressCallback callback;
-      std::unique_ptr<CDImage> memory_image = CDImage::CreateMemoryImage(media.get(), &callback);
-      if (memory_image)
-        media = std::move(memory_image);
-      else
-        Log_WarningPrintf("Failed to preload image '%s' to RAM", path);
+      const CDImage::PrecacheResult res = media->Precache(&callback);
+      if (res == CDImage::PrecacheResult::Unsupported)
+      {
+        // fall back to copy precaching
+        std::unique_ptr<CDImage> memory_image = CDImage::CreateMemoryImage(media.get(), &callback);
+        if (memory_image)
+          media = std::move(memory_image);
+        else
+          Log_WarningPrintf("Failed to preload image '%s' to RAM", path);
+      }
+      else if (res != CDImage::PrecacheResult::Success)
+      {
+        g_host_interface->AddOSDMessage(
+          g_host_interface->TranslateStdString("OSDMessage", "Precaching CD image failed, it may be unreliable."),
+          15.0f);
+      }
     }
   }