Kernel: Allocate VirtIOGPU context IDs from a bitmap, with ErrorOr

As is, we never *deallocate* them, so we will run out eventually.

Creating a context, or allocating a context ID, now returns ErrorOr if
there are no available free context IDs.

`number_of_fixmes--;` :^)

3 files changed, 32 insertions, 13 deletions

diff --git a/Kernel/Graphics/VirtIOGPU/GPU3DDevice.cpp b/Kernel/Graphics/VirtIOGPU/GPU3DDevice.cpp
index 90f0fcc4dc..3ed02a12d1 100644
--- a/Kernel/Graphics/VirtIOGPU/GPU3DDevice.cpp
+++ b/Kernel/Graphics/VirtIOGPU/GPU3DDevice.cpp
@@ -39,7 +39,7 @@ VirtIOGPU3DDevice::VirtIOGPU3DDevice(VirtIOGraphicsAdapter const& graphics_adapt
     , m_graphics_adapter(graphics_adapter)
     , m_transfer_buffer_region(move(transfer_buffer_region))
 {
-    m_kernel_context_id = m_graphics_adapter->create_context();
+    m_kernel_context_id = MUST(m_graphics_adapter->create_context());
 }
 
 void VirtIOGPU3DDevice::detach(OpenFileDescription& description)
@@ -65,7 +65,7 @@ ErrorOr<void> VirtIOGPU3DDevice::ioctl(OpenFileDescription& description, unsigne
             return EEXIST;
         SpinlockLocker locker(m_graphics_adapter->operation_lock());
         // TODO: Delete the context if it fails to be set in m_context_state_lookup
-        auto context_id = m_graphics_adapter->create_context();
+        auto context_id = TRY(m_graphics_adapter->create_context());
         LockRefPtr<PerContextState> per_context_state = TRY(PerContextState::try_create(context_id));
         TRY(m_context_state_lookup.try_set(&description, per_context_state));
         return {};
diff --git a/Kernel/Graphics/VirtIOGPU/GraphicsAdapter.cpp b/Kernel/Graphics/VirtIOGPU/GraphicsAdapter.cpp
index 1c0a37bbed..be3059316d 100644
--- a/Kernel/Graphics/VirtIOGPU/GraphicsAdapter.cpp
+++ b/Kernel/Graphics/VirtIOGPU/GraphicsAdapter.cpp
@@ -30,7 +30,8 @@ NonnullLockRefPtr<VirtIOGraphicsAdapter> VirtIOGraphicsAdapter::initialize(PCI::
         "VirtGPU Scratch Space"sv,
         Memory::Region::Access::ReadWrite));
 
-    auto adapter = adopt_lock_ref(*new (nothrow) VirtIOGraphicsAdapter(device_identifier, move(scratch_space_region)));
+    auto active_context_ids = Bitmap::must_create(VREND_MAX_CTX, false);
+    auto adapter = adopt_lock_ref(*new (nothrow) VirtIOGraphicsAdapter(device_identifier, move(active_context_ids), move(scratch_space_region)));
     adapter->initialize();
     MUST(adapter->initialize_adapter());
     return adapter;
@@ -125,10 +126,15 @@ ErrorOr<void> VirtIOGraphicsAdapter::attach_physical_range_to_framebuffer(VirtIO
     return {};
 }
 
-VirtIOGraphicsAdapter::VirtIOGraphicsAdapter(PCI::DeviceIdentifier const& device_identifier, NonnullOwnPtr<Memory::Region> scratch_space_region)
+VirtIOGraphicsAdapter::VirtIOGraphicsAdapter(PCI::DeviceIdentifier const& device_identifier, Bitmap&& active_context_ids, NonnullOwnPtr<Memory::Region> scratch_space_region)
     : VirtIO::Device(device_identifier)
     , m_scratch_space(move(scratch_space_region))
 {
+    m_active_context_ids.with([&](Bitmap& my_active_context_ids) {
+        my_active_context_ids = move(active_context_ids);
+        // Note: Context ID 0 is invalid, so mark it as in use.
+        my_active_context_ids.set(0, true);
+    });
 }
 
 void VirtIOGraphicsAdapter::initialize()
@@ -410,10 +416,23 @@ Graphics::VirtIOGPU::ResourceID VirtIOGraphicsAdapter::allocate_resource_id()
     return m_resource_id_counter++;
 }
 
-Graphics::VirtIOGPU::ContextID VirtIOGraphicsAdapter::allocate_context_id()
+ErrorOr<Graphics::VirtIOGPU::ContextID> VirtIOGraphicsAdapter::allocate_context_id()
 {
-    // FIXME: This should really be tracked using a bitmap, instead of an atomic counter
-    return m_context_id_counter++;
+    Optional<Graphics::VirtIOGPU::ContextID> new_context_id;
+
+    m_active_context_ids.with([&new_context_id](Bitmap& active_context_ids) {
+        auto maybe_available_id = active_context_ids.find_first_unset();
+        if (!maybe_available_id.has_value())
+            return;
+        new_context_id = maybe_available_id.value();
+        active_context_ids.set(maybe_available_id.value(), true);
+    });
+
+    if (new_context_id.has_value())
+        return new_context_id.value();
+
+    dmesgln("VirtIO::GraphicsAdapter: No available context IDs.");
+    return Error::from_errno(ENXIO);
 }
 
 void VirtIOGraphicsAdapter::delete_resource(Graphics::VirtIOGPU::ResourceID resource_id)
@@ -439,10 +458,10 @@ void VirtIOGraphicsAdapter::initialize_3d_device()
     }
 }
 
-Graphics::VirtIOGPU::ContextID VirtIOGraphicsAdapter::create_context()
+ErrorOr<Graphics::VirtIOGPU::ContextID> VirtIOGraphicsAdapter::create_context()
 {
     VERIFY(m_operation_lock.is_locked());
-    auto ctx_id = allocate_context_id();
+    auto ctx_id = TRY(allocate_context_id());
     auto writer = create_scratchspace_writer();
     auto& request = writer.append_structure<Graphics::VirtIOGPU::Protocol::ContextCreate>();
     auto& response = writer.append_structure<Graphics::VirtIOGPU::Protocol::ControlHeader>();
diff --git a/Kernel/Graphics/VirtIOGPU/GraphicsAdapter.h b/Kernel/Graphics/VirtIOGPU/GraphicsAdapter.h
index 0e35d162b8..81e496a202 100644
--- a/Kernel/Graphics/VirtIOGPU/GraphicsAdapter.h
+++ b/Kernel/Graphics/VirtIOGPU/GraphicsAdapter.h
@@ -63,7 +63,7 @@ private:
         PhysicalBuffer back_buffer;
     };
 
-    VirtIOGraphicsAdapter(PCI::DeviceIdentifier const&, NonnullOwnPtr<Memory::Region> scratch_space_region);
+    VirtIOGraphicsAdapter(PCI::DeviceIdentifier const&, Bitmap&& active_context_ids, NonnullOwnPtr<Memory::Region> scratch_space_region);
 
     ErrorOr<void> initialize_adapter();
 
@@ -80,14 +80,14 @@ private:
     }
 
     // 3D Command stuff
-    Graphics::VirtIOGPU::ContextID create_context();
+    ErrorOr<Graphics::VirtIOGPU::ContextID> create_context();
     void attach_resource_to_context(Graphics::VirtIOGPU::ResourceID resource_id, Graphics::VirtIOGPU::ContextID context_id);
     void submit_command_buffer(Graphics::VirtIOGPU::ContextID, Function<size_t(Bytes)> buffer_writer);
     Graphics::VirtIOGPU::Protocol::TextureFormat get_framebuffer_format() const { return Graphics::VirtIOGPU::Protocol::TextureFormat::VIRTIO_GPU_FORMAT_B8G8R8X8_UNORM; }
 
     auto& operation_lock() { return m_operation_lock; }
     Graphics::VirtIOGPU::ResourceID allocate_resource_id();
-    Graphics::VirtIOGPU::ContextID allocate_context_id();
+    ErrorOr<Graphics::VirtIOGPU::ContextID> allocate_context_id();
 
     PhysicalAddress start_of_scratch_space() const { return m_scratch_space->physical_page(0)->paddr(); }
     AK::BinaryBufferWriter create_scratchspace_writer()
@@ -113,7 +113,7 @@ private:
     VirtIO::Configuration const* m_device_configuration { nullptr };
     // Note: Resource ID 0 is invalid, and we must not allocate 0 as the first resource ID.
     Atomic<u32> m_resource_id_counter { 1 };
-    Atomic<u32> m_context_id_counter { 1 };
+    SpinlockProtected<Bitmap> m_active_context_ids { LockRank::None };
     LockRefPtr<VirtIOGPU3DDevice> m_3d_device;
     bool m_has_virgl_support { false };