Kernel/ScatterGatherList: Return ErrorOr from try_create

This removes the TODO from the try_create API to return ErrorOr. This
is also a preparation patch to move the init code in the constructor
that can fail to this try_create function.

Kernel/Memory/ScatterGatherList.cpp

@@ -8,14 +8,10 @@
 
 namespace Kernel::Memory {
 
-LockRefPtr<ScatterGatherList> ScatterGatherList::try_create(AsyncBlockDeviceRequest& request, Span<NonnullRefPtr<PhysicalPage>> allocated_pages, size_t device_block_size)
+ErrorOr<LockRefPtr<ScatterGatherList>> ScatterGatherList::try_create(AsyncBlockDeviceRequest& request, Span<NonnullRefPtr<PhysicalPage>> allocated_pages, size_t device_block_size)
 {
-    auto maybe_vm_object = AnonymousVMObject::try_create_with_physical_pages(allocated_pages);
-    if (maybe_vm_object.is_error()) {
-        // FIXME: Would be nice to be able to return a ErrorOr here.
-        return {};
-    }
-    return adopt_lock_ref_if_nonnull(new (nothrow) ScatterGatherList(maybe_vm_object.release_value(), request, device_block_size));
+    auto vm_object = TRY(AnonymousVMObject::try_create_with_physical_pages(allocated_pages));
+    return adopt_lock_ref_if_nonnull(new (nothrow) ScatterGatherList(vm_object, request, device_block_size));
 }
 
 ScatterGatherList::ScatterGatherList(NonnullLockRefPtr<AnonymousVMObject> vm_object, AsyncBlockDeviceRequest& request, size_t device_block_size)

Kernel/Memory/ScatterGatherList.h

@@ -19,7 +19,7 @@ namespace Kernel::Memory {
 
 class ScatterGatherList final : public AtomicRefCounted<ScatterGatherList> {
 public:
-    static LockRefPtr<ScatterGatherList> try_create(AsyncBlockDeviceRequest&, Span<NonnullRefPtr<PhysicalPage>> allocated_pages, size_t device_block_size);
+    static ErrorOr<LockRefPtr<ScatterGatherList>> try_create(AsyncBlockDeviceRequest&, Span<NonnullRefPtr<PhysicalPage>> allocated_pages, size_t device_block_size);
     VMObject const& vmobject() const { return m_vm_object; }
     VirtualAddress dma_region() const { return m_dma_region->vaddr(); }
     size_t scatters_count() const { return m_vm_object->physical_pages().size(); }

Kernel/Storage/ATA/AHCI/Port.cpp

@@ -429,7 +429,7 @@ Optional<AsyncDeviceRequest::RequestResult> AHCIPort::prepare_and_set_scatter_li
         allocated_dma_regions.append(m_dma_buffers.at(index));
     }
 
-    m_current_scatter_list = Memory::ScatterGatherList::try_create(request, allocated_dma_regions.span(), m_connected_device->block_size());
+    m_current_scatter_list = Memory::ScatterGatherList::try_create(request, allocated_dma_regions.span(), m_connected_device->block_size()).release_value_but_fixme_should_propagate_errors();
     if (!m_current_scatter_list)
         return AsyncDeviceRequest::Failure;
     if (request.request_type() == AsyncBlockDeviceRequest::Write) {