AK+Kernel: Handle allocation failures in Device::try_make_request

This adds try_* methods to AK::DoublyLinkedList and updates the Device
class to use those to gracefully handle allocation failures.

Refs #6369.

AK/DoublyLinkedList.h

@@ -7,6 +7,7 @@
 #pragma once
 
 #include <AK/Assertions.h>
+#include <AK/Error.h>
 #include <AK/Find.h>
 #include <AK/StdLibExtras.h>
 
@@ -91,41 +92,61 @@ class DoublyLinkedList {
  }
 
  template<typename U>
- void append(U&& value)
+ ErrorOr<void> try_append(U&& value)
  {
  static_assert(
  requires { T(value); }, "Conversion operator is missing.");
- auto* node = new Node(forward<U>(value));
+ auto* node = new (nothrow) Node(forward<U>(value));
+ if (!node)
+ return Error::from_errno(ENOMEM);
  if (!m_head) {
  VERIFY(!m_tail);
  m_head = node;
  m_tail = node;
- return;
+ return {};
  }
  VERIFY(m_tail);
  VERIFY(!node->next);
  m_tail->next = node;
  node->prev = m_tail;
  m_tail = node;
+ return {};
  }
 
  template<typename U>
- void prepend(U&& value)
+ ErrorOr<void> try_prepend(U&& value)
  {
  static_assert(IsSame<T, U>);
- auto* node = new Node(forward<U>(value));
+ auto* node = new (nothrow) Node(forward<U>(value));
+ if (!node)
+ return Error::from_errno(ENOMEM);
  if (!m_head) {
  VERIFY(!m_tail);
  m_head = node;
  m_tail = node;
- return;
+ return {};
  }
  VERIFY(m_tail);
  VERIFY(!node->prev);
  m_head->prev = node;
  node->next = m_head;
  m_head = node;
+ return {};
+ }
+
+#ifndef KERNEL
+ template<typename U>
+ void append(U&& value)
+ {
+ MUST(try_append(forward<U>(value)));
+ }
+
+ template<typename U>
+ void prepend(U&& value)
+ {
+ MUST(try_prepend(forward<U>(value)));
  }
+#endif
 
  [[nodiscard]] bool contains_slow(const T& value) const
  {

Kernel/Devices/Device.h

@@ -58,7 +58,7 @@ class Device : public File {
  auto request = TRY(adopt_nonnull_lock_ref_or_enomem(new (nothrow) AsyncRequestType(*this, forward<Args>(args)...)));
  SpinlockLocker lock(m_requests_lock);
  bool was_empty = m_requests.is_empty();
- m_requests.append(request);
+ TRY(m_requests.try_append(request));
  if (was_empty)
  request->do_start(move(lock));
  return request;