Kernel: Make KString factories return KResultOr + use TRY() everywhere

There are a number of places that don't have an error propagation path
right now, so I've added FIXME's about that.

Kernel/FileSystem/Custody.cpp

@@ -33,15 +33,10 @@ KResultOr<NonnullRefPtr<Custody>> Custody::try_create(Custody* parent, StringVie
             }
         }
 
-        auto name_kstring = KString::try_create(name);
-        if (!name_kstring)
-            return ENOMEM;
-        auto custody = adopt_ref_if_nonnull(new (nothrow) Custody(parent, name_kstring.release_nonnull(), inode, mount_flags));
-        if (!custody)
-            return ENOMEM;
-
+        auto name_kstring = TRY(KString::try_create(name));
+        auto custody = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) Custody(parent, move(name_kstring), inode, mount_flags)));
         all_custodies.prepend(*custody);
-        return custody.release_nonnull();
+        return custody;
     });
 }
 
@@ -73,12 +68,8 @@ Custody::~Custody()
 
 KResultOr<NonnullOwnPtr<KString>> Custody::try_serialize_absolute_path() const
 {
-    if (!parent()) {
-        auto string = KString::try_create("/"sv);
-        if (!string)
-            return ENOMEM;
-        return string.release_nonnull();
-    }
+    if (!parent())
+        return KString::try_create("/"sv);
 
     Vector<Custody const*, 32> custody_chain;
     size_t path_length = 0;
@@ -89,9 +80,7 @@ KResultOr<NonnullOwnPtr<KString>> Custody::try_serialize_absolute_path() const
     VERIFY(path_length > 0);
 
     char* buffer;
-    auto string = KString::try_create_uninitialized(path_length - 1, buffer);
-    if (!string)
-        return ENOMEM;
+    auto string = TRY(KString::try_create_uninitialized(path_length - 1, buffer));
     size_t string_index = 0;
     for (size_t custody_index = custody_chain.size() - 1; custody_index > 0; --custody_index) {
         buffer[string_index] = '/';
@@ -102,7 +91,7 @@ KResultOr<NonnullOwnPtr<KString>> Custody::try_serialize_absolute_path() const
     }
     VERIFY(string->length() == string_index);
     buffer[string_index] = 0;
-    return string.release_nonnull();
+    return string;
 }
 
 String Custody::absolute_path() const

Kernel/FileSystem/DevFS.cpp

@@ -21,11 +21,10 @@ DevFS::DevFS()
 
 void DevFS::notify_new_device(Device& device)
 {
-    auto name = KString::try_create(device.device_name());
-    VERIFY(name);
-
+    // FIXME: Handle KString allocation failure.
+    auto name = KString::try_create(device.device_name()).release_value();
     MutexLocker locker(m_lock);
-    auto new_device_inode = adopt_ref(*new DevFSDeviceInode(*this, device, name.release_nonnull()));
+    auto new_device_inode = adopt_ref(*new DevFSDeviceInode(*this, device, move(name)));
     m_nodes.append(new_device_inode);
     m_root_inode->m_devices.append(new_device_inode);
 }
@@ -276,10 +275,8 @@ KResultOr<NonnullRefPtr<Inode>> DevFSRootDirectoryInode::create_child(StringView
             if (link.name() == name)
                 return EEXIST;
         }
-        auto name_kstring = KString::try_create(name);
-        if (!name_kstring)
-            return ENOMEM;
-        auto new_link_inode = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) DevFSLinkInode(fs(), name_kstring.release_nonnull())));
+        auto name_kstring = TRY(KString::try_create(name));
+        auto new_link_inode = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) DevFSLinkInode(fs(), move(name_kstring))));
         if (!m_links.try_ensure_capacity(m_links.size() + 1))
             return ENOMEM;
         if (!fs().m_nodes.try_ensure_capacity(fs().m_nodes.size() + 1))

Kernel/FileSystem/SysFSComponent.cpp

@@ -21,7 +21,7 @@ static size_t allocate_inode_index()
 }
 
 SysFSComponent::SysFSComponent(StringView name)
-    : m_name(KString::try_create(name).release_nonnull())
+    : m_name(KString::try_create(name).release_value()) // FIXME: Handle KString allocation failure.
     , m_component_index(allocate_inode_index())
 {
 }

Kernel/FileSystem/TmpFS.cpp

@@ -282,11 +282,8 @@ KResult TmpFSInode::add_child(Inode& child, StringView const& name, mode_t)
     if (name.length() > NAME_MAX)
         return ENAMETOOLONG;
 
-    auto name_kstring = KString::try_create(name);
-    if (!name_kstring)
-        return ENOMEM;
-
-    auto* child_entry = new (nothrow) Child { name_kstring.release_nonnull(), static_cast<TmpFSInode&>(child) };
+    auto name_kstring = TRY(KString::try_create(name));
+    auto* child_entry = new (nothrow) Child { move(name_kstring), static_cast<TmpFSInode&>(child) };
     if (!child_entry)
         return ENOMEM;
 

Kernel/FileSystem/VirtualFileSystem.cpp

@@ -323,9 +323,7 @@ KResultOr<NonnullRefPtr<FileDescription>> VirtualFileSystem::create(StringView p
 {
     auto basename = KLexicalPath::basename(path);
     auto parent_path = TRY(parent_custody.try_serialize_absolute_path());
-    auto full_path = KLexicalPath::try_join(parent_path->view(), basename);
-    if (!full_path)
-        return ENOMEM;
+    auto full_path = TRY(KLexicalPath::try_join(parent_path->view(), basename));
     TRY(validate_path_against_process_veil(full_path->view(), options));
 
     if (!is_socket(mode) && !is_fifo(mode) && !is_block_device(mode) && !is_character_device(mode)) {