Kernel: Make Inode::lookup() return a KResultOr<NonnullRefPtr<Inode>>

This allows file systems to return arbitrary error codes instead of just
an Inode or not an Inode.

18 files changed, 83 insertions, 72 deletions

diff --git a/Kernel/FileSystem/DevFS.cpp b/Kernel/FileSystem/DevFS.cpp
index 23332fa695..ed4c595900 100644
--- a/Kernel/FileSystem/DevFS.cpp
+++ b/Kernel/FileSystem/DevFS.cpp
@@ -93,7 +93,7 @@ KResult DevFSInode::traverse_as_directory(Function<bool(FileSystem::DirectoryEnt
     VERIFY_NOT_REACHED();
 }
 
-RefPtr<Inode> DevFSInode::lookup(StringView)
+KResultOr<NonnullRefPtr<Inode>> DevFSInode::lookup(StringView)
 {
     VERIFY_NOT_REACHED();
 }
@@ -206,15 +206,6 @@ InodeMetadata DevFSDirectoryInode::metadata() const
     metadata.mtime = mepoch;
     return metadata;
 }
-KResult DevFSDirectoryInode::traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const
-{
-    return EINVAL;
-}
-
-RefPtr<Inode> DevFSDirectoryInode::lookup(StringView)
-{
-    return nullptr;
-}
 
 DevFSRootDirectoryInode::DevFSRootDirectoryInode(DevFS& fs)
     : DevFSDirectoryInode(fs)
@@ -242,7 +233,8 @@ KResult DevFSRootDirectoryInode::traverse_as_directory(Function<bool(FileSystem:
     }
     return KSuccess;
 }
-RefPtr<Inode> DevFSRootDirectoryInode::lookup(StringView name)
+
+KResultOr<NonnullRefPtr<Inode>> DevFSRootDirectoryInode::lookup(StringView name)
 {
     MutexLocker locker(fs().m_lock);
     for (auto& subdirectory : m_subdirectories) {
@@ -259,7 +251,7 @@ RefPtr<Inode> DevFSRootDirectoryInode::lookup(StringView name)
             return device_node;
         }
     }
-    return nullptr;
+    return ENOENT;
 }
 KResultOr<NonnullRefPtr<Inode>> DevFSRootDirectoryInode::create_child(StringView name, mode_t mode, dev_t, uid_t, gid_t)
 {
@@ -395,10 +387,12 @@ KResult DevFSPtsDirectoryInode::traverse_as_directory(Function<bool(FileSystem::
     callback({ "..", identifier(), 0 });
     return KSuccess;
 }
-RefPtr<Inode> DevFSPtsDirectoryInode::lookup(StringView)
+
+KResultOr<NonnullRefPtr<Inode>> DevFSPtsDirectoryInode::lookup(StringView)
 {
-    return nullptr;
+    return ENOENT;
 }
+
 DevFSPtsDirectoryInode::~DevFSPtsDirectoryInode()
 {
 }
diff --git a/Kernel/FileSystem/DevFS.h b/Kernel/FileSystem/DevFS.h
index 557804e671..0f81af6394 100644
--- a/Kernel/FileSystem/DevFS.h
+++ b/Kernel/FileSystem/DevFS.h
@@ -55,7 +55,7 @@ protected:
     DevFSInode(DevFS&);
     virtual KResultOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer& buffer, FileDescription*) const override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual RefPtr<Inode> lookup(StringView name) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override;
     virtual void flush_metadata() override;
     virtual KResultOr<size_t> write_bytes(off_t, size_t, const UserOrKernelBuffer& buffer, FileDescription*) override;
     virtual KResultOr<NonnullRefPtr<Inode>> create_child(StringView name, mode_t, dev_t, uid_t, gid_t) override;
@@ -119,8 +119,6 @@ protected:
     DevFSDirectoryInode(DevFS&);
     // ^Inode
     virtual InodeMetadata metadata() const override;
-    virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual RefPtr<Inode> lookup(StringView name) override;
 
     NonnullRefPtrVector<DevFSDeviceInode> m_devices;
 };
@@ -136,7 +134,7 @@ public:
 private:
     explicit DevFSPtsDirectoryInode(DevFS&);
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual RefPtr<Inode> lookup(StringView name) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override;
     virtual InodeMetadata metadata() const override;
 };
 
@@ -151,7 +149,7 @@ private:
     explicit DevFSRootDirectoryInode(DevFS&);
     virtual KResultOr<NonnullRefPtr<Inode>> create_child(StringView name, mode_t, dev_t, uid_t, gid_t) override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual RefPtr<Inode> lookup(StringView name) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override;
     virtual InodeMetadata metadata() const override;
 
     NonnullRefPtrVector<DevFSDirectoryInode> m_subdirectories;
diff --git a/Kernel/FileSystem/DevPtsFS.cpp b/Kernel/FileSystem/DevPtsFS.cpp
index 80fc243211..ee5c2a4b46 100644
--- a/Kernel/FileSystem/DevPtsFS.cpp
+++ b/Kernel/FileSystem/DevPtsFS.cpp
@@ -136,21 +136,24 @@ KResult DevPtsFSInode::traverse_as_directory(Function<bool(FileSystem::Directory
     return KSuccess;
 }
 
-RefPtr<Inode> DevPtsFSInode::lookup(StringView name)
+KResultOr<NonnullRefPtr<Inode>> DevPtsFSInode::lookup(StringView name)
 {
     VERIFY(identifier().index() == 1);
 
     if (name == "." || name == "..")
-        return this;
+        return *this;
 
     auto& fs = static_cast<DevPtsFS&>(this->fs());
 
     auto pty_index = name.to_uint();
     if (pty_index.has_value() && s_ptys->contains(pty_index.value())) {
-        return fs.get_inode({ fsid(), pty_index_to_inode_index(pty_index.value()) });
+        auto inode = fs.get_inode({ fsid(), pty_index_to_inode_index(pty_index.value()) });
+        if (!inode)
+            return ENOENT;
+        return inode.release_nonnull();
     }
 
-    return {};
+    return ENOENT;
 }
 
 void DevPtsFSInode::flush_metadata()
diff --git a/Kernel/FileSystem/DevPtsFS.h b/Kernel/FileSystem/DevPtsFS.h
index 1fe8bad9a7..68c539bb42 100644
--- a/Kernel/FileSystem/DevPtsFS.h
+++ b/Kernel/FileSystem/DevPtsFS.h
@@ -50,7 +50,7 @@ private:
     virtual KResultOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer& buffer, FileDescription*) const override;
     virtual InodeMetadata metadata() const override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual RefPtr<Inode> lookup(StringView name) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override;
     virtual void flush_metadata() override;
     virtual KResultOr<size_t> write_bytes(off_t, size_t, const UserOrKernelBuffer& buffer, FileDescription*) override;
     virtual KResultOr<NonnullRefPtr<Inode>> create_child(StringView name, mode_t, dev_t, uid_t, gid_t) override;
diff --git a/Kernel/FileSystem/Ext2FileSystem.cpp b/Kernel/FileSystem/Ext2FileSystem.cpp
index 20876dc21d..b34582c934 100644
--- a/Kernel/FileSystem/Ext2FileSystem.cpp
+++ b/Kernel/FileSystem/Ext2FileSystem.cpp
@@ -1630,12 +1630,12 @@ KResult Ext2FSInode::populate_lookup_cache() const
     return KSuccess;
 }
 
-RefPtr<Inode> Ext2FSInode::lookup(StringView name)
+KResultOr<NonnullRefPtr<Inode>> Ext2FSInode::lookup(StringView name)
 {
     VERIFY(is_directory());
     dbgln_if(EXT2_DEBUG, "Ext2FSInode[{}]:lookup(): Looking up '{}'", identifier(), name);
-    if (populate_lookup_cache().is_error())
-        return {};
+    if (auto result = populate_lookup_cache(); result.is_error())
+        return result;
 
     InodeIndex inode_index;
     {
@@ -1643,11 +1643,15 @@ RefPtr<Inode> Ext2FSInode::lookup(StringView name)
         auto it = m_lookup_cache.find(name.hash(), [&](auto& entry) { return entry.key == name; });
         if (it == m_lookup_cache.end()) {
             dbgln_if(EXT2_DEBUG, "Ext2FSInode[{}]:lookup(): '{}' not found", identifier(), name);
-            return {};
+            return ENOENT;
         }
         inode_index = it->value;
     }
-    return fs().get_inode({ fsid(), inode_index });
+
+    auto inode = fs().get_inode({ fsid(), inode_index });
+    if (!inode)
+        return ENOENT;
+    return inode.release_nonnull();
 }
 
 void Ext2FSInode::one_ref_left()
diff --git a/Kernel/FileSystem/Ext2FileSystem.h b/Kernel/FileSystem/Ext2FileSystem.h
index d3f1161087..b434f63a15 100644
--- a/Kernel/FileSystem/Ext2FileSystem.h
+++ b/Kernel/FileSystem/Ext2FileSystem.h
@@ -41,7 +41,7 @@ private:
     virtual KResultOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer& buffer, FileDescription*) const override;
     virtual InodeMetadata metadata() const override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual RefPtr<Inode> lookup(StringView name) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override;
     virtual void flush_metadata() override;
     virtual KResultOr<size_t> write_bytes(off_t, size_t, const UserOrKernelBuffer& data, FileDescription*) override;
     virtual KResultOr<NonnullRefPtr<Inode>> create_child(StringView name, mode_t, dev_t, uid_t, gid_t) override;
diff --git a/Kernel/FileSystem/ISO9660FileSystem.cpp b/Kernel/FileSystem/ISO9660FileSystem.cpp
index 41e1e47600..3d2b852f0c 100644
--- a/Kernel/FileSystem/ISO9660FileSystem.cpp
+++ b/Kernel/FileSystem/ISO9660FileSystem.cpp
@@ -532,7 +532,7 @@ KResult ISO9660Inode::traverse_as_directory(Function<bool(FileSystem::DirectoryE
     return KSuccess;
 }
 
-RefPtr<Inode> ISO9660Inode::lookup(StringView name)
+KResultOr<NonnullRefPtr<Inode>> ISO9660Inode::lookup(StringView name)
 {
     auto& file_system = static_cast<ISO9660FS const&>(fs());
     RefPtr<Inode> inode;
@@ -558,11 +558,12 @@ RefPtr<Inode> ISO9660Inode::lookup(StringView name)
         return RecursionDecision::Continue;
     });
 
-    if (traversal_result.is_error()) {
-        return {};
-    }
+    if (traversal_result.is_error())
+        return traversal_result;
 
-    return inode;
+    if (!inode)
+        return ENOENT;
+    return inode.release_nonnull();
 }
 
 void ISO9660Inode::flush_metadata()
diff --git a/Kernel/FileSystem/ISO9660FileSystem.h b/Kernel/FileSystem/ISO9660FileSystem.h
index 65a160cd44..e4a46d3f32 100644
--- a/Kernel/FileSystem/ISO9660FileSystem.h
+++ b/Kernel/FileSystem/ISO9660FileSystem.h
@@ -351,7 +351,7 @@ public:
     virtual KResultOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer& buffer, FileDescription*) const override;
     virtual InodeMetadata metadata() const override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual RefPtr<Inode> lookup(StringView name) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override;
     virtual void flush_metadata() override;
     virtual KResultOr<size_t> write_bytes(off_t, size_t, const UserOrKernelBuffer& buffer, FileDescription*) override;
     virtual KResultOr<NonnullRefPtr<Inode>> create_child(StringView name, mode_t, dev_t, uid_t, gid_t) override;
diff --git a/Kernel/FileSystem/Inode.h b/Kernel/FileSystem/Inode.h
index c4c49909bd..cf77df7507 100644
--- a/Kernel/FileSystem/Inode.h
+++ b/Kernel/FileSystem/Inode.h
@@ -53,7 +53,7 @@ public:
     virtual void did_seek(FileDescription&, off_t) { }
     virtual KResultOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer& buffer, FileDescription*) const = 0;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const = 0;
-    virtual RefPtr<Inode> lookup(StringView name) = 0;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) = 0;
     virtual KResultOr<size_t> write_bytes(off_t, size_t, const UserOrKernelBuffer& data, FileDescription*) = 0;
     virtual KResultOr<NonnullRefPtr<Inode>> create_child(StringView name, mode_t, dev_t, uid_t, gid_t) = 0;
     virtual KResult add_child(Inode&, const StringView& name, mode_t) = 0;
diff --git a/Kernel/FileSystem/Plan9FileSystem.cpp b/Kernel/FileSystem/Plan9FileSystem.cpp
index 729182f39b..657ba67a5e 100644
--- a/Kernel/FileSystem/Plan9FileSystem.cpp
+++ b/Kernel/FileSystem/Plan9FileSystem.cpp
@@ -914,7 +914,7 @@ KResult Plan9FSInode::traverse_as_directory(Function<bool(FileSystem::DirectoryE
     }
 }
 
-RefPtr<Inode> Plan9FSInode::lookup(StringView name)
+KResultOr<NonnullRefPtr<Inode>> Plan9FSInode::lookup(StringView name)
 {
     u32 newfid = fs().allocate_fid();
     Plan9FS::Message message { fs(), Plan9FS::Message::Type::Twalk };
@@ -922,7 +922,7 @@ RefPtr<Inode> Plan9FSInode::lookup(StringView name)
     auto result = fs().post_message_and_wait_for_a_reply(message);
 
     if (result.is_error())
-        return nullptr;
+        return result;
 
     return Plan9FSInode::create(fs(), newfid);
 }
diff --git a/Kernel/FileSystem/Plan9FileSystem.h b/Kernel/FileSystem/Plan9FileSystem.h
index 3dbc699b0e..9301fca091 100644
--- a/Kernel/FileSystem/Plan9FileSystem.h
+++ b/Kernel/FileSystem/Plan9FileSystem.h
@@ -159,7 +159,7 @@ public:
     virtual KResultOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer& buffer, FileDescription*) const override;
     virtual KResultOr<size_t> write_bytes(off_t, size_t, const UserOrKernelBuffer& data, FileDescription*) override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual RefPtr<Inode> lookup(StringView name) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override;
     virtual KResultOr<NonnullRefPtr<Inode>> create_child(StringView name, mode_t, dev_t, uid_t, gid_t) override;
     virtual KResult add_child(Inode&, const StringView& name, mode_t) override;
     virtual KResult remove_child(const StringView& name) override;
diff --git a/Kernel/FileSystem/ProcFS.cpp b/Kernel/FileSystem/ProcFS.cpp
index e18fb1e92a..59c0864fe8 100644
--- a/Kernel/FileSystem/ProcFS.cpp
+++ b/Kernel/FileSystem/ProcFS.cpp
@@ -146,7 +146,7 @@ KResult ProcFSGlobalInode::traverse_as_directory(Function<bool(FileSystem::Direc
     VERIFY_NOT_REACHED();
 }
 
-RefPtr<Inode> ProcFSGlobalInode::lookup(StringView)
+KResultOr<NonnullRefPtr<Inode>> ProcFSGlobalInode::lookup(StringView)
 {
     VERIFY_NOT_REACHED();
 }
@@ -200,12 +200,12 @@ KResult ProcFSDirectoryInode::traverse_as_directory(Function<bool(FileSystem::Di
     return m_associated_component->traverse_as_directory(procfs().fsid(), move(callback));
 }
 
-RefPtr<Inode> ProcFSDirectoryInode::lookup(StringView name)
+KResultOr<NonnullRefPtr<Inode>> ProcFSDirectoryInode::lookup(StringView name)
 {
     MutexLocker locker(procfs().m_lock);
     auto component = m_associated_component->lookup(name);
     if (!component)
-        return {};
+        return ENOMEM;
     return component->to_inode(procfs());
 }
 
@@ -288,12 +288,12 @@ KResult ProcFSProcessDirectoryInode::traverse_as_directory(Function<bool(FileSys
     return process->traverse_as_directory(procfs().fsid(), move(callback));
 }
 
-RefPtr<Inode> ProcFSProcessDirectoryInode::lookup(StringView name)
+KResultOr<NonnullRefPtr<Inode>> ProcFSProcessDirectoryInode::lookup(StringView name)
 {
     MutexLocker locker(procfs().m_lock);
     auto process = Process::from_pid(associated_pid());
     if (!process)
-        return nullptr;
+        return ESRCH;
     if (name == "fd")
         return ProcFSProcessSubDirectoryInode::create(procfs(), SegmentedProcFSIndex::ProcessSubDirectory::FileDescriptions, associated_pid());
     if (name == "stacks")
@@ -314,7 +314,7 @@ RefPtr<Inode> ProcFSProcessDirectoryInode::lookup(StringView name)
         return ProcFSProcessPropertyInode::create_for_pid_property(procfs(), SegmentedProcFSIndex::MainProcessProperty::VirtualMemoryStats, associated_pid());
     if (name == "root")
         return ProcFSProcessPropertyInode::create_for_pid_property(procfs(), SegmentedProcFSIndex::MainProcessProperty::RootLink, associated_pid());
-    return nullptr;
+    return ENOENT;
 }
 
 NonnullRefPtr<ProcFSProcessSubDirectoryInode> ProcFSProcessSubDirectoryInode::create(const ProcFS& procfs, SegmentedProcFSIndex::ProcessSubDirectory sub_directory_type, ProcessID pid)
@@ -376,21 +376,26 @@ KResult ProcFSProcessSubDirectoryInode::traverse_as_directory(Function<bool(File
     VERIFY_NOT_REACHED();
 }
 
-RefPtr<Inode> ProcFSProcessSubDirectoryInode::lookup(StringView name)
+KResultOr<NonnullRefPtr<Inode>> ProcFSProcessSubDirectoryInode::lookup(StringView name)
 {
     MutexLocker locker(procfs().m_lock);
     auto process = Process::from_pid(associated_pid());
     if (!process)
-        return {};
+        return ESRCH;
+    RefPtr<Inode> inode;
     switch (m_sub_directory_type) {
     case SegmentedProcFSIndex::ProcessSubDirectory::FileDescriptions:
-        return process->lookup_file_descriptions_directory(procfs(), name);
+        inode = process->lookup_file_descriptions_directory(procfs(), name);
+        break;
     case SegmentedProcFSIndex::ProcessSubDirectory::Stacks:
-        return process->lookup_stacks_directory(procfs(), name);
+        inode = process->lookup_stacks_directory(procfs(), name);
+        break;
     default:
         VERIFY_NOT_REACHED();
     }
-    VERIFY_NOT_REACHED();
+    if (!inode)
+        return ENOENT;
+    return inode.release_nonnull();
 }
 
 NonnullRefPtr<ProcFSProcessPropertyInode> ProcFSProcessPropertyInode::create_for_file_description_link(const ProcFS& procfs, unsigned file_description_index, ProcessID pid)
@@ -514,9 +519,9 @@ KResultOr<size_t> ProcFSProcessPropertyInode::read_bytes(off_t offset, size_t co
 
     return nread;
 }
-RefPtr<Inode> ProcFSProcessPropertyInode::lookup(StringView)
+KResultOr<NonnullRefPtr<Inode>> ProcFSProcessPropertyInode::lookup(StringView)
 {
-    VERIFY_NOT_REACHED();
+    return EINVAL;
 }
 
 static KResult build_from_cached_data(KBufferBuilder& builder, ProcFSInodeData& cached_data)
diff --git a/Kernel/FileSystem/ProcFS.h b/Kernel/FileSystem/ProcFS.h
index 49b4d89b44..d03eb57c71 100644
--- a/Kernel/FileSystem/ProcFS.h
+++ b/Kernel/FileSystem/ProcFS.h
@@ -83,7 +83,7 @@ protected:
     virtual void did_seek(FileDescription&, off_t) override final;
     virtual InodeMetadata metadata() const override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual RefPtr<Inode> lookup(StringView) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView) override;
 
     NonnullRefPtr<ProcFSExposedComponent> m_associated_component;
 };
@@ -111,7 +111,7 @@ protected:
     // ^Inode
     virtual InodeMetadata metadata() const override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual RefPtr<Inode> lookup(StringView name) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override;
 };
 
 class ProcFSProcessAssociatedInode : public ProcFSInode {
@@ -142,7 +142,7 @@ private:
     virtual InodeMetadata metadata() const override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
     virtual KResultOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer& buffer, FileDescription*) const override final;
-    virtual RefPtr<Inode> lookup(StringView name) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override;
 };
 
 class ProcFSProcessSubDirectoryInode final : public ProcFSProcessAssociatedInode {
@@ -159,7 +159,7 @@ private:
     virtual InodeMetadata metadata() const override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
     virtual KResultOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer& buffer, FileDescription*) const override final;
-    virtual RefPtr<Inode> lookup(StringView name) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override;
 
     const SegmentedProcFSIndex::ProcessSubDirectory m_sub_directory_type;
 };
@@ -182,7 +182,7 @@ private:
     virtual InodeMetadata metadata() const override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
     virtual KResultOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer& buffer, FileDescription*) const override final;
-    virtual RefPtr<Inode> lookup(StringView name) override final;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override final;
 
     KResult refresh_data(FileDescription& description);
     KResult try_to_acquire_data(Process& process, KBufferBuilder& builder) const;
diff --git a/Kernel/FileSystem/SysFS.cpp b/Kernel/FileSystem/SysFS.cpp
index 677ba4baee..77488554c5 100644
--- a/Kernel/FileSystem/SysFS.cpp
+++ b/Kernel/FileSystem/SysFS.cpp
@@ -106,7 +106,7 @@ KResult SysFSInode::traverse_as_directory(Function<bool(FileSystem::DirectoryEnt
     VERIFY_NOT_REACHED();
 }
 
-RefPtr<Inode> SysFSInode::lookup(StringView)
+KResultOr<NonnullRefPtr<Inode>> SysFSInode::lookup(StringView)
 {
     VERIFY_NOT_REACHED();
 }
@@ -195,12 +195,12 @@ KResult SysFSDirectoryInode::traverse_as_directory(Function<bool(FileSystem::Dir
     return m_associated_component->traverse_as_directory(fs().fsid(), move(callback));
 }
 
-RefPtr<Inode> SysFSDirectoryInode::lookup(StringView name)
+KResultOr<NonnullRefPtr<Inode>> SysFSDirectoryInode::lookup(StringView name)
 {
     MutexLocker locker(fs().m_lock);
     auto component = m_associated_component->lookup(name);
     if (!component)
-        return {};
+        return ENOENT;
     return component->to_inode(fs());
 }
 
diff --git a/Kernel/FileSystem/SysFS.h b/Kernel/FileSystem/SysFS.h
index d52d6e77f3..836a0220c9 100644
--- a/Kernel/FileSystem/SysFS.h
+++ b/Kernel/FileSystem/SysFS.h
@@ -85,7 +85,7 @@ protected:
     SysFSInode(SysFS const&, SysFSComponent const&);
     virtual KResultOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer& buffer, FileDescription*) const override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual RefPtr<Inode> lookup(StringView name) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override;
     virtual void flush_metadata() override;
     virtual InodeMetadata metadata() const override;
     virtual KResultOr<size_t> write_bytes(off_t, size_t, UserOrKernelBuffer const&, FileDescription*) override;
@@ -114,7 +114,7 @@ protected:
     // ^Inode
     virtual InodeMetadata metadata() const override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual RefPtr<Inode> lookup(StringView name) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override;
 };
 
 }
diff --git a/Kernel/FileSystem/TmpFS.cpp b/Kernel/FileSystem/TmpFS.cpp
index 2cebe79013..ba62609c79 100644
--- a/Kernel/FileSystem/TmpFS.cpp
+++ b/Kernel/FileSystem/TmpFS.cpp
@@ -193,19 +193,24 @@ KResultOr<size_t> TmpFSInode::write_bytes(off_t offset, size_t size, const UserO
     return size;
 }
 
-RefPtr<Inode> TmpFSInode::lookup(StringView name)
+KResultOr<NonnullRefPtr<Inode>> TmpFSInode::lookup(StringView name)
 {
     MutexLocker locker(m_inode_lock, Mutex::Mode::Shared);
     VERIFY(is_directory());
 
     if (name == ".")
-        return this;
-    if (name == "..")
-        return fs().get_inode(m_parent);
+        return *this;
+    if (name == "..") {
+        auto inode = fs().get_inode(m_parent);
+        // FIXME: If this cannot fail, we should probably VERIFY here instead.
+        if (!inode)
+            return ENOENT;
+        return inode.release_nonnull();
+    }
 
     auto* child = find_child_by_name(name);
     if (!child)
-        return {};
+        return ENOENT;
     return child->inode;
 }
 
diff --git a/Kernel/FileSystem/TmpFS.h b/Kernel/FileSystem/TmpFS.h
index 31edcbae3f..9aa96aea18 100644
--- a/Kernel/FileSystem/TmpFS.h
+++ b/Kernel/FileSystem/TmpFS.h
@@ -55,7 +55,7 @@ public:
     virtual KResultOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer& buffer, FileDescription*) const override;
     virtual InodeMetadata metadata() const override;
     virtual KResult traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual RefPtr<Inode> lookup(StringView name) override;
+    virtual KResultOr<NonnullRefPtr<Inode>> lookup(StringView name) override;
     virtual void flush_metadata() override;
     virtual KResultOr<size_t> write_bytes(off_t, size_t, const UserOrKernelBuffer& buffer, FileDescription*) override;
     virtual KResultOr<NonnullRefPtr<Inode>> create_child(StringView name, mode_t, dev_t, uid_t, gid_t) override;
diff --git a/Kernel/FileSystem/VirtualFileSystem.cpp b/Kernel/FileSystem/VirtualFileSystem.cpp
index 4a0152918e..df338469ce 100644
--- a/Kernel/FileSystem/VirtualFileSystem.cpp
+++ b/Kernel/FileSystem/VirtualFileSystem.cpp
@@ -965,16 +965,17 @@ KResultOr<NonnullRefPtr<Custody>> VirtualFileSystem::resolve_path_without_veil(S
         }
 
         // Okay, let's look up this part.
-        auto child_inode = parent.inode().lookup(part);
-        if (!child_inode) {
+        auto child_or_error = parent.inode().lookup(part);
+        if (child_or_error.is_error()) {
             if (out_parent) {
                 // ENOENT with a non-null parent custody signals to caller that
                 // we found the immediate parent of the file, but the file itself
                 // does not exist yet.
                 *out_parent = have_more_parts ? nullptr : &parent;
             }
-            return ENOENT;
+            return child_or_error.error();
         }
+        auto child_inode = child_or_error.release_value();
 
         int mount_flags_for_child = parent.mount_flags();