Kernel: Make Memory::Region allocation functions return KResultOr

This makes for some nicer handling of errors compared to checking an
OwnPtr for null state.

Kernel/Memory/AddressSpace.cpp

@@ -149,11 +149,11 @@ Optional<VirtualRange> AddressSpace::allocate_range(VirtualAddress vaddr, size_t
 
 KResultOr<Region*> AddressSpace::try_allocate_split_region(Region const& source_region, VirtualRange const& range, size_t offset_in_vmobject)
 {
-    auto new_region = Region::try_create_user_accessible(
+    auto maybe_new_region = Region::try_create_user_accessible(
         range, source_region.vmobject(), offset_in_vmobject, KString::try_create(source_region.name()), source_region.access(), source_region.is_cacheable() ? Region::Cacheable::Yes : Region::Cacheable::No, source_region.is_shared());
-    if (!new_region)
-        return ENOMEM;
-    auto* region = add_region(new_region.release_nonnull());
+    if (maybe_new_region.is_error())
+        return maybe_new_region.error();
+    auto* region = add_region(maybe_new_region.release_value());
     if (!region)
         return ENOMEM;
     region->set_syscall_region(source_region.is_syscall_region());
@@ -173,12 +173,14 @@ KResultOr<Region*> AddressSpace::allocate_region(VirtualRange const& range, Stri
     auto maybe_vmobject = AnonymousVMObject::try_create_with_size(range.size(), strategy);
     if (maybe_vmobject.is_error())
         return maybe_vmobject.error();
-    auto region = Region::try_create_user_accessible(range, maybe_vmobject.release_value(), 0, KString::try_create(name), prot_to_region_access_flags(prot), Region::Cacheable::Yes, false);
-    if (!region)
-        return ENOMEM;
+    auto maybe_region = Region::try_create_user_accessible(range, maybe_vmobject.release_value(), 0, KString::try_create(name), prot_to_region_access_flags(prot), Region::Cacheable::Yes, false);
+    if (maybe_region.is_error())
+        return maybe_region.error();
+
+    auto region = maybe_region.release_value();
     if (!region->map(page_directory()))
         return ENOMEM;
-    auto* added_region = add_region(region.release_nonnull());
+    auto* added_region = add_region(move(region));
     if (!added_region)
         return ENOMEM;
     return added_region;
@@ -201,12 +203,12 @@ KResultOr<Region*> AddressSpace::allocate_region_with_vmobject(VirtualRange cons
         return EINVAL;
     }
     offset_in_vmobject &= PAGE_MASK;
-    auto region = Region::try_create_user_accessible(range, move(vmobject), offset_in_vmobject, KString::try_create(name), prot_to_region_access_flags(prot), Region::Cacheable::Yes, shared);
-    if (!region) {
+    auto maybe_region = Region::try_create_user_accessible(range, move(vmobject), offset_in_vmobject, KString::try_create(name), prot_to_region_access_flags(prot), Region::Cacheable::Yes, shared);
+    if (maybe_region.is_error()) {
         dbgln("allocate_region_with_vmobject: Unable to allocate Region");
-        return ENOMEM;
+        return maybe_region.error();
     }
-    auto* added_region = add_region(region.release_nonnull());
+    auto* added_region = add_region(maybe_region.release_value());
     if (!added_region)
         return ENOMEM;
     if (!added_region->map(page_directory()))

Kernel/Memory/MemoryManager.cpp

@@ -743,9 +743,12 @@ OwnPtr<Region> MemoryManager::allocate_kernel_region(PhysicalAddress paddr, size
 
 OwnPtr<Region> MemoryManager::allocate_kernel_region_with_vmobject(VirtualRange const& range, VMObject& vmobject, StringView name, Region::Access access, Region::Cacheable cacheable)
 {
-    auto region = Region::try_create_kernel_only(range, vmobject, 0, KString::try_create(name), access, cacheable);
-    if (region)
-        region->map(kernel_page_directory());
+    auto maybe_region = Region::try_create_kernel_only(range, vmobject, 0, KString::try_create(name), access, cacheable);
+    if (maybe_region.is_error())
+        return {};
+
+    auto region = maybe_region.release_value();
+    region->map(kernel_page_directory());
     return region;
 }
 

Kernel/Memory/Region.cpp

@@ -50,7 +50,7 @@ Region::~Region()
     }
 }
 
-OwnPtr<Region> Region::clone()
+KResultOr<NonnullOwnPtr<Region>> Region::try_clone()
 {
     VERIFY(Process::current());
 
@@ -60,12 +60,14 @@ OwnPtr<Region> Region::clone()
             VERIFY(vmobject().is_shared_inode());
 
         // Create a new region backed by the same VMObject.
-        auto region = Region::try_create_user_accessible(
+        auto maybe_region = Region::try_create_user_accessible(
             m_range, m_vmobject, m_offset_in_vmobject, m_name ? m_name->try_clone() : OwnPtr<KString> {}, access(), m_cacheable ? Cacheable::Yes : Cacheable::No, m_shared);
-        if (!region) {
+        if (maybe_region.is_error()) {
             dbgln("Region::clone: Unable to allocate new Region");
-            return nullptr;
+            return maybe_region.error();
         }
+
+        auto region = maybe_region.release_value();
         region->set_mmap(m_mmap);
         region->set_shared(m_shared);
         region->set_syscall_region(is_syscall_region());
@@ -77,16 +79,19 @@ OwnPtr<Region> Region::clone()
 
     auto maybe_vmobject_clone = vmobject().try_clone();
     if (maybe_vmobject_clone.is_error())
-        return {};
+        return maybe_vmobject_clone.error();
+    auto vmobject_clone = maybe_vmobject_clone.release_value();
 
     // Set up a COW region. The parent (this) region becomes COW as well!
     remap();
-    auto clone_region = Region::try_create_user_accessible(
-        m_range, maybe_vmobject_clone.release_value(), m_offset_in_vmobject, m_name ? m_name->try_clone() : OwnPtr<KString> {}, access(), m_cacheable ? Cacheable::Yes : Cacheable::No, m_shared);
-    if (!clone_region) {
+    auto maybe_clone_region = Region::try_create_user_accessible(
+        m_range, vmobject_clone, m_offset_in_vmobject, m_name ? m_name->try_clone() : OwnPtr<KString> {}, access(), m_cacheable ? Cacheable::Yes : Cacheable::No, m_shared);
+    if (maybe_clone_region.is_error()) {
         dbgln("Region::clone: Unable to allocate new Region for COW");
-        return nullptr;
+        return maybe_clone_region.error();
     }
+    auto clone_region = maybe_clone_region.release_value();
+
     if (m_stack) {
         VERIFY(is_readable());
         VERIFY(is_writable());
@@ -143,17 +148,14 @@ size_t Region::amount_shared() const
     return bytes;
 }
 
-OwnPtr<Region> Region::try_create_user_accessible(VirtualRange const& range, NonnullRefPtr<VMObject> vmobject, size_t offset_in_vmobject, OwnPtr<KString> name, Region::Access access, Cacheable cacheable, bool shared)
+KResultOr<NonnullOwnPtr<Region>> Region::try_create_user_accessible(VirtualRange const& range, NonnullRefPtr<VMObject> vmobject, size_t offset_in_vmobject, OwnPtr<KString> name, Region::Access access, Cacheable cacheable, bool shared)
 {
-    auto region = adopt_own_if_nonnull(new (nothrow) Region(range, move(vmobject), offset_in_vmobject, move(name), access, cacheable, shared));
-    if (!region)
-        return nullptr;
-    return region;
+    return adopt_nonnull_own_or_enomem(new (nothrow) Region(range, move(vmobject), offset_in_vmobject, move(name), access, cacheable, shared));
 }
 
-OwnPtr<Region> Region::try_create_kernel_only(VirtualRange const& range, NonnullRefPtr<VMObject> vmobject, size_t offset_in_vmobject, OwnPtr<KString> name, Region::Access access, Cacheable cacheable)
+KResultOr<NonnullOwnPtr<Region>> Region::try_create_kernel_only(VirtualRange const& range, NonnullRefPtr<VMObject> vmobject, size_t offset_in_vmobject, OwnPtr<KString> name, Region::Access access, Cacheable cacheable)
 {
-    return adopt_own_if_nonnull(new (nothrow) Region(range, move(vmobject), offset_in_vmobject, move(name), access, cacheable, false));
+    return adopt_nonnull_own_or_enomem(new (nothrow) Region(range, move(vmobject), offset_in_vmobject, move(name), access, cacheable, false));
 }
 
 bool Region::should_cow(size_t page_index) const

Kernel/Memory/Region.h

@@ -49,8 +49,8 @@ public:
         Yes,
     };
 
-    static OwnPtr<Region> try_create_user_accessible(VirtualRange const&, NonnullRefPtr<VMObject>, size_t offset_in_vmobject, OwnPtr<KString> name, Region::Access access, Cacheable, bool shared);
-    static OwnPtr<Region> try_create_kernel_only(VirtualRange const&, NonnullRefPtr<VMObject>, size_t offset_in_vmobject, OwnPtr<KString> name, Region::Access access, Cacheable = Cacheable::Yes);
+    static KResultOr<NonnullOwnPtr<Region>> try_create_user_accessible(VirtualRange const&, NonnullRefPtr<VMObject>, size_t offset_in_vmobject, OwnPtr<KString> name, Region::Access access, Cacheable, bool shared);
+    static KResultOr<NonnullOwnPtr<Region>> try_create_kernel_only(VirtualRange const&, NonnullRefPtr<VMObject>, size_t offset_in_vmobject, OwnPtr<KString> name, Region::Access access, Cacheable = Cacheable::Yes);
 
     ~Region();
 
@@ -90,7 +90,7 @@ public:
 
     PageFaultResponse handle_fault(PageFault const&);
 
-    OwnPtr<Region> clone();
+    KResultOr<NonnullOwnPtr<Region>> try_clone();
 
     bool contains(VirtualAddress vaddr) const
     {

Kernel/Syscalls/fork.cpp

@@ -96,14 +96,14 @@ KResultOr<FlatPtr> Process::sys$fork(RegisterState& regs)
         ScopedSpinLock lock(address_space().get_lock());
         for (auto& region : address_space().regions()) {
             dbgln_if(FORK_DEBUG, "fork: cloning Region({}) '{}' @ {}", region, region->name(), region->vaddr());
-            auto region_clone = region->clone();
-            if (!region_clone) {
+            auto maybe_region_clone = region->try_clone();
+            if (maybe_region_clone.is_error()) {
                 dbgln("fork: Cannot clone region, insufficient memory");
                 // TODO: tear down new process?
-                return ENOMEM;
+                return maybe_region_clone.error();
             }
 
-            auto* child_region = child->address_space().add_region(region_clone.release_nonnull());
+            auto* child_region = child->address_space().add_region(maybe_region_clone.release_value());
             if (!child_region) {
                 dbgln("fork: Cannot add region, insufficient memory");
                 // TODO: tear down new process?