Kernel: Factor out range allocation from Process::allocate_region*().

These functions were doing exactly the same thing for range allocation, so
share that code in an allocate_range() helper.

Region allocation will now also fail if range allocation fails, which means
that mmap() can actually fail without falling apart. Exciting times!

Kernel/FileSystem/FileDescriptor.cpp

@@ -346,6 +346,8 @@ KResultOr<Region*> FileDescriptor::mmap(Process& process, LinearAddress laddr, s
     // FIXME: Implement mapping at a client-specified address. Most of the support is already in plcae.
     ASSERT(laddr.as_ptr() == nullptr);
     auto* region = process.allocate_file_backed_region(LinearAddress(), size, inode(), move(region_name), prot & PROT_READ, prot & PROT_WRITE);
+    if (!region)
+        return KResult(-ENOMEM);
     region->page_in();
     return region;
 }

Kernel/Process.cpp

@@ -68,17 +68,20 @@ bool Process::in_group(gid_t gid) const
     return m_gids.contains(gid);
 }
 
-Region* Process::allocate_region(LinearAddress laddr, size_t size, String&& name, bool is_readable, bool is_writable, bool commit)
+Range Process::allocate_range(LinearAddress laddr, size_t size)
 {
     laddr.mask(PAGE_MASK);
     size = PAGE_ROUND_UP(size);
-
-    Range range;
     if (laddr.is_null())
-        range = m_range_allocator.allocate_anywhere(size);
+        return m_range_allocator.allocate_anywhere(size);
-    else
+    return m_range_allocator.allocate_specific(laddr, size);
-        range = m_range_allocator.allocate_specific(laddr, size);
+}
 
+Region* Process::allocate_region(LinearAddress laddr, size_t size, String&& name, bool is_readable, bool is_writable, bool commit)
+{
+    auto range = allocate_range(laddr, size);
+    if (!range.is_valid())
+        return nullptr;
     m_regions.append(adopt(*new Region(range, move(name), is_readable, is_writable)));
     MM.map_region(*this, *m_regions.last());
     if (commit)
@@ -88,15 +91,9 @@ Region* Process::allocate_region(LinearAddress laddr, size_t size, String&& name
 
 Region* Process::allocate_file_backed_region(LinearAddress laddr, size_t size, RetainPtr<Inode>&& inode, String&& name, bool is_readable, bool is_writable)
 {
-    laddr.mask(PAGE_MASK);
+    auto range = allocate_range(laddr, size);
-    size = PAGE_ROUND_UP(size);
+    if (!range.is_valid())
-
+        return nullptr;
-    Range range;
-    if (laddr.is_null())
-        range = m_range_allocator.allocate_anywhere(size);
-    else
-        range = m_range_allocator.allocate_specific(laddr, size);
-
     m_regions.append(adopt(*new Region(range, move(inode), move(name), is_readable, is_writable)));
     MM.map_region(*this, *m_regions.last());
     return m_regions.last().ptr();
@@ -104,15 +101,9 @@ Region* Process::allocate_file_backed_region(LinearAddress laddr, size_t size, R
 
 Region* Process::allocate_region_with_vmo(LinearAddress laddr, size_t size, Retained<VMObject>&& vmo, size_t offset_in_vmo, String&& name, bool is_readable, bool is_writable)
 {
-    laddr.mask(PAGE_MASK);
+    auto range = allocate_range(laddr, size);
-    size = PAGE_ROUND_UP(size);
+    if (!range.is_valid())
-
+        return nullptr;
-    Range range;
-    if (laddr.is_null())
-        range = m_range_allocator.allocate_anywhere(size);
-    else
-        range = m_range_allocator.allocate_specific(laddr, size);
-
     offset_in_vmo &= PAGE_MASK;
     size = ceil_div(size, PAGE_SIZE) * PAGE_SIZE;
     m_regions.append(adopt(*new Region(range, move(vmo), offset_in_vmo, move(name), is_readable, is_writable)));
@@ -328,6 +319,7 @@ int Process::do_exec(String path, Vector<String> arguments, Vector<String> envir
     vmo->set_name("ELF image");
 #endif
     RetainPtr<Region> region = allocate_region_with_vmo(LinearAddress(), descriptor->metadata().size, vmo.copy_ref(), 0, "executable", true, false);
+    ASSERT(region);
 
     if (this != &current->process()) {
         // FIXME: Don't force-load the entire executable at once, let the on-demand pager take care of it.

Kernel/Process.h

@@ -258,6 +258,8 @@ private:
 
     Process(String&& name, uid_t, gid_t, pid_t ppid, RingLevel, RetainPtr<Inode>&& cwd = nullptr, RetainPtr<Inode>&& executable = nullptr, TTY* = nullptr, Process* fork_parent = nullptr);
 
+    Range allocate_range(LinearAddress, size_t);
+
     int do_exec(String path, Vector<String> arguments, Vector<String> environment);
     ssize_t do_write(FileDescriptor&, const byte*, int data_size);