Add a "pwd" utility to userland.

It's implemented as a separate process. How cute is that.
Tasks now have a current working directory. Spawned tasks inherit their
parent task's working directory.
Currently everyone just uses "/" as there's no way to chdir().

VirtualFileSystem/FileHandle.cpp

@@ -142,6 +142,9 @@ ssize_t FileHandle::get_dir_entries(byte* buffer, size_t size)
         return true;
     });
 
+    if (size < stream.offset())
+        return -1;
+
     memcpy(buffer, tempBuffer.pointer(), stream.offset());
     return stream.offset();
 }

VirtualFileSystem/FileHandle.h

@@ -16,6 +16,8 @@ public:
 
     ByteBuffer readEntireFile();
 
+    String absolutePath() const;
+
 #ifdef SERENITY
     int fd() const { return m_fd; }
     void setFD(int fd) { m_fd = fd; }

VirtualFileSystem/InodeIdentifier.h

@@ -28,6 +28,11 @@ public:
         return m_fileSystemID == other.m_fileSystemID && m_index == other.m_index;
     }
 
+    bool operator!=(const InodeIdentifier& other) const
+    {
+        return m_fileSystemID != other.m_fileSystemID || m_index != other.m_index;
+    }
+
     InodeMetadata metadata() const;
     bool isRootInode() const;
 

VirtualFileSystem/VirtualFileSystem.h

@@ -78,6 +78,7 @@ private:
     friend class FileHandle;
 
     void enumerateDirectoryInode(InodeIdentifier, Function<bool(const FileSystem::DirectoryEntry&)>);
+    String absolutePath(InodeIdentifier);
     InodeIdentifier resolvePath(const String& path);
     InodeIdentifier resolveSymbolicLink(const String& basePath, InodeIdentifier symlinkInode);