Kernel: Implement basic F_{GET,SET}LK{,W}

At the moment these lock the whole file which is not what is supposed to
happen. Some port was trying to use these and this seems to work for
that. This may cause deadlocks but that should be easy enough to find
the reason because of the debug warnings

kernel/kernel/OpenFileDescriptorSet.cpp

@@ -252,6 +252,46 @@ namespace Kernel
 				m_open_files[fd].status_flags() &= O_ACCMODE;
 				m_open_files[fd].status_flags() |= extra;
 				return 0;
+			case F_GETLK:
+			{
+				dwarnln("TODO: proper fcntl F_GETLK");
+
+				auto* param = reinterpret_cast<struct flock*>(extra);
+				const auto& flock = m_open_files[fd].description->flock;
+
+				if (flock.lockers.empty())
+					param->l_type = F_UNLCK;
+				else
+				{
+					*param = {
+						.l_type = static_cast<short>(flock.shared ? F_RDLCK : F_WRLCK),
+						.l_whence = SEEK_SET,
+						.l_start = 0,
+						.l_len = 1,
+						.l_pid = *flock.lockers.begin(),
+					};
+				}
+
+				return 0;
+			}
+			case F_SETLK:
+			case F_SETLKW:
+			{
+				dwarnln("TODO: proper fcntl F_SETLK(W)");
+
+				int op = cmd == F_SETLKW ? LOCK_NB : 0;
+				switch (reinterpret_cast<const struct flock*>(extra)->l_type)
+				{
+					case F_UNLCK: op |= LOCK_UN; break;
+					case F_RDLCK: op |= LOCK_SH; break;
+					case F_WRLCK: op |= LOCK_EX; break;
+					default:
+						return BAN::Error::from_errno(EINVAL);
+				}
+				TRY(flock(fd, op));
+
+				return 0;
+			}
 			default:
 				break;
 		}