Implement the typical use of waitpid

kernel/syscall/error.rs

@@ -0,0 +1,28 @@
+/// The error number for an invalid value
+/// See http://www-numi.fnal.gov/offline_software/srt_public_context/WebDocs/Errors/unix_system_errors.html for numbers
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+#[repr(C)]
+pub enum Error {
+    /// Operation not permitted
+    NotPermitted = 1,
+    /// No such file or directory
+    NoEntry = 2,
+    /// No such process
+    NoProcess = 3,
+    /// Invalid executable format
+    NoExec = 8,
+    /// Bad file number
+    BadFile = 9,
+    /// Try again
+    TryAgain = 11,
+    /// File exists
+    FileExists = 17,
+    /// Invalid argument
+    InvalidValue = 22,
+    /// Too many open files
+    TooManyFiles = 24,
+    /// Syscall not implemented
+    NoCall = 38
+}
+
+pub type Result<T> = ::core::result::Result<T, Error>;