Add gettid

Cargo.toml

@@ -20,7 +20,7 @@ preadv_pwritev = []
 signalfd = []
 
 [dependencies]
-libc     = "0.2.7"
+libc     = "0.2.8"
 bitflags = "0.4"
 cfg-if = "0.1.0"
 

src/unistd.rs

@@ -56,6 +56,12 @@ pub fn setpgid(pid: pid_t, pgid: pid_t) -> Result<()> {
     Errno::result(res).map(drop)
 }
 
+#[cfg(target_os = "linux")]
+#[inline]
+pub fn gettid() -> pid_t {
+    unsafe { libc::syscall(libc::SYS_gettid) as pid_t }    // no error handling, according to man page: "These functions are always successful."
+}
+
 #[inline]
 pub fn dup(oldfd: RawFd) -> Result<RawFd> {
     let res = unsafe { libc::dup(oldfd) };

test/test_unistd.rs

@@ -54,6 +54,13 @@ fn test_getpid() {
     assert!(ppid > 0);
 }
 
+#[cfg(target_os = "linux")]
+#[test]
+fn test_gettid() {
+    let tid = gettid();
+    assert!(tid > 0);
+}
+
 macro_rules! execve_test_factory(
     ($test_name:ident, $syscall:ident, $unix_sh:expr, $android_sh:expr) => (
     #[test]