Skip the mount tests on kernel 4.4.0

Some versions of that kernel have a known bug with tmpfs in namespaces.
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1659087

Fixes #610

Author: asomers

test/test_mount.rs

@@ -21,6 +21,7 @@ mod test_mount {
     use nix::sched::{unshare, CLONE_NEWNS, CLONE_NEWUSER};
     use nix::sys::stat::{self, S_IRWXU, S_IRWXG, S_IRWXO, S_IXUSR, S_IXGRP, S_IXOTH};
     use nix::unistd::getuid;
+    use nix::sys::utsname;
 
     use tempdir::TempDir;
 
@@ -30,6 +31,20 @@ exit 23";
     const EXPECTED_STATUS: i32 = 23;
 
     const NONE: Option<&'static [u8]> = None;
+
+    // Skip tests on kernel 4.4.0, which has a bug regarding tmpfs in namespaces
+    // https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1659087
+    pub fn check_kernel() {
+	let u = utsname::uname();
+	if u.release().starts_with("4.4.0") {
+	    let stderr = io::stderr();
+	    let mut handle = stderr.lock();
+            writeln!(handle, "Linux kernel 4.4.0 has known bugs with tmpfs in namespaces.  Skipping test.")
+	        .unwrap();
+            process::exit(0);
+	}
+    }
+
     pub fn test_mount_tmpfs_without_flags_allows_rwx() {
         let tempdir = TempDir::new("nix-test_mount")
                           .unwrap_or_else(|e| panic!("tempdir failed: {}", e));
@@ -185,6 +200,7 @@ exit 23";
             .write(true)
             .open("/proc/self/uid_map")
             .and_then(|mut f| f.write(format!("1000 {} 1\n", uid).as_bytes()))
+            //.and_then(|mut f| f.write(format!("1000 {} 1\n", uid).as_bytes()))
             .unwrap_or_else(|e| panic!("could not write uid map: {}", e));
     }
 }
@@ -209,9 +225,12 @@ macro_rules! run_tests {
 
 #[cfg(target_os = "linux")]
 fn main() {
-    use test_mount::{setup_namespaces, test_mount_tmpfs_without_flags_allows_rwx,
-                     test_mount_rdonly_disallows_write, test_mount_noexec_disallows_exec,
+    use test_mount::{setup_namespaces, check_kernel,
+                     test_mount_tmpfs_without_flags_allows_rwx,
+                     test_mount_rdonly_disallows_write,
+                     test_mount_noexec_disallows_exec,
                      test_mount_bind};
+    check_kernel();
     setup_namespaces();
 
     run_tests!(test_mount_tmpfs_without_flags_allows_rwx,