Implement improved feature detection on Linux

Author: carllerche

src/features.rs

@@ -2,14 +2,99 @@ pub use self::os::*;
 
 #[cfg(target_os = "linux")]
 mod os {
-    pub fn atomic_cloexec() -> bool {
-        true // TODO: Not on all kernel versions
+    use sys::utsname::uname;
+
+    // Features:
+    // * atomic cloexec on socket: 2.6.27
+    // * pipe2: 2.6.27
+    // * accept4: 2.6.28
+
+    static VERS_UNKNOWN: uint = 1;
+    static VERS_2_6_18:  uint = 2;
+    static VERS_2_6_27:  uint = 3;
+    static VERS_2_6_28:  uint = 4;
+    static VERS_3:       uint = 5;
+
+    fn parse_kernel_version() -> uint {
+        let u = uname();
+
+        #[inline]
+        fn digit(dst: &mut uint, b: u8) {
+            *dst *= 10;
+            *dst += (b - b'0') as uint;
+        }
+
+        let mut curr = 0u;
+        let mut major = 0;
+        let mut minor = 0;
+        let mut patch = 0;
+
+        for b in u.release().bytes() {
+            if curr >= 3 {
+                break;
+            }
+
+            match b {
+                b'.' | b'-' => {
+                    curr += 1;
+                }
+                b'0'...b'9' => {
+                    match curr {
+                        0 => digit(&mut major, b),
+                        1 => digit(&mut minor, b),
+                        _ => digit(&mut patch, b),
+                    }
+                }
+                _ => break,
+            }
+        }
+
+        if major >= 3 {
+            VERS_3
+        } else if major >= 2 {
+            if minor >= 7 {
+                VERS_UNKNOWN
+            } else if minor >= 6 {
+                if patch >= 28 {
+                    VERS_2_6_28
+                } else if patch >= 27 {
+                    VERS_2_6_27
+                } else {
+                    VERS_2_6_18
+                }
+            } else {
+                VERS_UNKNOWN
+            }
+        } else {
+            VERS_UNKNOWN
+        }
+    }
+
+    fn kernel_version() -> uint {
+        static mut KERNEL_VERS: uint = 0;
+
+        unsafe {
+            if KERNEL_VERS == 0 {
+                KERNEL_VERS = parse_kernel_version();
+            }
+
+            KERNEL_VERS
+        }
+    }
+
+    pub fn socket_atomic_cloexec() -> bool {
+        kernel_version() >= VERS_2_6_27
+    }
+
+    #[test]
+    pub fn test_parsing_kernel_version() {
+        assert!(kernel_version() > 0);
     }
 }
 
 #[cfg(any(target_os = "macos", target_os = "ios"))]
 mod os {
-    pub fn atomic_cloexec() -> bool {
+    pub fn socket_atomic_cloexec() -> bool {
         false
     }
 }

src/sys/socket.rs

@@ -162,7 +162,7 @@ mod consts {
 }
 
 pub fn socket(domain: AddressFamily, mut ty: SockType, flags: SockFlag) -> SysResult<Fd> {
-    let feat_atomic = features::atomic_cloexec();
+    let feat_atomic = features::socket_atomic_cloexec();
 
     if feat_atomic {
         ty = ty | flags.bits();