sys_util: fix handling EINTR of C system functions

System functions have 2 ways of signalling errors, either via returning
-1 as result, and setting errno, or directly returning error code, and
we can not distinguish automatically between the 2 options when using
InterruptibleResult trait for i32 values.

Let's remove this trait for i32 and create 2 explicit macros:
handle_eintr_rc and handle_eintr_errno.

TEST=cargo test --features plugin; cargo test -p sys_util
BUG=None

Change-Id: I1dc8e3c023e7bf7875ac3536703eb71fa3206b7b
Signed-off-by: Dmitry Torokhov <dtor@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/940612
Reviewed-by: Zach Reizner <zachr@chromium.org>

sys_util/src/errno.rs

@@ -57,3 +57,13 @@ impl Display for Error {
 pub fn errno_result<T>() -> Result<T> {
     Err(Error::last())
 }
+
+/// Sets errno to given error code.
+/// Only defined when we compile tests as normal code does not
+/// normally need set errno.
+#[cfg(test)]
+pub fn set_errno(e: i32) {
+    unsafe {
+        *__errno_location() = e;
+    }
+}

sys_util/src/handle_eintr.rs

@@ -15,12 +15,6 @@ pub trait InterruptibleResult {
     fn is_interrupted(&self) -> bool;
 }
 
-impl InterruptibleResult for i32 {
-    fn is_interrupted(&self) -> bool {
-        *self == EINTR
-    }
-}
-
 impl<T> InterruptibleResult for ::Result<T> {
     fn is_interrupted(&self) -> bool {
         match self {
@@ -40,15 +34,17 @@ impl<T> InterruptibleResult for io::Result<T> {
 }
 
 /// Macro that retries the given expression every time its result indicates it was interrupted (i.e.
-/// returned `-EINTR`). This is useful for operations that are prone to being interrupted by
+/// returned `EINTR`). This is useful for operations that are prone to being interrupted by
 /// signals, such as blocking syscalls.
 ///
 /// The given expression `$x` can return
 ///
-/// * `i32` in which case the expression is retried if equal to `EINTR`.
 /// * `sys_util::Result` in which case the expression is retried if the `Error::errno()` is `EINTR`.
 /// * `std::io::Result` in which case the expression is retried if the `ErrorKind` is `ErrorKind::Interrupted`.
 ///
+/// Note that if expression returns i32 (i.e. either -1 or error code), then handle_eintr_errno()
+/// or handle_eintr_rc() should be used instead.
+///
 /// In all cases where the result does not indicate that the expression was interrupted, the result
 /// is returned verbatim to the caller of this macro.
 ///
@@ -142,27 +138,84 @@ macro_rules! handle_eintr {
     )
 }
 
+/// Macro that retries the given expression every time its result indicates it was interrupted.
+/// It is intended to use with system functions that return `EINTR` and other error codes
+/// directly as their result.
+/// Most of reentrant functions use this way of signalling errors.
+#[macro_export]
+macro_rules! handle_eintr_rc {
+    ($x:expr) => (
+        {
+            use libc::EINTR;
+            let mut res;
+            loop {
+                res = $x;
+                if res != EINTR {
+                    break;
+                }
+            }
+            res
+        }
+    )
+}
+
+/// Macro that retries the given expression every time its result indicates it was interrupted.
+/// It is intended to use with system functions that signal error by returning `-1` and setting
+/// `errno` to appropriate error code (`EINTR`, `EINVAL`, etc.)
+/// Most of standard non-reentrant libc functions use this way of signalling errors.
+#[macro_export]
+macro_rules! handle_eintr_errno {
+    ($x:expr) => (
+        {
+            use $crate::Error;
+            use libc::EINTR;
+            let mut res;
+            loop {
+                res = $x;
+                if res != -1 || Error::last() != Error::new(EINTR) {
+                    break;
+                }
+            }
+            res
+        }
+    )
+}
 
 #[cfg(test)]
 mod tests {
     use super::*;
+    use errno::set_errno;
 
     use Error as SysError;
 
     #[test]
-    fn i32_eintr() {
+    fn i32_eintr_rc() {
         let mut count = 3;
         {
             let mut dummy = || {
                 count -= 1;
                 if count > 0 { EINTR } else { 0 }
             };
-            let res = handle_eintr!(dummy());
+            let res = handle_eintr_rc!(dummy());
             assert_eq!(res, 0);
         }
         assert_eq!(count, 0);
     }
 
+    #[test]
+    fn i32_eintr_errno() {
+        let mut count = 3;
+        {
+            let mut dummy = || {
+                count -= 1;
+                if count > 0 { set_errno(EINTR); -1 } else { 56 }
+            };
+            let res = handle_eintr_errno!(dummy());
+            assert_eq!(res, 56);
+        }
+        assert_eq!(count, 0);
+    }
+
     #[test]
     fn sys_eintr() {
         let mut count = 7;

sys_util/src/passwd.rs

@@ -29,11 +29,11 @@ pub fn get_user_id(user_name: &CStr) -> Result<uid_t> {
     // This call is safe as long as it behaves as described in the man page. We pass in valid
     // pointers to stack-allocated buffers, and the length check for the scratch buffer is correct.
     unsafe {
-        handle_eintr!(getpwnam_r(user_name.as_ptr(),
-                                 &mut passwd,
-                                 buf.as_mut_ptr(),
-                                 buf.len(),
-                                 &mut passwd_result))
+        handle_eintr_rc!(getpwnam_r(user_name.as_ptr(),
+                                    &mut passwd,
+                                    buf.as_mut_ptr(),
+                                    buf.len(),
+                                    &mut passwd_result))
     };
 
     if passwd_result.is_null() {
@@ -59,11 +59,11 @@ pub fn get_group_id(group_name: &CStr) -> Result<gid_t> {
     // This call is safe as long as it behaves as described in the man page. We pass in valid
     // pointers to stack-allocated buffers, and the length check for the scratch buffer is correct.
     unsafe {
-        handle_eintr!(getgrnam_r(group_name.as_ptr(),
-                                 &mut group,
-                                 buf.as_mut_ptr(),
-                                 buf.len(),
-                                 &mut group_result))
+        handle_eintr_rc!(getgrnam_r(group_name.as_ptr(),
+                                    &mut group,
+                                    buf.as_mut_ptr(),
+                                    buf.len(),
+                                    &mut group_result))
     };
 
     if group_result.is_null() {

sys_util/src/poll.rs

@@ -115,11 +115,11 @@ impl Poller {
         // Safe because poll is given the correct length of properly initialized pollfds, and we
         // check the return result.
         let ret = unsafe {
-            handle_eintr!(ppoll(self.pollfds.as_mut_ptr(),
-                                self.pollfds.len() as nfds_t,
-                                &mut timeout_spec,
-                                null(),
-                                0))
+            handle_eintr_errno!(ppoll(self.pollfds.as_mut_ptr(),
+                                      self.pollfds.len() as nfds_t,
+                                      &mut timeout_spec,
+                                      null(),
+                                      0))
         };
 
         *timeout = Duration::new(timeout_spec.tv_sec as u64, timeout_spec.tv_nsec as u32);