Add LioCb::listio_resubmit

It helps deal with errors like EAGAIN, which can result in a subset of
an LioCb's operations being queued.

src/sys/aio.rs

@@ -1,3 +1,4 @@
+// vim: tw=80
 //! POSIX Asynchronous I/O
 //!
 //! The POSIX AIO interface is used for asynchronous I/O on files and disk-like
@@ -31,8 +32,8 @@ use std::fmt::Debug;
 use std::marker::PhantomData;
 use std::mem;
 use std::ptr::{null, null_mut};
-use std::thread;
 use sys::signal::*;
+use std::thread;
 use sys::time::TimeSpec;
 
 libc_enum! {
@@ -111,15 +112,15 @@ impl<'a> Debug for Buffer<'a> {
     // not today.
     // https://github.com/rust-lang/rust/issues/1563
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &Buffer::None => write!(fmt, "None"),
-            &Buffer::Phantom(p) => p.fmt(fmt),
-            &Buffer::BoxedSlice(ref bs) => {
+        match *self {
+            Buffer::None => write!(fmt, "None"),
+            Buffer::Phantom(p) => p.fmt(fmt),
+            Buffer::BoxedSlice(ref bs) => {
                 let borrowed : &Borrow<[u8]> = bs.borrow();
                 write!(fmt, "BoxedSlice({:?})",
                     borrowed as *const Borrow<[u8]>)
             },
-            &Buffer::BoxedMutSlice(ref bms) => {
+            Buffer::BoxedMutSlice(ref bms) => {
                 let borrowed : &BorrowMut<[u8]> = bms.borrow();
                 write!(fmt, "BoxedMutSlice({:?})",
                     borrowed as *const BorrowMut<[u8]>)
@@ -1059,7 +1060,11 @@ pub struct LioCb<'a> {
     /// It must live for as long as any of the operations are still being
     /// processesed, because the aio subsystem uses its address as a unique
     /// identifier.
-    list: Vec<*mut libc::aiocb>
+    list: Vec<*mut libc::aiocb>,
+
+    /// A partial set of results.  This field will get populated by
+    /// `listio_resubmit` when an `LioCb` is resubmitted after an error
+    results: Vec<Option<Result<isize>>>
 }
 
 #[cfg(not(any(target_os = "ios", target_os = "macos")))]
@@ -1068,7 +1073,8 @@ impl<'a> LioCb<'a> {
     pub fn with_capacity(capacity: usize) -> LioCb<'a> {
         LioCb {
             aiocbs: Vec::with_capacity(capacity),
-            list: Vec::with_capacity(capacity)
+            list: Vec::with_capacity(capacity),
+            results: Vec::with_capacity(capacity)
         }
     }
 
@@ -1109,7 +1115,7 @@ impl<'a> LioCb<'a> {
     ///     LioOpcode::LIO_WRITE));
     /// liocb.listio(LioMode::LIO_WAIT,
     ///              SigevNotify::SigevNone).unwrap();
-    /// assert_eq!(liocb.aiocbs[0].aio_return().unwrap() as usize, WBUF.len());
+    /// assert_eq!(liocb.aio_return(0).unwrap() as usize, WBUF.len());
     /// # }
     /// ```
     ///
@@ -1121,7 +1127,8 @@ impl<'a> LioCb<'a> {
         let sigev = SigEvent::new(sigev_notify);
         let sigevp = &mut sigev.sigevent() as *mut libc::sigevent;
         self.list.clear();
-        for a in self.aiocbs.iter_mut() {
+        for a in &mut self.aiocbs {
+        //for a in self.aiocbs.iter_mut() {
             self.list.push(a as *mut AioCb<'a>
                              as *mut libc::aiocb);
         }
@@ -1130,6 +1137,114 @@ impl<'a> LioCb<'a> {
             libc::lio_listio(mode as i32, p, self.list.len() as i32, sigevp)
         }).map(|_| ())
     }
+
+    /// Resubmits any incomplete operations with [`lio_listio`].
+    ///
+    /// Sometimes, due to system resource limitations, an `lio_listio` call will
+    /// return `EIO`, or `EAGAIN`.  Or, if a signal is received, it may return
+    /// `EINTR`.  In any of these cases, only a subset of its constituent
+    /// operations will actually have been initiated.  `listio_incomplete` will
+    /// resubmit any operations that are still uninitiated.
+    ///
+    /// After calling `listio_resubmit`, results should be collected by
+    /// [`LioCb::aio_return`].
+    ///
+    /// # Examples
+    /// ```no_run
+    /// # extern crate tempfile;
+    /// # extern crate nix;
+    /// # use nix::Error;
+    /// # use nix::errno::Errno;
+    /// # use nix::sys::aio::*;
+    /// # use nix::sys::signal::SigevNotify;
+    /// # use std::os::unix::io::AsRawFd;
+    /// # use std::{thread, time};
+    /// # use tempfile::tempfile;
+    /// # fn main() {
+    /// const WBUF: &[u8] = b"abcdef123456";
+    /// let mut f = tempfile().unwrap();
+    /// let mut liocb = LioCb::with_capacity(1);
+    /// liocb.aiocbs.push(AioCb::from_slice( f.as_raw_fd(),
+    ///     2,   //offset
+    ///     WBUF,
+    ///     0,   //priority
+    ///     SigevNotify::SigevNone,
+    ///     LioOpcode::LIO_WRITE));
+    /// let mut err = liocb.listio(LioMode::LIO_WAIT, SigevNotify::SigevNone);
+    /// while err == Err(Error::Sys(Errno::EIO)) ||
+    ///       err == Err(Error::Sys(Errno::EAGAIN)) {
+    ///     thread::sleep(time::Duration::from_millis(10));
+    ///     err = liocb.listio_resubmit(LioMode::LIO_WAIT, SigevNotify::SigevNone);
+    /// }
+    /// assert_eq!(liocb.aio_return(0).unwrap() as usize, WBUF.len());
+    /// # }
+    /// ```
+    ///
+    /// # References
+    ///
+    /// [`lio_listio`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/lio_listio.html)
+    ///
+    /// [`AioCb::aio_return`] (struct.AioCb.html#method.aio_return)
+    /// [`AioCb::error`] (struct.AioCb.html#method.error)
+    /// [`LioCb::aio_return`] #method.aio_return
+    // Note: the addresses of any EINPROGRESS or EOK aiocbs _must_ not be
+    // changed by this method, because the kernel relies on their addresses
+    // being stable.
+    // Note: aiocbs that are Ok(()) must be finalized by aio_return, or else the
+    // sigev_notify will immediately refire.
+    pub fn listio_resubmit(&mut self, mode:LioMode,
+                           sigev_notify: SigevNotify) -> Result<()> {
+        let sigev = SigEvent::new(sigev_notify);
+        let sigevp = &mut sigev.sigevent() as *mut libc::sigevent;
+        self.list.clear();
+
+        while self.results.len() < self.aiocbs.len() {
+            self.results.push(None);
+        }
+
+        for (i, a) in self.aiocbs.iter_mut().enumerate() {
+            if self.results[i].is_some() {
+                // Already collected final status for this operation
+                continue;
+            }
+            match a.error() {
+                Ok(()) => {
+                    // aiocb is complete; collect its status and don't resubmit
+                    self.results[i] = Some(a.aio_return());
+                },
+                Err(Error::Sys(Errno::EAGAIN)) => {
+                    self.list.push(a as *mut AioCb<'a> as *mut libc::aiocb);
+                },
+                Err(Error::Sys(Errno::EINPROGRESS)) => {
+                    // aiocb is was successfully queued; no need to do anything
+                    ()
+                },
+                Err(Error::Sys(Errno::EINVAL)) => panic!(
+                    "AioCb was never submitted, or already finalized"),
+                _ => unreachable!()
+            }
+        }
+        let p = self.list.as_ptr();
+        Errno::result(unsafe {
+            libc::lio_listio(mode as i32, p, self.list.len() as i32, sigevp)
+        }).map(|_| ())
+    }
+
+    /// Collect final status for an individual `AioCb` submitted as part of an
+    /// `LioCb`.
+    ///
+    /// This is just like [`AioCb::aio_return`], except it takes into account
+    /// operations that were restarted by [`LioCb::listio_resubmit`]
+    ///
+    /// [`AioCb::aio_return`] (struct.AioCb.html#method.aio_return)
+    /// [`LioCb::listio_resubmit`] #method.listio_resubmit
+    pub fn aio_return(&mut self, i: usize) -> Result<isize> {
+        if i >= self.results.len() || self.results[i].is_none() {
+            self.aiocbs[i].aio_return()
+        } else {
+            self.results[i].unwrap()
+        }
+    }
 }
 
 #[cfg(not(any(target_os = "ios", target_os = "macos")))]
@@ -1146,6 +1261,7 @@ impl<'a> From<Vec<AioCb<'a>>> for LioCb<'a> {
     fn from(src: Vec<AioCb<'a>>) -> LioCb<'a> {
         LioCb {
             list: Vec::with_capacity(src.capacity()),
+            results: Vec::with_capacity(src.capacity()),
             aiocbs: src,
         }
     }

test/sys/test_aio.rs

@@ -513,8 +513,8 @@ fn test_liocb_listio_wait() {
         let err = liocb.listio(LioMode::LIO_WAIT, SigevNotify::SigevNone);
         err.expect("lio_listio");
 
-        assert!(liocb.aiocbs[0].aio_return().unwrap() as usize == WBUF.len());
-        assert!(liocb.aiocbs[1].aio_return().unwrap() as usize == rlen);
+        assert!(liocb.aio_return(0).unwrap() as usize == WBUF.len());
+        assert!(liocb.aio_return(1).unwrap() as usize == rlen);
     }
     assert!(rbuf.deref().deref() == b"3456");