Merge #872

872: Change sys::aio::lio_listio to sys::aio::LioCb::listio r=asomers a=asomers

The new LioCb structure allows us to control the exact arguments passed
to lio_listio, guaranteeing that each call gets a unique storage
location for the list argument.  This prevents clients from misusing
lio_listio in a way that causes events to get dropped from a kqueue

Fixes #870

1 files changed, 426 insertions, 187 deletions

diff --git a/src/sys/aio.rs b/src/sys/aio.rs
index fe8e9ed2..3d539821 100644
--- a/src/sys/aio.rs
+++ b/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
@@ -21,18 +22,18 @@
 //! not support this for all filesystems and devices.
 
 use {Error, Result};
-use bytes::{Bytes, BytesMut};
 use errno::Errno;
 use std::os::unix::io::RawFd;
 use libc::{c_void, off_t, size_t};
 use libc;
+use std::borrow::{Borrow, BorrowMut};
 use std::fmt;
 use std::fmt::Debug;
 use std::marker::PhantomData;
 use std::mem;
-use std::ops::Deref;
 use std::ptr::{null, null_mut};
 use sys::signal::*;
+use std::thread;
 use sys::time::TimeSpec;
 
 libc_enum! {
@@ -92,46 +93,38 @@ pub enum AioCancelStat {
 
 /// Owns (uniquely or shared) a memory buffer to keep it from `Drop`ing while
 /// the kernel has a pointer to it.
-#[derive(Clone, Debug)]
 pub enum Buffer<'a> {
     /// No buffer to own.
     ///
     /// Used for operations like `aio_fsync` that have no data, or for unsafe
     /// operations that work with raw pointers.
     None,
-    /// Immutable shared ownership `Bytes` object
-    // Must use out-of-line allocation so the address of the data will be
-    // stable.  `Bytes` and `BytesMut` sometimes dynamically allocate a buffer,
-    // and sometimes inline the data within the struct itself.
-    Bytes(Bytes),
-    /// Mutable uniquely owned `BytesMut` object
-    BytesMut(BytesMut),
     /// Keeps a reference to a slice
-    Phantom(PhantomData<&'a mut [u8]>)
+    Phantom(PhantomData<&'a mut [u8]>),
+    /// Generic thing that keeps a buffer from dropping
+    BoxedSlice(Box<Borrow<[u8]>>),
+    /// Generic thing that keeps a mutable buffer from dropping
+    BoxedMutSlice(Box<BorrowMut<[u8]>>),
 }
 
-impl<'a> Buffer<'a> {
-    /// Return the inner `Bytes`, if any
-    pub fn bytes(&self) -> Option<&Bytes> {
-        match *self {
-            Buffer::Bytes(ref x) => Some(x),
-            _ => None
-        }
-    }
-
-    /// Return the inner `BytesMut`, if any
-    pub fn bytes_mut(&self) -> Option<&BytesMut> {
-        match *self {
-            Buffer::BytesMut(ref x) => Some(x),
-            _ => None
-        }
-    }
-
-    /// Is this `Buffer` `None`?
-    pub fn is_none(&self) -> bool {
+impl<'a> Debug for Buffer<'a> {
+    // Note: someday it may be possible to Derive Debug for a trait object, but
+    // not today.
+    // https://github.com/rust-lang/rust/issues/1563
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            Buffer::None => true,
-            _ => false,
+            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) => {
+                let borrowed : &BorrowMut<[u8]> = bms.borrow();
+                write!(fmt, "BoxedMutSlice({:?})",
+                    borrowed as *const BorrowMut<[u8]>)
+            }
         }
     }
 }
@@ -149,7 +142,7 @@ pub struct AioCb<'a> {
     /// Optionally keeps a reference to the data.
     ///
     /// Used to keep buffers from `Drop`'ing, and may be returned once the
-    /// `AioCb` is completed by `into_buffer`.
+    /// `AioCb` is completed by [`buffer`](#method.buffer).
     buffer: Buffer<'a>
 }
 
@@ -165,6 +158,50 @@ impl<'a> AioCb<'a> {
         x
     }
 
+    /// Remove the inner boxed slice, if any, and return it.
+    ///
+    /// The returned value will be the argument that was passed to
+    /// `from_boxed_slice` when this `AioCb` was created.
+    ///
+    /// It is an error to call this method while the `AioCb` is still in
+    /// progress.
+    pub fn boxed_slice(&mut self) -> Option<Box<Borrow<[u8]>>> {
+        assert!(!self.in_progress, "Can't remove the buffer from an AioCb that's still in-progress.  Did you forget to call aio_return?");
+        if let Buffer::BoxedSlice(_) = self.buffer {
+            let mut oldbuffer = Buffer::None;
+            mem::swap(&mut self.buffer, &mut oldbuffer);
+            if let Buffer::BoxedSlice(inner) = oldbuffer {
+                Some(inner)
+            } else {
+                unreachable!();
+            }
+        } else {
+            None
+        }
+    }
+
+    /// Remove the inner boxed mutable slice, if any, and return it.
+    ///
+    /// The returned value will be the argument that was passed to
+    /// `from_boxed_mut_slice` when this `AioCb` was created.
+    ///
+    /// It is an error to call this method while the `AioCb` is still in
+    /// progress.
+    pub fn boxed_mut_slice(&mut self) -> Option<Box<BorrowMut<[u8]>>> {
+        assert!(!self.in_progress, "Can't remove the buffer from an AioCb that's still in-progress.  Did you forget to call aio_return?");
+        if let Buffer::BoxedMutSlice(_) = self.buffer {
+            let mut oldbuffer = Buffer::None;
+            mem::swap(&mut self.buffer, &mut oldbuffer);
+            if let Buffer::BoxedMutSlice(inner) = oldbuffer {
+                Some(inner)
+            } else {
+                unreachable!();
+            }
+        } else {
+            None
+        }
+    }
+
     /// Returns the underlying file descriptor associated with the `AioCb`
     pub fn fd(&self) -> RawFd {
         self.aiocb.aio_fildes
@@ -186,7 +223,7 @@ impl<'a> AioCb<'a> {
     /// # Examples
     ///
     /// Create an `AioCb` from a raw file descriptor and use it for an
-    /// [`fsync`](#method.from_bytes_mut) operation.
+    /// [`fsync`](#method.fsync) operation.
     ///
     /// ```
     /// # extern crate tempfile;
@@ -229,7 +266,7 @@ impl<'a> AioCb<'a> {
     /// operations, but only if the borrow checker can guarantee that the slice
     /// will outlive the `AioCb`.  That will usually be the case if the `AioCb`
     /// is stack-allocated.  If the borrow checker gives you trouble, try using
-    /// [`from_bytes_mut`](#method.from_bytes_mut) instead.
+    /// [`from_boxed_mut_slice`](#method.from_boxed_mut_slice) instead.
     ///
     /// # Parameters
     ///
@@ -299,17 +336,19 @@ impl<'a> AioCb<'a> {
         }
     }
 
-    /// Constructs a new `AioCb` from a `Bytes` object.
+    /// The safest and most flexible way to create an `AioCb`.
     ///
-    /// Unlike `from_slice`, this method returns a structure suitable for
+    /// Unlike [`from_slice`], this method returns a structure suitable for
     /// placement on the heap.  It may be used for write operations, but not
-    /// read operations.
+    /// read operations.  Unlike `from_ptr`, this method will ensure that the
+    /// buffer doesn't `drop` while the kernel is still processing it.  Any
+    /// object that can be borrowed as a boxed slice will work.
     ///
     /// # Parameters
     ///
     /// * `fd`:           File descriptor.  Required for all aio functions.
     /// * `offs`:         File offset
-    /// * `buf`:          A shared memory buffer
+    /// * `buf`:          A boxed slice-like object
     /// * `prio`:         If POSIX Prioritized IO is supported, then the
     ///                   operation will be prioritized at the process's
     ///                   priority level minus `prio`
@@ -321,15 +360,13 @@ impl<'a> AioCb<'a> {
     ///
     /// # Examples
     ///
-    /// Create an `AioCb` from a `Bytes` object and use it for writing.
+    /// Create an `AioCb` from a Vector and use it for writing
     ///
     /// ```
-    /// # extern crate bytes;
     /// # extern crate tempfile;
     /// # extern crate nix;
     /// # use nix::errno::Errno;
     /// # use nix::Error;
-    /// # use bytes::Bytes;
     /// # use nix::sys::aio::*;
     /// # use nix::sys::signal::SigevNotify;
     /// # use std::{thread, time};
@@ -337,11 +374,12 @@ impl<'a> AioCb<'a> {
     /// # use std::os::unix::io::AsRawFd;
     /// # use tempfile::tempfile;
     /// # fn main() {
-    /// let wbuf = Bytes::from(&b"CDEF"[..]);
+    /// let wbuf = Box::new(Vec::from("CDEF"));
+    /// let expected_len = wbuf.len();
     /// let mut f = tempfile().unwrap();
-    /// let mut aiocb = AioCb::from_bytes( f.as_raw_fd(),
+    /// let mut aiocb = AioCb::from_boxed_slice( f.as_raw_fd(),
     ///     2,   //offset
-    ///     wbuf.clone(),
+    ///     wbuf,
     ///     0,   //priority
     ///     SigevNotify::SigevNone,
     ///     LioOpcode::LIO_NOP);
@@ -349,72 +387,103 @@ impl<'a> AioCb<'a> {
     /// while (aiocb.error() == Err(Error::from(Errno::EINPROGRESS))) {
     ///     thread::sleep(time::Duration::from_millis(10));
     /// }
-    /// assert_eq!(aiocb.aio_return().unwrap() as usize, wbuf.len());
+    /// assert_eq!(aiocb.aio_return().unwrap() as usize, expected_len);
     /// # }
     /// ```
-    pub fn from_bytes(fd: RawFd, offs: off_t, buf: Bytes,
+    ///
+    /// Create an `AioCb` from a `Bytes` object
+    ///
+    /// ```
+    /// # extern crate bytes;
+    /// # extern crate tempfile;
+    /// # extern crate nix;
+    /// # use bytes::Bytes;
+    /// # use nix::sys::aio::*;
+    /// # use nix::sys::signal::SigevNotify;
+    /// # use std::os::unix::io::AsRawFd;
+    /// # use tempfile::tempfile;
+    /// # fn main() {
+    /// let wbuf = Box::new(Bytes::from(&b"CDEF"[..]));
+    /// let mut f = tempfile().unwrap();
+    /// let mut aiocb = AioCb::from_boxed_slice( f.as_raw_fd(),
+    ///     2,   //offset
+    ///     wbuf,
+    ///     0,   //priority
+    ///     SigevNotify::SigevNone,
+    ///     LioOpcode::LIO_NOP);
+    /// # }
+    /// ```
+    ///
+    /// If a library needs to work with buffers that aren't `Box`ed, it can
+    /// create a `Box`ed container for use with this method.  Here's an example
+    /// using an un`Box`ed `Bytes` object.
+    ///
+    /// ```
+    /// # extern crate bytes;
+    /// # extern crate tempfile;
+    /// # extern crate nix;
+    /// # use bytes::Bytes;
+    /// # use nix::sys::aio::*;
+    /// # use nix::sys::signal::SigevNotify;
+    /// # use std::borrow::Borrow;
+    /// # use std::os::unix::io::AsRawFd;
+    /// # use tempfile::tempfile;
+    /// struct BytesContainer(Bytes);
+    /// impl Borrow<[u8]> for BytesContainer {
+    ///     fn borrow(&self) -> &[u8] {
+    ///         self.0.as_ref()
+    ///     }
+    /// }
+    /// fn main() {
+    ///     let wbuf = Bytes::from(&b"CDEF"[..]);
+    ///     let boxed_wbuf = Box::new(BytesContainer(wbuf));
+    ///     let mut f = tempfile().unwrap();
+    ///     let mut aiocb = AioCb::from_boxed_slice( f.as_raw_fd(),
+    ///         2,   //offset
+    ///         boxed_wbuf,
+    ///         0,   //priority
+    ///         SigevNotify::SigevNone,
+    ///         LioOpcode::LIO_NOP);
+    /// }
+    /// ```
+    ///
+    /// [`from_slice`]: #method.from_slice
+    pub fn from_boxed_slice(fd: RawFd, offs: off_t, buf: Box<Borrow<[u8]>>,
                       prio: libc::c_int, sigev_notify: SigevNotify,
                       opcode: LioOpcode) -> AioCb<'a> {
-        // Small BytesMuts are stored inline.  Inline storage is a no-no,
-        // because we store a pointer to the buffer in the AioCb before
-        // returning the Buffer by move.  If the buffer is too small, reallocate
-        // it to force out-of-line storage
-        // TODO: Add an is_inline() method to BytesMut, and a way to explicitly
-        // force out-of-line allocation.
-        let buf2 = if buf.len() < 64 {
-            // Reallocate to force out-of-line allocation
-            let mut ool = Bytes::with_capacity(64);
-            ool.extend_from_slice(buf.deref());
-            ool
-        } else {
-            buf
-        };
         let mut a = AioCb::common_init(fd, prio, sigev_notify);
+        {
+            let borrowed : &Borrow<[u8]> = buf.borrow();
+            let slice : &[u8] = borrowed.borrow();
+            a.aio_nbytes = slice.len() as size_t;
+            a.aio_buf = slice.as_ptr() as *mut c_void;
+        }
         a.aio_offset = offs;
-        a.aio_nbytes = buf2.len() as size_t;
-        a.aio_buf = buf2.as_ptr() as *mut c_void;
         a.aio_lio_opcode = opcode as libc::c_int;
 
         AioCb {
             aiocb: a,
             mutable: false,
             in_progress: false,
-            buffer: Buffer::Bytes(buf2),
+            buffer: Buffer::BoxedSlice(buf),
         }
     }
 
-    /// Constructs a new `AioCb` from a `BytesMut` object.
+    /// The safest and most flexible way to create an `AioCb` for reading.
     ///
-    /// Unlike `from_mut_slice`, this method returns a structure suitable for
-    /// placement on the heap.  It may be used for both reads and writes.
-    ///
-    /// # Parameters
-    ///
-    /// * `fd`:           File descriptor.  Required for all aio functions.
-    /// * `offs`:         File offset
-    /// * `buf`:          An owned memory buffer
-    /// * `prio`:         If POSIX Prioritized IO is supported, then the
-    ///                   operation will be prioritized at the process's
-    ///                   priority level minus `prio`
-    /// * `sigev_notify`: Determines how you will be notified of event
-    ///                   completion.
-    /// * `opcode`:       This field is only used for `lio_listio`.  It
-    ///                   determines which operation to use for this individual
-    ///                   aiocb
+    /// Like [`from_boxed_slice`], but the slice is a mutable one.  More
+    /// flexible than [`from_mut_slice`], because a wide range of objects can be
+    /// used.
     ///
     /// # Examples
     ///
-    /// Create an `AioCb` from a `BytesMut` and use it for reading.  In this
-    /// example the `AioCb` is stack-allocated, so we could've used
-    /// `from_mut_slice` instead.
+    /// Create an `AioCb` from a Vector and use it for reading
     ///
     /// ```
-    /// # extern crate bytes;
     /// # extern crate tempfile;
     /// # extern crate nix;
     /// # use nix::errno::Errno;
     /// # use nix::Error;
-    /// # use bytes::BytesMut;
     /// # use nix::sys::aio::*;
     /// # use nix::sys::signal::SigevNotify;
     /// # use std::{thread, time};
@@ -424,10 +493,10 @@ impl<'a> AioCb<'a> {
     /// # fn main() {
     /// const INITIAL: &[u8] = b"abcdef123456";
     /// const LEN: usize = 4;
-    /// let rbuf = BytesMut::from(vec![0; LEN]);
+    /// let rbuf = Box::new(vec![0; LEN]);
     /// let mut f = tempfile().unwrap();
     /// f.write_all(INITIAL).unwrap();
-    /// let mut aiocb = AioCb::from_bytes_mut( f.as_raw_fd(),
+    /// let mut aiocb = AioCb::from_boxed_mut_slice( f.as_raw_fd(),
     ///     2,   //offset
     ///     rbuf,
     ///     0,   //priority
@@ -438,33 +507,33 @@ impl<'a> AioCb<'a> {
     ///     thread::sleep(time::Duration::from_millis(10));
     /// }
     /// assert_eq!(aiocb.aio_return().unwrap() as usize, LEN);
-    /// let buffer = aiocb.into_buffer();
+    /// let mut buffer = aiocb.boxed_mut_slice().unwrap();
     /// const EXPECT: &[u8] = b"cdef";
-    /// assert_eq!(buffer.bytes_mut().unwrap(), EXPECT);
+    /// assert_eq!(buffer.borrow_mut(), EXPECT);
     /// # }
     /// ```
-    pub fn from_bytes_mut(fd: RawFd, offs: off_t, buf: BytesMut,
-                          prio: libc::c_int, sigev_notify: SigevNotify,
-                          opcode: LioOpcode) -> AioCb<'a> {
-        let mut buf2 = if buf.len() < 64 {
-            // Reallocate to force out-of-line allocation
-            let mut ool = BytesMut::with_capacity(64);
-            ool.extend_from_slice(buf.deref());
-            ool
-        } else {
-            buf
-        };
+    ///
+    /// [`from_boxed_slice`]: #method.from_boxed_slice
+    /// [`from_mut_slice`]: #method.from_mut_slice
+    pub fn from_boxed_mut_slice(fd: RawFd, offs: off_t,
+                                mut buf: Box<BorrowMut<[u8]>>,
+                                prio: libc::c_int, sigev_notify: SigevNotify,
+                                opcode: LioOpcode) -> AioCb<'a> {
         let mut a = AioCb::common_init(fd, prio, sigev_notify);
+        {
+            let borrowed : &mut BorrowMut<[u8]> = buf.borrow_mut();
+            let slice : &mut [u8] = borrowed.borrow_mut();
+            a.aio_nbytes = slice.len() as size_t;
+            a.aio_buf = slice.as_mut_ptr() as *mut c_void;
+        }
         a.aio_offset = offs;
-        a.aio_nbytes = buf2.len() as size_t;
-        a.aio_buf = buf2.as_mut_ptr() as *mut c_void;
         a.aio_lio_opcode = opcode as libc::c_int;
 
         AioCb {
             aiocb: a,
             mutable: true,
             in_progress: false,
-            buffer: Buffer::BytesMut(buf2),
+            buffer: Buffer::BoxedMutSlice(buf),
         }
     }
 
@@ -474,7 +543,7 @@ impl<'a> AioCb<'a> {
     /// placement on the heap.  It may be used for both reads and writes.  Due
     /// to its unsafety, this method is not recommended.  It is most useful when
     /// heap allocation is required but for some reason the data cannot be
-    /// converted to a `BytesMut`.
+    /// wrapped in a `struct` that implements `BorrowMut<[u8]>`
     ///
     /// # Parameters
     ///
@@ -518,7 +587,8 @@ impl<'a> AioCb<'a> {
     /// Unlike `from_slice`, this method returns a structure suitable for
     /// placement on the heap.  Due to its unsafety, this method is not
     /// recommended.  It is most useful when heap allocation is required but for
-    /// some reason the data cannot be converted to a `Bytes`.
+    /// some reason the data cannot be wrapped in a `struct` that implements
+    /// `Borrow<[u8]>`
     ///
     /// # Parameters
     ///
@@ -623,19 +693,6 @@ impl<'a> AioCb<'a> {
         }
     }
 
-    /// Consumes the `aiocb` and returns its inner `Buffer`, if any.
-    ///
-    /// This method is especially useful when reading into a `BytesMut`, because
-    /// that type does not support shared ownership.
-    pub fn into_buffer(mut self) -> Buffer<'static> {
-        let buf = self.buffer();
-        match buf {
-            Buffer::BytesMut(x) => Buffer::BytesMut(x),
-            Buffer::Bytes(x) => Buffer::Bytes(x),
-            _ => Buffer::None
-        }
-    }
-
     fn common_init(fd: RawFd, prio: libc::c_int,
                    sigev_notify: SigevNotify) -> libc::aiocb {
         // Use mem::zeroed instead of explicitly zeroing each field, because the
@@ -669,12 +726,10 @@ impl<'a> AioCb<'a> {
     /// result.
     ///
     /// ```
-    /// # extern crate bytes;
     /// # extern crate tempfile;
     /// # extern crate nix;
     /// # use nix::errno::Errno;
     /// # use nix::Error;
-    /// # use bytes::Bytes;
     /// # use nix::sys::aio::*;
     /// # use nix::sys::signal::SigevNotify;
     /// # use std::{thread, time};
@@ -682,11 +737,11 @@ impl<'a> AioCb<'a> {
     /// # use std::os::unix::io::AsRawFd;
     /// # use tempfile::tempfile;
     /// # fn main() {
-    /// let wbuf = Bytes::from(&b"CDEF"[..]);
+    /// let wbuf = b"CDEF";
     /// let mut f = tempfile().unwrap();
-    /// let mut aiocb = AioCb::from_bytes( f.as_raw_fd(),
+    /// let mut aiocb = AioCb::from_slice( f.as_raw_fd(),
     ///     2,   //offset
-    ///     wbuf.clone(),
+    ///     &wbuf[..],
     ///     0,   //priority
     ///     SigevNotify::SigevNone,
     ///     LioOpcode::LIO_NOP);
@@ -870,12 +925,10 @@ impl<'a> AioCb<'a> {
 /// descriptor.
 ///
 /// ```
-/// # extern crate bytes;
 /// # extern crate tempfile;
 /// # extern crate nix;
 /// # use nix::errno::Errno;
 /// # use nix::Error;
-/// # use bytes::Bytes;
 /// # use nix::sys::aio::*;
 /// # use nix::sys::signal::SigevNotify;
 /// # use std::{thread, time};
@@ -883,11 +936,11 @@ impl<'a> AioCb<'a> {
 /// # use std::os::unix::io::AsRawFd;
 /// # use tempfile::tempfile;
 /// # fn main() {
-/// let wbuf = Bytes::from(&b"CDEF"[..]);
+/// let wbuf = b"CDEF";
 /// let mut f = tempfile().unwrap();
-/// let mut aiocb = AioCb::from_bytes( f.as_raw_fd(),
+/// let mut aiocb = AioCb::from_slice( f.as_raw_fd(),
 ///     2,   //offset
-///     wbuf.clone(),
+///     &wbuf[..],
 ///     0,   //priority
 ///     SigevNotify::SigevNone,
 ///     LioOpcode::LIO_NOP);
@@ -965,63 +1018,6 @@ pub fn aio_suspend(list: &[&AioCb], timeout: Option<TimeSpec>) -> Result<()> {
     }).map(drop)
 }
 
-
-/// Submits multiple asynchronous I/O requests with a single system call.
-///
-/// They are not guaranteed to complete atomically, and the order in which the
-/// requests are carried out is not specified.  Reads, writes, and fsyncs may be
-/// freely mixed.
-///
-/// This function is useful for reducing the context-switch overhead of
-/// submitting many AIO operations.  It can also be used with
-/// `LioMode::LIO_WAIT` to block on the result of several independent
-/// operations.  Used that way, it is often useful in programs that otherwise
-/// make little use of AIO.
-///
-/// # Examples
-///
-/// Use `lio_listio` to submit an aio operation and wait for its completion.  In
-/// this case, there is no need to use `aio_suspend` to wait or `AioCb#error` to
-/// poll.
-///
-/// ```
-/// # extern crate tempfile;
-/// # extern crate nix;
-/// # use nix::sys::aio::*;
-/// # use nix::sys::signal::SigevNotify;
-/// # use std::os::unix::io::AsRawFd;
-/// # use tempfile::tempfile;
-/// # fn main() {
-/// const WBUF: &[u8] = b"abcdef123456";
-/// let mut f = tempfile().unwrap();
-/// let mut aiocb = AioCb::from_slice( f.as_raw_fd(),
-///     2,   //offset
-///     WBUF,
-///     0,   //priority
-///     SigevNotify::SigevNone,
-///     LioOpcode::LIO_WRITE);
-/// lio_listio(LioMode::LIO_WAIT,
-///            &[&mut aiocb],
-///            SigevNotify::SigevNone).unwrap();
-/// assert_eq!(aiocb.aio_return().unwrap() as usize, WBUF.len());
-/// # }
-/// ```
-///
-/// # References
-///
-/// [`lio_listio`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/lio_listio.html)
-#[cfg(not(any(target_os = "ios", target_os = "macos")))]
-pub fn lio_listio(mode: LioMode, list: &[&mut AioCb],
-                  sigev_notify: SigevNotify) -> Result<()> {
-    let sigev = SigEvent::new(sigev_notify);
-    let sigevp = &mut sigev.sigevent() as *mut libc::sigevent;
-    let plist = list as *const [&mut AioCb] as *const [*mut libc::aiocb];
-    let p = plist as *const *mut libc::aiocb;
-    Errno::result(unsafe {
-        libc::lio_listio(mode as i32, p, list.len() as i32, sigevp)
-    }).map(drop)
-}
-
 impl<'a> Debug for AioCb<'a> {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         fmt.debug_struct("AioCb")
@@ -1042,6 +1038,249 @@ impl<'a> Drop for AioCb<'a> {
     /// If the `AioCb` has no remaining state in the kernel, just drop it.
     /// Otherwise, dropping constitutes a resource leak, which is an error
     fn drop(&mut self) {
-        assert!(!self.in_progress, "Dropped an in-progress AioCb");
+        assert!(thread::panicking() || !self.in_progress,
+                "Dropped an in-progress AioCb");
+    }
+}
+
+/// LIO Control Block.
+///
+/// The basic structure used to issue multiple AIO operations simultaneously.
+#[cfg(not(any(target_os = "ios", target_os = "macos")))]
+pub struct LioCb<'a> {
+    /// A collection of [`AioCb`]s.  All of these will be issued simultaneously
+    /// by the [`listio`] method.
+    ///
+    /// [`AioCb`]: struct.AioCb.html
+    /// [`listio`]: #method.listio
+    pub aiocbs: Vec<AioCb<'a>>,
+
+    /// The actual list passed to `libc::lio_listio`.
+    ///
+    /// 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>,
+
+    /// 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")))]
+impl<'a> LioCb<'a> {
+    /// Initialize an empty `LioCb`
+    pub fn with_capacity(capacity: usize) -> LioCb<'a> {
+        LioCb {
+            aiocbs: Vec::with_capacity(capacity),
+            list: Vec::with_capacity(capacity),
+            results: Vec::with_capacity(capacity)
+        }
+    }
+
+    /// Submits multiple asynchronous I/O requests with a single system call.
+    ///
+    /// They are not guaranteed to complete atomically, and the order in which
+    /// the requests are carried out is not specified.  Reads, writes, and
+    /// fsyncs may be freely mixed.
+    ///
+    /// This function is useful for reducing the context-switch overhead of
+    /// submitting many AIO operations.  It can also be used with
+    /// `LioMode::LIO_WAIT` to block on the result of several independent
+    /// operations.  Used that way, it is often useful in programs that
+    /// otherwise make little use of AIO.
+    ///
+    /// # Examples
+    ///
+    /// Use `listio` to submit an aio operation and wait for its completion.  In
+    /// this case, there is no need to use [`aio_suspend`] to wait or
+    /// [`AioCb::error`] to poll.
+    ///
+    /// ```
+    /// # extern crate tempfile;
+    /// # extern crate nix;
+    /// # use nix::sys::aio::*;
+    /// # use nix::sys::signal::SigevNotify;
+    /// # use std::os::unix::io::AsRawFd;
+    /// # 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));
+    /// liocb.listio(LioMode::LIO_WAIT,
+    ///              SigevNotify::SigevNone).unwrap();
+    /// assert_eq!(liocb.aio_return(0).unwrap() as usize, WBUF.len());
+    /// # }
+    /// ```
+    ///
+    /// # References
+    ///
+    /// [`lio_listio`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/lio_listio.html)
+    ///
+    /// [`aio_suspend`]: fn.aio_suspend.html
+    /// [`AioCb::error`]: struct.AioCb.html#method.error
+    pub fn listio(&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();
+        for a in &mut self.aiocbs {
+            a.in_progress = true;
+            self.list.push(a as *mut AioCb<'a>
+                             as *mut libc::aiocb);
+        }
+        let p = self.list.as_ptr();
+        Errno::result(unsafe {
+            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_resubmit` 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)
+    ///
+    /// [`lio_listio`]: http://pubs.opengroup.org/onlinepubs/9699919799/functions/lio_listio.html
+    /// [`LioCb::aio_return`]: struct.LioCb.html#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()
+        }
+    }
+
+    /// Retrieve error status of an individual `AioCb` submitted as part of an
+    /// `LioCb`.
+    ///
+    /// This is just like [`AioCb::error`], except it takes into account
+    /// operations that were restarted by [`LioCb::listio_resubmit`]
+    ///
+    /// [`AioCb::error`]: struct.AioCb.html#method.error
+    /// [`LioCb::listio_resubmit`]: #method.listio_resubmit
+    pub fn error(&mut self, i: usize) -> Result<()> {
+        if i >= self.results.len() || self.results[i].is_none() {
+            self.aiocbs[i].error()
+        } else {
+            Ok(())
+        }
+    }
+}
+
+#[cfg(not(any(target_os = "ios", target_os = "macos")))]
+impl<'a> Debug for LioCb<'a> {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        fmt.debug_struct("LioCb")
+            .field("aiocbs", &self.aiocbs)
+            .finish()
+    }
+}
+
+#[cfg(not(any(target_os = "ios", target_os = "macos")))]
+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,
+        }
     }
 }