Added basic (tx, rx) fd-overlap mapping with `MappedFile::try_new_buffer()`.

Fortune for mapped-file's current commit: Small blessing − 小吉

src/lib.rs

@@ -121,37 +121,53 @@ impl<T: AsRawFd> MappedFile<T> {
 
     /// Returns a dual mapping `(tx, rx)`, into the same file.
     ///
+    /// This essentially creates s "sender" `tx`, and "receiver" `rx` mapping over the same data.
+    /// The sender is *write only*, and the receiver is *read only*.
+    ///
+    /// # Sharing modes
+    /// `B` is used for the counter over the file handle `T`. Currently it can be
+    /// * `buffer::Shared` - A `Send`able mapping, use this for concurrent processing.
+    /// * `buffer::Private` - A `!Send` mapping, use this for when both returned maps are only used on the same thread that this function was called from.
+    ///
     /// # Note
     /// `len` **must** be a multiple of the used page size (or hugepage size, if `flags` is set to use one) for this to work.
-    pub fn try_new_buffer<B: buffer::TwoBufferProvider<T>>(file: T, len: usize, rings: impl Into<Option<std::num::NonZeroUsize>>, allow_unsafe_writes: bool, flags: impl flags::MapFlags) -> Result<(MappedFile<B>, MappedFile<B>), TryNewError<T>>
+    pub fn try_new_buffer<B: buffer::TwoBufferProvider<T>>(file: T, len: usize, flags: impl flags::MapFlags) -> Result<(MappedFile<B>, MappedFile<B>), TryNewError<T>>
+    {
+	Self::try_new_buffer_raw::<B>(file, len, None, false, flags)
+    }
+    #[inline] 
+    pub(crate) fn try_new_buffer_raw<B: buffer::TwoBufferProvider<T>>(file: T, len: usize, rings: impl Into<Option<std::num::NonZeroUsize>>, allow_unsafe_writes: bool, flags: impl flags::MapFlags) -> Result<(MappedFile<B>, MappedFile<B>), TryNewError<T>>
     {
 	const NULL: *mut libc::c_void = ptr::null_mut();
-	use std::{
-	    //rc::Rc,
-	    cell::RefCell,
-	};
 
-	let mut defer_set = {
+	macro_rules! try_map_or {
-	    let mut defer_set: Vec<(*mut u8, usize)> = Vec::new();
-	    defer!(ref defer_set => |set: Vec<(*mut u8, usize)>| {
-		for (ptr, len) in set {
-		    unsafe {
-			libc::munmap(ptr as *mut _, len);
-		    }
-		}
-	    });
-	    defer_set
-	};
-	
-	macro_rules! try_map {
 	    ($($tt:tt)*) => {
 		match unsafe {
 		    mmap($($tt)*)
+		} {
+		    MAP_FAILED => Err(io::Error::last_os_error()),
+		    NULL => _panic_invalid_address(),
+		    ptr => Ok(unsafe {
+			
+			UniqueSlice {
+			    mem: NonNull::new_unchecked(ptr as *mut u8),
+			    end: match NonNull::new((ptr as *mut u8).add(len)) {
+				Some(n) => n,
+				_ => _panic_invalid_address(),
+			    }
+			}
+		    })
+		}.map(MappedSlice)
+	    };
+	}
+	macro_rules! try_map {
+	    ($($tt:tt)*) => {
+		MappedSlice(match unsafe {
+		    mmap($($tt)*)
 		} {
 		    MAP_FAILED => return Err(TryNewError::wrap_last_error(file)),
 		    NULL => _panic_invalid_address(),
 		    ptr => unsafe {
-			defer_set.push((ptr as *mut u8, len));
 			
 			UniqueSlice {
 			    mem: NonNull::new_unchecked(ptr as *mut u8),
@@ -161,34 +177,75 @@ impl<T: AsRawFd> MappedFile<T> {
 			    }
 			}
 		    }
+		})
+	    };
+	}
+
+	macro_rules! unwrap {
+	    ($err:expr) => {
+		match $err {
+		    Ok(v) => v,
+		    Err(e) => return Err(TryNewError::wrap((e, file))),
 		}
 	    };
 	}
-	let (prot_r, prot_w) = if allow_unsafe_writes {
+	
+	let (prot_w, prot_r) = if allow_unsafe_writes {
 	    let p = Perm::ReadWrite.get_prot();
 	    (p, p)
 	} else {
 	    (Perm::Writeonly.get_prot(), Perm::Readonly.get_prot())
 	};
-	match rings.into() {
+	// Move into dual buffer
+
+	let (tx, rx) = match rings.into() {
 	    None => {
 		// No rings, just create two mappings at same addr.
 		let flags = flags.get_mmap_flags();
-		let tm = try_map!(NULL, len, prot_w, flags, file.as_raw_fd(), 0); 
+		let mut root = try_map!(NULL, len * 2, libc::PROT_NONE, (flags & !libc::MAP_SHARED) | libc::MAP_PRIVATE | libc::MAP_ANONYMOUS, -1, 0);
-		let wm = try_map!(tm.mem.as_ptr() as *mut _, len, prot_r, flags | libc::MAP_FIXED, file.as_raw_fd(), 0);
+		let rawfd = file.as_raw_fd();
-		//TODO... How to create the first `A?rc` over `file`?
+		
+		let rm = try_map!(root.0.as_mut_ptr().add(len) as *mut _, len, prot_r, flags | libc::MAP_FIXED, rawfd, 0); // Map reader at offset `len` from `root`.
+		let tm = try_map!(root.0.as_mut_ptr() as *mut _, len, prot_w, flags | libc::MAP_FIXED, rawfd, 0);  // Map writer at `root`, unmapping the anonymous map used to reserve the pages.
+
+		let tf = B::from_value(file);
+		let rf = B::from_wrapper(tf.as_wrapper());
+		(MappedFile {
+		    file: tf,
+		    map: tm
+		}, MappedFile {
+		    file: rf,
+		    map: rm,
+		})
 	    },
 	    Some(pages) => {
-		// Create anon mapping
+		// Create anon mapping at full length
-		try_map!(NULL, len, libc::PROT_NONE, flags.get_mmap_flags() | libc::MAP_ANONYMOUS, file.as_raw_fd(), 0);
+		let full_len = unwrap!((len * 2)
+				       .checked_mul(pages.get())
+				       .ok_or_else(|| io::Error::new(io::ErrorKind::OutOfMemory,
+								     format!("Could not map {} pages of size {len}. Value would overflow", pages.get()))));
+		let flags = flags.get_mmap_flags();
+		let mut root = try_map!(NULL, full_len, libc::PROT_NONE, libc::MAP_PRIVATE | libc::MAP_ANONYMOUS, -1, 0);
+		let pivots = {
+		    let rawfd = file.as_raw_fd();
+		    let pivots: io::Result<Vec<_>> = std::iter::successors(unsafe { Some(root.0.as_mut_ptr().add(full_len)) }, |&x| unsafe { Some(x.sub(len * 2)) }) // Map in reverse, from end of `root`, and overwrite the `root` mapping last.
+			.take(pages.get())
+			.map(|base| {
+			    let tm = try_map_or!(base as *mut _, len, prot_w, flags | libc::MAP_FIXED, rawfd, 0)?;
+			    let rm = try_map_or!(base.add(len) as *mut _, len, prot_r, flags | libc::MAP_FIXED,rawfd, 0 )?;
+
+			    Ok((tm, rm))
+			})
+			.collect();
+		    unwrap!(pivots)
+		};
+		
+		    todo!("We can't carry `pivots` over to return from this function; the data is needed for unmapping the ring...");
+		todo!("The mapping we'd be using is `root`. But we need to unmap `pivots` in reverse order when the returned `MappedFile` is dropped...")
 	    }
-	    
+	};
-	}
+	Ok((tx, rx))
-
+    }    
-	// Must happen at the end, so that maps dont get defer free'd
-	defer_set.clear();
-    }
-    
     /// Map the file `file` to `len` bytes with memory protection as provided by `perm`, and
     /// mapping flags provided by `flags`.
     ///
@@ -449,6 +506,15 @@ impl<T> TryNewError<T>
 	    value,
 	}
     }
+
+    #[inline] 
+    fn wrap((error, value): (impl Into<io::Error>, T)) -> Self
+    {
+	Self {
+	    error: Box::new(error.into()),
+	    value
+	}
+    }
     /// Consume into the contained value 
     #[inline] 
     pub fn into_inner(self) -> T

src/ring/buffer.rs

@@ -14,6 +14,13 @@ pub trait TwoBufferProvider<T: ?Sized>
     type ControlWrapper: Borrow<T>;
 
     fn as_wrapper(&self) -> &Self::ControlWrapper;
+    fn from_wrapper_boxed(r: &Self::ControlWrapper) -> Box<Self>;
+
+    #[inline(always)] 
+    fn from_wrapper(r: &Self::ControlWrapper) -> Self
+    where Self: Sized {
+	*Self::from_wrapper_boxed(r)
+    }
 
     #[inline(always)] 
     fn inner(&self) -> &T
@@ -22,15 +29,22 @@ pub trait TwoBufferProvider<T: ?Sized>
     }
 
     fn from_boxed(value: Box<T>) -> Box<Self>;
-//TODO: How do we give enough info to caller to create this?	
+
+    #[inline(always)] 
+    fn from_value(value: T) -> Self
+    where T: Sized,
+	  Self: Sized
+    {
+	*Self::from_boxed(Box::new(value))
+    }
 }
 
 /// For thread-sharable buffer holds
-#[derive(Debug, Clone)]
+#[derive(Debug)]
 pub struct Shared<T: ?Sized>(sync::Arc<T>);
 
 /// For non thread-sharable buffer holds
-#[derive(Debug, Clone)]
+#[derive(Debug)]
 pub struct Private<T: ?Sized>(rc::Rc<T>);
 
 impl<T: ?Sized> TwoBufferProvider<T> for Shared<T> {
@@ -43,7 +57,24 @@ impl<T: ?Sized> TwoBufferProvider<T> for Shared<T> {
 
     #[inline] 
     fn from_boxed(value: Box<T>) ->Box<Self> {
-	Box::new(Self(value.into()))
+	Box::new(Self(From::from(value)))
+    }
+
+    #[inline(always)]
+    fn from_value(value: T) -> Self
+    where T: Sized,
+	  Self: Sized {
+	Self(sync::Arc::new(value))
+    }
+
+    #[inline] 
+    fn from_wrapper_boxed(r: &Self::ControlWrapper) -> Box<Self> {
+	Box::new(Self(r.clone()))
+    }
+    #[inline(always)] 
+    fn from_wrapper(r: &Self::ControlWrapper) -> Self
+    where Self: Sized {
+	Self(r.clone())
     }
 }
 
@@ -65,7 +96,24 @@ impl<T: ?Sized> TwoBufferProvider<T> for Private<T> {
     
     #[inline] 
     fn from_boxed(value: Box<T>) ->Box<Self> {
-	Box::new(Self(value.into()))
+	Box::new(Self(From::from(value)))
+    }
+    
+    #[inline(always)]
+    fn from_value(value: T) -> Self
+    where T: Sized,
+	  Self: Sized {
+	Self(rc::Rc::new(value))
+    }
+    
+    #[inline] 
+    fn from_wrapper_boxed(r: &Self::ControlWrapper) -> Box<Self> {
+	Box::new(Self(r.clone()))
+    }
+    #[inline(always)] 
+    fn from_wrapper(r: &Self::ControlWrapper) -> Self
+    where Self: Sized {
+	Self(r.clone())
     }
 }
 
@@ -76,3 +124,50 @@ impl<T: ?Sized + AsRawFd> AsRawFd for Private<T>
 	self.as_wrapper().as_raw_fd()
     }
 }
+
+impl<T: ?Sized> Shared<T>
+{
+    /// Check if the connected mapping has not been dropped.
+    #[inline] 
+    pub fn is_connected(&self) -> bool
+    {
+	sync::Arc::strong_count(&self.0) > 1
+    }
+
+    /// Consume into an `Arc` instance over the file handle.
+    #[inline] 
+    pub fn into_arc(self) -> sync::Arc<T>
+    {
+	self.0
+    }
+
+    /// Get a reference of the file handle.
+    #[inline] 
+    pub fn inner(&self) -> &T
+    {
+	&self.0
+    }
+}
+impl<T: ?Sized> Private<T>
+{
+    /// Check if the connected mapping has not been dropped.
+    #[inline] 
+    pub fn is_connected(&self) -> bool
+    {
+	rc::Rc::strong_count(&self.0) > 1
+    }
+
+    /// Consume into an `Rc` instance over the file handle.
+    #[inline] 
+    pub fn into_rc(self) -> rc::Rc<T>
+    {
+	self.0
+    }
+
+    /// Get a reference of the file handle.
+    #[inline] 
+    pub fn inner(&self) -> &T
+    {
+	&self.0
+    }
+}