Merge #1069

1069: Implement copy_file_range() r=asomers a=ArniDagur

This should fix the problems with #971 and #1008.

Co-authored-by: Árni Dagur <arnidg@protonmail.ch>

3 files changed, 107 insertions, 9 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 61c0cc80..16b7992d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#1079](https://github.com/nix-rust/nix/pull/1079))
 - Implemented `Clone`, `Copy`, `Debug`, `Eq`, `Hash`, and `PartialEq` for most
   types that support them. ([#1035](https://github.com/nix-rust/nix/pull/1035))
+- Added `copy_file_range` wrapper
+  ([#1069](https://github.com/nix-rust/nix/pull/1069))
 
 ### Changed
 - Support for `ifaddrs` now present when building for Android.
diff --git a/src/fcntl.rs b/src/fcntl.rs
index 6da62d87..3d932a53 100644
--- a/src/fcntl.rs
+++ b/src/fcntl.rs
@@ -8,6 +8,8 @@ use std::ffi::OsStr;
 use std::os::unix::ffi::OsStrExt;
 
 #[cfg(any(target_os = "android", target_os = "linux"))]
+use std::ptr; // For splice and copy_file_range
+#[cfg(any(target_os = "android", target_os = "linux"))]
 use sys::uio::IoVec;  // For vmsplice
 
 libc_bitflags!{
@@ -325,15 +327,70 @@ libc_bitflags! {
     }
 }
 
+/// Copy a range of data from one file to another
+///
+/// The `copy_file_range` system call performs an in-kernel copy between
+/// file descriptors `fd_in` and `fd_out` without the additional cost of
+/// transferring data from the kernel to user space and then back into the
+/// kernel. It copies up to `len` bytes of data from file descriptor `fd_in` to
+/// file descriptor `fd_out`, overwriting any data that exists within the
+/// requested range of the target file.
+///
+/// If the `off_in` and/or `off_out` arguments are used, the values
+/// will be mutated to reflect the new position within the file after
+/// copying. If they are not used, the relevant filedescriptors will be seeked
+/// to the new position.
+///
+/// On successful completion the number of bytes actually copied will be
+/// returned.
+#[cfg(any(target_os = "android", target_os = "linux"))]
+pub fn copy_file_range(
+    fd_in: RawFd,
+    off_in: Option<&mut libc::loff_t>,
+    fd_out: RawFd,
+    off_out: Option<&mut libc::loff_t>,
+    len: usize,
+) -> Result<usize> {
+    let off_in = off_in
+        .map(|offset| offset as *mut libc::loff_t)
+        .unwrap_or(ptr::null_mut());
+    let off_out = off_out
+        .map(|offset| offset as *mut libc::loff_t)
+        .unwrap_or(ptr::null_mut());
+
+    let ret = unsafe {
+        libc::syscall(
+            libc::SYS_copy_file_range,
+            fd_in,
+            off_in,
+            fd_out,
+            off_out,
+            len,
+            0,
+        )
+    };
+    Errno::result(ret).map(|r| r as usize)
+}
+
 #[cfg(any(target_os = "linux", target_os = "android"))]
-pub fn splice(fd_in: RawFd, off_in: Option<&mut libc::loff_t>,
-          fd_out: RawFd, off_out: Option<&mut libc::loff_t>,
-          len: usize, flags: SpliceFFlags) -> Result<usize> {
-    use std::ptr;
-    let off_in = off_in.map(|offset| offset as *mut _).unwrap_or(ptr::null_mut());
-    let off_out = off_out.map(|offset| offset as *mut _).unwrap_or(ptr::null_mut());
-
-    let ret = unsafe { libc::splice(fd_in, off_in, fd_out, off_out, len, flags.bits()) };
+pub fn splice(
+    fd_in: RawFd,
+    off_in: Option<&mut libc::loff_t>,
+    fd_out: RawFd,
+    off_out: Option<&mut libc::loff_t>,
+    len: usize,
+    flags: SpliceFFlags,
+) -> Result<usize> {
+    let off_in = off_in
+        .map(|offset| offset as *mut libc::loff_t)
+        .unwrap_or(ptr::null_mut());
+    let off_out = off_out
+        .map(|offset| offset as *mut libc::loff_t)
+        .unwrap_or(ptr::null_mut());
+
+    let ret = unsafe {
+        libc::splice(fd_in, off_in, fd_out, off_out, len, flags.bits())
+    };
     Errno::result(ret).map(|r| r as usize)
 }
 
diff --git a/test/test_fcntl.rs b/test/test_fcntl.rs
index bcc523bf..8d02f147 100644
--- a/test/test_fcntl.rs
+++ b/test/test_fcntl.rs
@@ -48,16 +48,55 @@ fn test_readlink() {
 #[cfg(any(target_os = "linux", target_os = "android"))]
 mod linux_android {
     use std::io::prelude::*;
+    use std::io::SeekFrom;
     use std::os::unix::prelude::*;
 
     use libc::loff_t;
 
-    use nix::fcntl::{SpliceFFlags, FallocateFlags, fallocate, splice, tee, vmsplice};
+    use nix::fcntl::*;
     use nix::sys::uio::IoVec;
     use nix::unistd::{close, pipe, read, write};
 
     use tempfile::{tempfile, NamedTempFile};
 
+    /// This test creates a temporary file containing the contents
+    /// 'foobarbaz' and uses the `copy_file_range` call to transfer
+    /// 3 bytes at offset 3 (`bar`) to another empty file at offset 0. The
+    /// resulting file is read and should contain the contents `bar`.
+    /// The from_offset should be updated by the call to reflect
+    /// the 3 bytes read (6).
+    ///
+    /// FIXME: This test is disabled for linux based builds, because Travis
+    /// Linux version is too old for `copy_file_range`.
+    #[test]
+    #[ignore]
+    fn test_copy_file_range() {
+        const CONTENTS: &[u8] = b"foobarbaz";
+
+        let mut tmp1 = tempfile().unwrap();
+        let mut tmp2 = tempfile().unwrap();
+
+        tmp1.write_all(CONTENTS).unwrap();
+        tmp1.flush().unwrap();
+
+        let mut from_offset: i64 = 3;
+        copy_file_range(
+            tmp1.as_raw_fd(),
+            Some(&mut from_offset),
+            tmp2.as_raw_fd(),
+            None,
+            3,
+        )
+        .unwrap();
+
+        let mut res: String = String::new();
+        tmp2.seek(SeekFrom::Start(0)).unwrap();
+        tmp2.read_to_string(&mut res).unwrap();
+
+        assert_eq!(res, String::from("bar"));
+        assert_eq!(from_offset, 6);
+    }
+
     #[test]
     fn test_splice() {
         const CONTENTS: &[u8] = b"abcdef123456";