2 files changed, 73 insertions, 1 deletions

diff --git a/src/sys/uio.rs b/src/sys/uio.rs
index 9f65cf09..99075b79 100644
--- a/src/sys/uio.rs
+++ b/src/sys/uio.rs
@@ -9,7 +9,7 @@ use std::os::unix::io::RawFd;
 
 mod ffi {
     use super::IoVec;
-    use libc::{ssize_t, c_int};
+    use libc::{ssize_t, c_int, size_t, off_t, c_void};
     use std::os::unix::io::RawFd;
 
     extern {
@@ -20,6 +20,16 @@ mod ffi {
         // vectorized version of read
         // doc: http://man7.org/linux/man-pages/man2/readv.2.html
         pub fn readv(fd: RawFd, iov: *const IoVec<&mut [u8]>, iovcnt: c_int) -> ssize_t;
+
+        // write to a file at a specified offset
+        // doc: http://man7.org/linux/man-pages/man2/pwrite.2.html
+        pub fn pwrite(fd: RawFd, buf: *const c_void, nbyte: size_t,
+                      offset: off_t) -> ssize_t;
+
+        // read from a file at a specified offset
+        // doc: http://man7.org/linux/man-pages/man2/pread.2.html
+        pub fn pread(fd: RawFd, buf: *mut c_void, nbyte: size_t, offset: off_t)
+                     -> ssize_t;
     }
 }
 
@@ -42,6 +52,30 @@ pub fn readv(fd: RawFd, iov: &mut [IoVec<&mut [u8]>]) -> Result<usize> {
     return Ok(res as usize)
 }
 
+pub fn pwrite(fd: RawFd, buf: &[u8], offset: i64) -> Result<usize> {
+    let res = unsafe {
+        ffi::pwrite(fd, buf.as_ptr() as *const c_void, buf.len() as size_t,
+                    offset)
+    };
+    if res < 0 {
+        Err(Error::Sys(Errno::last()))
+    } else {
+        Ok(res as usize)
+    }
+}
+
+pub fn pread(fd: RawFd, buf: &mut [u8], offset: i64) -> Result<usize>{
+    let res = unsafe {
+        ffi::pread(fd, buf.as_mut_ptr() as *mut c_void, buf.len() as size_t,
+                   offset)
+    };
+    if res < 0 {
+        Err(Error::Sys(Errno::last()))
+    } else {
+        Ok(res as usize)
+    }
+}
+
 #[repr(C)]
 pub struct IoVec<T> {
     iov_base: *mut c_void,
diff --git a/test/sys/test_uio.rs b/test/sys/test_uio.rs
index 8f467001..0432b1e8 100644
--- a/test/sys/test_uio.rs
+++ b/test/sys/test_uio.rs
@@ -2,6 +2,8 @@ use nix::sys::uio::*;
 use nix::unistd::*;
 use rand::{thread_rng, Rng};
 use std::{cmp, iter};
+use std::fs::{OpenOptions, remove_file};
+use std::os::unix::io::AsRawFd;
 
 #[test]
 fn test_writev() {
@@ -90,3 +92,39 @@ fn test_readv() {
     let close_res = close(writer);
     assert!(close_res.is_ok());
 }
+
+#[test]
+fn test_pwrite() {
+    use std::io::Read;
+
+    let path = "pwrite_test_file";
+    let mut file = OpenOptions::new().write(true).read(true).create(true)
+                                    .truncate(true).open(path).unwrap();
+    let buf = [1u8;8];
+    assert_eq!(Ok(8), pwrite(file.as_raw_fd(), &buf, 8));
+    let mut file_content = Vec::new();
+    file.read_to_end(&mut file_content).unwrap();
+    let mut expected = vec![0u8;8];
+    expected.extend(vec![1;8]);
+    assert_eq!(file_content, expected);
+
+    remove_file(path).unwrap();
+}
+
+#[test]
+fn test_pread() {
+    use std::io::Write;
+
+    let path = "pread_test_file";
+    let mut file = OpenOptions::new().write(true).read(true).create(true)
+                                    .truncate(true).open(path).unwrap();
+    let file_content: Vec<u8> = (0..64).collect();
+    file.write_all(&file_content).unwrap();
+
+    let mut buf = [0u8;16];
+    assert_eq!(Ok(16), pread(file.as_raw_fd(), &mut buf, 16));
+    let expected: Vec<_> = (16..32).collect();
+    assert_eq!(&buf[..], &expected[..]);
+
+    remove_file(path).unwrap();
+}