Merge #1105

1105: posix_fallocate support r=asomers a=dingxiangfei2009

This PR add [`posix_fallocate`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/posix_fallocate.html), which is available on
- Linux
- FreeBSD
- Android
- Emscripten
- Fuchsia
- WASI

Here is a question: for some reason, `posix_fallocate` returns `EBADF` instead of `EPIPE` if a FIFO file descriptor is passed in on Linux 4.19.64. In the test `EBADF` is used for now, but I would like to know if such behaviour is expected.

Co-authored-by: Ding Xiang Fei <dingxiangfei2009@gmail.com>

CHANGELOG.md

@@ -6,6 +6,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ## [Unreleased] - ReleaseDate
 ### Added
 
+- Added `posix_fallocate`.
+  ([#1105](https://github.com/nix-rust/nix/pull/1105))
+
 - Implemented `Default` for `FdSet`
   ([#1107](https://github.com/nix-rust/nix/pull/1107))
 

src/fcntl.rs

@@ -505,3 +505,24 @@ mod posix_fadvise {
         Errno::result(res)
     }
 }
+
+#[cfg(any(
+    target_os = "linux",
+    target_os = "android",
+    target_os = "emscripten",
+    target_os = "fuchsia",
+    any(target_os = "wasi", target_env = "wasi"),
+    target_os = "freebsd"
+))]
+pub fn posix_fallocate(
+    fd: RawFd,
+    offset: libc::off_t,
+    len: libc::off_t
+) -> Result<()> {
+    let res = unsafe { libc::posix_fallocate(fd, offset, len) };
+    match Errno::result(res) {
+        Err(err) => Err(err),
+        Ok(0) => Ok(()),
+        Ok(errno) => Err(crate::Error::Sys(Errno::from_i32(errno))),
+    }
+}

test/test_fcntl.rs

@@ -231,3 +231,60 @@ mod test_posix_fadvise {
         assert_eq!(errno, Errno::ESPIPE as i32);
     }
 }
+
+#[cfg(any(target_os = "linux",
+          target_os = "android",
+          target_os = "emscripten",
+          target_os = "fuchsia",
+          any(target_os = "wasi", target_env = "wasi"),
+          target_os = "freebsd"))]
+mod test_posix_fallocate {
+
+    use tempfile::NamedTempFile;
+    use std::{io::Read, os::unix::io::{RawFd, AsRawFd}};
+    use nix::errno::Errno;
+    use nix::fcntl::*;
+    use nix::unistd::pipe;
+
+    #[test]
+    fn success() {
+        const LEN: usize = 100;
+        let mut tmp = NamedTempFile::new().unwrap();
+        let fd = tmp.as_raw_fd();
+        let res = posix_fallocate(fd, 0, LEN as libc::off_t);
+        match res {
+            Ok(_) => {
+                let mut data = [1u8; LEN];
+                assert_eq!(tmp.read(&mut data).expect("read failure"), LEN);
+                assert_eq!(&data[..], &[0u8; LEN][..]);
+            }
+            Err(nix::Error::Sys(Errno::EINVAL)) => {
+                // POSIX requires posix_fallocate to return EINVAL both for
+                // invalid arguments (i.e. len < 0) and if the operation is not
+                // supported by the file system.
+                // There's no way to tell for sure whether the file system
+                // supports posix_fallocate, so we must pass the test if it
+                // returns EINVAL.
+            }
+            _ => res.unwrap(),
+        }
+    }
+
+    #[test]
+    fn errno() {
+        let (rd, _wr) = pipe().unwrap();
+        let err = posix_fallocate(rd as RawFd, 0, 100).unwrap_err();
+        use nix::Error::Sys;
+        match err {
+            Sys(Errno::EINVAL)
+                | Sys(Errno::ENODEV)
+                | Sys(Errno::ESPIPE)
+                | Sys(Errno::EBADF) => (),
+            errno =>
+                panic!(
+                    "unexpected errno {}",
+                    errno,
+                ),
+        }
+    }
+}