Merge #1089

1089: implement posix_fadvise r=asomers a=kevinwern

See: 
https://github.com/CraneStation/wasi-common/issues/16
http://man7.org/linux/man-pages/man2/posix_fadvise.2.html

Conditional compilation derived from corresponding libc conditions:
Fuchsia:
https://github.com/rust-lang/libc/blob/0b02c4060a750983cebcccdf1f35a5ec4cdcf516/src/fuchsia/mod.rs#L3807
https://github.com/rust-lang/libc/blob/0e702c1b4e2e56788e8b67d3efd9c242807c3d4b/src/lib.rs#L104-L109

uClibc:
https://github.com/rust-lang/libc/blob/11c762c535cb43dda3d9d87a0845c55201a905fb/src/unix/uclibc/mod.rs#L1676
https://github.com/rust-lang/libc/blob/ce7e3a7e866dd7109a971b694a2bf58bd08f101a/src/unix/mod.rs#L1141-L1143
https://github.com/rust-lang/libc/blob/0e702c1b4e2e56788e8b67d3efd9c242807c3d4b/src/lib.rs#L116-L121

Linux, android, emscripten:
https://github.com/rust-lang/libc/blob/11c762c535cb43dda3d9d87a0845c55201a905fb/src/unix/linux_like/mod.rs#L1303
https://github.com/rust-lang/libc/blob/ce7e3a7e866dd7109a971b694a2bf58bd08f101a/src/unix/mod.rs#L1147-L1151
https://github.com/rust-lang/libc/blob/0e702c1b4e2e56788e8b67d3efd9c242807c3d4b/src/lib.rs#L116-L121

FreeBSD:
https://github.com/rust-lang/libc/blob/e0ff1e68b9e34173e9c4c3217d1b0fc81a7d352d/src/unix/bsd/freebsdlike/freebsd/mod.rs#L1223
https://github.com/rust-lang/libc/blob/ce7e3a7e866dd7109a971b694a2bf58bd08f101a/src/unix/bsd/freebsdlike/mod.rs#L1307-L1309
https://github.com/rust-lang/libc/blob/ce7e3a7e866dd7109a971b694a2bf58bd08f101a/src/unix/bsd/mod.rs#L683-L685
https://github.com/rust-lang/libc/blob/ce7e3a7e866dd7109a971b694a2bf58bd08f101a/src/unix/mod.rs#L1152-L1159
https://github.com/rust-lang/libc/blob/0e702c1b4e2e56788e8b67d3efd9c242807c3d4b/src/lib.rs#L116-L121

WASI:
https://github.com/rust-lang/libc/blob/0e702c1b4e2e56788e8b67d3efd9c242807c3d4b/src/wasi.rs#L1001
https://github.com/rust-lang/libc/blob/0e702c1b4e2e56788e8b67d3efd9c242807c3d4b/src/lib.rs#L134-L139


Co-authored-by: Kevin Wern <[email protected]>

Author: bors[bot]

CHANGELOG.md

@@ -13,6 +13,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#1069](https://github.com/nix-rust/nix/pull/1069))
 - Add `mkdirat`.
   ([#1084](https://github.com/nix-rust/nix/pull/1084))
+- Add `posix_fadvise`.
+  ([#1089](https://github.com/nix-rust/nix/pull/1089))
 
 ### Changed
 - Support for `ifaddrs` now present when building for Android.

src/fcntl.rs

@@ -12,6 +12,15 @@ use std::ptr; // For splice and copy_file_range
 #[cfg(any(target_os = "android", target_os = "linux"))]
 use sys::uio::IoVec;  // For vmsplice
 
+#[cfg(any(target_os = "linux",
+          target_os = "android",
+          target_os = "emscripten",
+          target_os = "fuchsia",
+          any(target_os = "wasi", target_env = "wasi"),
+          target_env = "uclibc",
+          target_env = "freebsd"))]
+pub use self::posix_fadvise::*;
+
 libc_bitflags!{
     pub struct AtFlags: c_int {
         AT_SYMLINK_NOFOLLOW;
@@ -448,3 +457,37 @@ pub fn fallocate(fd: RawFd, mode: FallocateFlags, offset: libc::off_t, len: libc
     let res = unsafe { libc::fallocate(fd, mode.bits(), offset, len) };
     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_env = "uclibc",
+          target_env = "freebsd"))]
+mod posix_fadvise {
+    use Result;
+    use libc;
+    use errno::Errno;
+    use std::os::unix::io::RawFd;
+
+    libc_enum! {
+        #[repr(i32)]
+        pub enum PosixFadviseAdvice {
+            POSIX_FADV_NORMAL,
+            POSIX_FADV_SEQUENTIAL,
+            POSIX_FADV_RANDOM,
+            POSIX_FADV_NOREUSE,
+            POSIX_FADV_WILLNEED,
+            POSIX_FADV_DONTNEED,
+        }
+    }
+
+    pub fn posix_fadvise(fd: RawFd,
+                         offset: libc::off_t,
+                         len: libc::off_t,
+                         advice: PosixFadviseAdvice) -> Result<libc::c_int> {
+        let res = unsafe { libc::posix_fadvise(fd, offset, len, advice as libc::c_int) };
+        Errno::result(res)
+    }
+}

test/test_fcntl.rs

@@ -180,3 +180,36 @@ mod linux_android {
         assert_eq!(100, read(fd, &mut buf).unwrap());
     }
 }
+
+#[cfg(any(target_os = "linux",
+          target_os = "android",
+          target_os = "emscripten",
+          target_os = "fuchsia",
+          any(target_os = "wasi", target_env = "wasi"),
+          target_env = "uclibc",
+          target_env = "freebsd"))]
+mod test_posix_fadvise {
+
+    use tempfile::NamedTempFile;
+    use std::os::unix::io::{RawFd, AsRawFd};
+    use nix::errno::Errno;
+    use nix::fcntl::*;
+    use nix::unistd::pipe;
+
+    #[test]
+    fn test_success() {
+        let tmp = NamedTempFile::new().unwrap();
+        let fd = tmp.as_raw_fd();
+        let res = posix_fadvise(fd, 0, 100, PosixFadviseAdvice::POSIX_FADV_WILLNEED).unwrap();
+
+        assert_eq!(res, 0);
+    }
+
+    #[test]
+    fn test_errno() {
+        let (rd, _wr) = pipe().unwrap();
+        let errno = posix_fadvise(rd as RawFd, 0, 100, PosixFadviseAdvice::POSIX_FADV_WILLNEED)
+                                 .unwrap();
+        assert_eq!(errno, Errno::ESPIPE as i32);
+    }
+}