Auto merge of rust-lang#89518 - a1phyr:unix_file_vectored_at, r=workingjubilee

Add vectored positioned I/O on Unix

Add methods for vectored I/O with an offset on `File` for `unix` under `#![feature(unix_file_vectored_at)]`.

The new methods are wrappers around `preadv` and `pwritev`.

Tracking issue: rust-lang#89517

Author: bors

library/std/src/os/unix/fs.rs

@@ -17,6 +17,10 @@ use crate::sealed::Sealed;
 #[allow(unused_imports)]
 use io::{Read, Write};
 
+// Tests for this module
+#[cfg(test)]
+mod tests;
+
 /// Unix-specific extensions to [`fs::File`].
 #[stable(feature = "file_offset", since = "1.15.0")]
 pub trait FileExt {
@@ -54,6 +58,16 @@ pub trait FileExt {
     #[stable(feature = "file_offset", since = "1.15.0")]
     fn read_at(&self, buf: &mut [u8], offset: u64) -> io::Result<usize>;
 
+    /// Like `read_at`, except that it reads into a slice of buffers.
+    ///
+    /// Data is copied to fill each buffer in order, with the final buffer
+    /// written to possibly being only partially filled. This method must behave
+    /// equivalently to a single call to read with concatenated buffers.
+    #[unstable(feature = "unix_file_vectored_at", issue = "89517")]
+    fn read_vectored_at(&self, bufs: &mut [io::IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
+        io::default_read_vectored(|b| self.read_at(b, offset), bufs)
+    }
+
     /// Reads the exact number of byte required to fill `buf` from the given offset.
     ///
     /// The offset is relative to the start of the file and thus independent
@@ -155,6 +169,16 @@ pub trait FileExt {
     #[stable(feature = "file_offset", since = "1.15.0")]
     fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize>;
 
+    /// Like `write_at`, except that it writes from a slice of buffers.
+    ///
+    /// Data is copied from each buffer in order, with the final buffer read
+    /// from possibly being only partially consumed. This method must behave as
+    /// a call to `write_at` with the buffers concatenated would.
+    #[unstable(feature = "unix_file_vectored_at", issue = "89517")]
+    fn write_vectored_at(&self, bufs: &[io::IoSlice<'_>], offset: u64) -> io::Result<usize> {
+        io::default_write_vectored(|b| self.write_at(b, offset), bufs)
+    }
+
     /// Attempts to write an entire buffer starting from a given offset.
     ///
     /// The offset is relative to the start of the file and thus independent
@@ -218,9 +242,15 @@ impl FileExt for fs::File {
     fn read_at(&self, buf: &mut [u8], offset: u64) -> io::Result<usize> {
         self.as_inner().read_at(buf, offset)
     }
+    fn read_vectored_at(&self, bufs: &mut [io::IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
+        self.as_inner().read_vectored_at(bufs, offset)
+    }
     fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize> {
         self.as_inner().write_at(buf, offset)
     }
+    fn write_vectored_at(&self, bufs: &[io::IoSlice<'_>], offset: u64) -> io::Result<usize> {
+        self.as_inner().write_vectored_at(bufs, offset)
+    }
 }
 
 /// Unix-specific extensions to [`fs::Permissions`].

library/std/src/os/unix/fs/tests.rs

@@ -0,0 +1,57 @@
+use super::*;
+
+#[test]
+fn read_vectored_at() {
+    let msg = b"preadv is working!";
+    let dir = crate::sys_common::io::test::tmpdir();
+
+    let filename = dir.join("preadv.txt");
+    {
+        let mut file = fs::File::create(&filename).unwrap();
+        file.write_all(msg).unwrap();
+    }
+    {
+        let file = fs::File::open(&filename).unwrap();
+        let mut buf0 = [0; 4];
+        let mut buf1 = [0; 3];
+
+        let mut iovec = [io::IoSliceMut::new(&mut buf0), io::IoSliceMut::new(&mut buf1)];
+
+        let n = file.read_vectored_at(&mut iovec, 4).unwrap();
+
+        assert!(n == 4 || n == 7);
+        assert_eq!(&buf0, b"dv i");
+
+        if n == 7 {
+            assert_eq!(&buf1, b"s w");
+        }
+    }
+}
+
+#[test]
+fn write_vectored_at() {
+    let msg = b"pwritev is not working!";
+    let dir = crate::sys_common::io::test::tmpdir();
+
+    let filename = dir.join("preadv.txt");
+    {
+        let mut file = fs::File::create(&filename).unwrap();
+        file.write_all(msg).unwrap();
+    }
+    let expected = {
+        let file = fs::File::options().write(true).open(&filename).unwrap();
+        let buf0 = b"    ";
+        let buf1 = b"great  ";
+
+        let iovec = [io::IoSlice::new(buf0), io::IoSlice::new(buf1)];
+
+        let n = file.write_vectored_at(&iovec, 11).unwrap();
+
+        assert!(n == 4 || n == 11);
+
+        if n == 4 { b"pwritev is     working!" } else { b"pwritev is     great  !" }
+    };
+
+    let content = fs::read(&filename).unwrap();
+    assert_eq!(&content, expected);
+}

library/std/src/sys/unix/fd.rs

@@ -98,7 +98,7 @@ impl FileDesc {
         let ret = cvt(unsafe {
             libc::readv(
                 self.as_raw_fd(),
-                bufs.as_ptr() as *const libc::iovec,
+                bufs.as_mut_ptr() as *mut libc::iovec as *const libc::iovec,
                 cmp::min(bufs.len(), max_iov()) as libc::c_int,
             )
         })?;
@@ -107,7 +107,7 @@ impl FileDesc {
 
     #[cfg(any(target_os = "espidf", target_os = "horizon"))]
     pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
-        return crate::io::default_read_vectored(|b| self.read(b), bufs);
+        io::default_read_vectored(|b| self.read(b), bufs)
     }
 
     #[inline]
@@ -153,6 +153,95 @@ impl FileDesc {
         Ok(())
     }
 
+    #[cfg(any(
+        target_os = "emscripten",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "netbsd",
+    ))]
+    pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
+        let ret = cvt(unsafe {
+            libc::preadv(
+                self.as_raw_fd(),
+                bufs.as_mut_ptr() as *mut libc::iovec as *const libc::iovec,
+                cmp::min(bufs.len(), max_iov()) as libc::c_int,
+                offset as _,
+            )
+        })?;
+        Ok(ret as usize)
+    }
+
+    #[cfg(not(any(
+        target_os = "android",
+        target_os = "emscripten",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "ios",
+        target_os = "linux",
+        target_os = "macos",
+        target_os = "netbsd",
+    )))]
+    pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
+        io::default_read_vectored(|b| self.read_at(b, offset), bufs)
+    }
+
+    // We support some old Android versions that do not have `preadv` in libc,
+    // so we use weak linkage and fallback to a direct syscall if not available.
+    //
+    // On 32-bit targets, we don't want to deal with weird ABI issues around
+    // passing 64-bits parameters to syscalls, so we fallback to the default
+    // implementation if `preadv` is not available.
+    #[cfg(all(target_os = "android", target_pointer_width = "64"))]
+    pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
+        super::weak::syscall! {
+            fn preadv(
+                fd: libc::c_int,
+                iovec: *const libc::iovec,
+                n_iovec: libc::c_int,
+                offset: off64_t
+            ) -> isize
+        }
+
+        let ret = cvt(unsafe {
+            preadv(
+                self.as_raw_fd(),
+                bufs.as_mut_ptr() as *mut libc::iovec as *const libc::iovec,
+                cmp::min(bufs.len(), max_iov()) as libc::c_int,
+                offset as _,
+            )
+        })?;
+        Ok(ret as usize)
+    }
+
+    // We support old MacOS and iOS versions that do not have `preadv`. There is
+    // no `syscall` possible in these platform.
+    #[cfg(any(
+        all(target_os = "android", target_pointer_width = "32"),
+        target_os = "ios",
+        target_os = "macos",
+    ))]
+    pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
+        super::weak::weak!(fn preadv64(libc::c_int, *const libc::iovec, libc::c_int, off64_t) -> isize);
+
+        match preadv64.get() {
+            Some(preadv) => {
+                let ret = cvt(unsafe {
+                    preadv(
+                        self.as_raw_fd(),
+                        bufs.as_mut_ptr() as *mut libc::iovec as *const libc::iovec,
+                        cmp::min(bufs.len(), max_iov()) as libc::c_int,
+                        offset as _,
+                    )
+                })?;
+                Ok(ret as usize)
+            }
+            None => io::default_read_vectored(|b| self.read_at(b, offset), bufs),
+        }
+    }
+
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         let ret = cvt(unsafe {
             libc::write(
@@ -178,7 +267,7 @@ impl FileDesc {
 
     #[cfg(any(target_os = "espidf", target_os = "horizon"))]
     pub fn write_vectored(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
-        return crate::io::default_write_vectored(|b| self.write(b), bufs);
+        io::default_write_vectored(|b| self.write(b), bufs)
     }
 
     #[inline]
@@ -203,6 +292,95 @@ impl FileDesc {
         }
     }
 
+    #[cfg(any(
+        target_os = "emscripten",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "netbsd",
+    ))]
+    pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
+        let ret = cvt(unsafe {
+            libc::pwritev(
+                self.as_raw_fd(),
+                bufs.as_ptr() as *const libc::iovec,
+                cmp::min(bufs.len(), max_iov()) as libc::c_int,
+                offset as _,
+            )
+        })?;
+        Ok(ret as usize)
+    }
+
+    #[cfg(not(any(
+        target_os = "android",
+        target_os = "emscripten",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "ios",
+        target_os = "linux",
+        target_os = "macos",
+        target_os = "netbsd",
+    )))]
+    pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
+        io::default_write_vectored(|b| self.write_at(b, offset), bufs)
+    }
+
+    // We support some old Android versions that do not have `pwritev` in libc,
+    // so we use weak linkage and fallback to a direct syscall if not available.
+    //
+    // On 32-bit targets, we don't want to deal with weird ABI issues around
+    // passing 64-bits parameters to syscalls, so we fallback to the default
+    // implementation if `pwritev` is not available.
+    #[cfg(all(target_os = "android", target_pointer_width = "64"))]
+    pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
+        super::weak::syscall! {
+            fn pwritev(
+                fd: libc::c_int,
+                iovec: *const libc::iovec,
+                n_iovec: libc::c_int,
+                offset: off64_t
+            ) -> isize
+        }
+
+        let ret = cvt(unsafe {
+            pwritev(
+                self.as_raw_fd(),
+                bufs.as_ptr() as *const libc::iovec,
+                cmp::min(bufs.len(), max_iov()) as libc::c_int,
+                offset as _,
+            )
+        })?;
+        Ok(ret as usize)
+    }
+
+    // We support old MacOS and iOS versions that do not have `pwritev`. There is
+    // no `syscall` possible in these platform.
+    #[cfg(any(
+        all(target_os = "android", target_pointer_width = "32"),
+        target_os = "ios",
+        target_os = "macos",
+    ))]
+    pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
+        super::weak::weak!(fn pwritev64(libc::c_int, *const libc::iovec, libc::c_int, off64_t) -> isize);
+
+        match pwritev64.get() {
+            Some(pwritev) => {
+                let ret = cvt(unsafe {
+                    pwritev(
+                        self.as_raw_fd(),
+                        bufs.as_ptr() as *const libc::iovec,
+                        cmp::min(bufs.len(), max_iov()) as libc::c_int,
+                        offset as _,
+                    )
+                })?;
+                Ok(ret as usize)
+            }
+            None => io::default_write_vectored(|b| self.write_at(b, offset), bufs),
+        }
+    }
+
     #[cfg(not(any(
         target_env = "newlib",
         target_os = "solaris",

library/std/src/sys/unix/fs.rs

@@ -1132,6 +1132,10 @@ impl File {
         self.0.read_buf(cursor)
     }
 
+    pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
+        self.0.read_vectored_at(bufs, offset)
+    }
+
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         self.0.write(buf)
     }
@@ -1149,6 +1153,10 @@ impl File {
         self.0.write_at(buf, offset)
     }
 
+    pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
+        self.0.write_vectored_at(bufs, offset)
+    }
+
     pub fn flush(&self) -> io::Result<()> {
         Ok(())
     }