file_traits.rs

// Copyright 2022 The ChromiumOS Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use std::fs::File;
use std::io::Error;
use std::io::Result;

use crate::descriptor::AsRawDescriptor;
use crate::FileAllocate;
use crate::FileReadWriteAtVolatile;
use crate::FileReadWriteVolatile;
use crate::VolatileSlice;
use crate::WriteZeroesAt;

impl FileReadWriteVolatile for File {
    fn read_volatile(&mut self, slice: VolatileSlice) -> Result<usize> {
        let mut bytes = 0;
        // SAFETY:
        // Safe because only bytes inside the slice are accessed and the kernel is expected
        // to handle arbitrary memory for I/O.
        let ret = unsafe {
            winapi::um::fileapi::ReadFile(
                self.as_raw_descriptor(),
                slice.as_ptr() as *mut libc::c_void,
                slice.size().try_into().unwrap(),
                &mut bytes,
                std::ptr::null_mut(),
            )
        };

        if ret > 0 {
            Ok(bytes as usize)
        } else {
            Err(Error::last_os_error())
        }
    }

    fn read_vectored_volatile(&mut self, bufs: &[VolatileSlice]) -> Result<usize> {
        if bufs.is_empty() {
            return Ok(0);
        }

        // Windows has ReadFileScatter, but that requires the buffers to all be the same
        // size and aligned to a page size boundary.
        // readv makes some guarantees that we can't guarantee in windows, like atomicity.
        let mut ret = 0usize;
        for buf in bufs.iter() {
            match self.read_volatile(*buf) {
                Ok(bytes) => ret += bytes,
                Err(_) => return Err(Error::last_os_error()),
            }
        }

        Ok(ret)
    }

    fn write_volatile(&mut self, slice: VolatileSlice) -> Result<usize> {
        let mut bytes = 0;
        // SAFETY:
        // Safe because only bytes inside the slice are accessed and the kernel is expected
        // to handle arbitrary memory for I/O.
        let ret = unsafe {
            winapi::um::fileapi::WriteFile(
                self.as_raw_descriptor(),
                slice.as_ptr() as *mut libc::c_void,
                slice.size().try_into().unwrap(),
                &mut bytes,
                std::ptr::null_mut(),
            )
        };

        if ret > 0 {
            Ok(bytes as usize)
        } else {
            Err(Error::last_os_error())
        }
    }

    fn write_vectored_volatile(&mut self, bufs: &[VolatileSlice]) -> Result<usize> {
        if bufs.is_empty() {
            return Ok(0);
        }

        // Windows has WriteFileGather, but that requires the buffers to all be the same
        // size and aligned to a page size boundary, and only writes one page of data
        // from each buffer.
        // writev makes some guarantees that we can't guarantee in windows, like atomicity.
        let mut ret = 0usize;
        for buf in bufs.iter() {
            match self.write_volatile(*buf) {
                Ok(bytes) => ret += bytes,
                Err(_) => return Err(Error::last_os_error()),
            }
        }

        Ok(ret)
    }
}

impl FileReadWriteAtVolatile for File {
    fn read_at_volatile(&self, slice: VolatileSlice, offset: u64) -> Result<usize> {
        // The unix implementation uses pread, which doesn't modify the file
        // pointer. Windows doesn't have an option for that, unfortunately.

        let mut bytes = 0;

        // SAFETY:
        // Safe because only bytes inside the slice are accessed and the kernel is expected
        // to handle arbitrary memory for I/O.
        let ret = unsafe {
            let mut overlapped: winapi::um::minwinbase::OVERLAPPED = std::mem::zeroed();
            overlapped.u.s_mut().Offset = offset as u32;
            overlapped.u.s_mut().OffsetHigh = (offset >> 32) as u32;

            winapi::um::fileapi::ReadFile(
                self.as_raw_descriptor(),
                slice.as_ptr() as *mut libc::c_void,
                slice.size().try_into().unwrap(),
                &mut bytes,
                &mut overlapped,
            )
        };

        if ret > 0 {
            Ok(bytes as usize)
        } else {
            Err(Error::last_os_error())
        }
    }

    fn read_vectored_at_volatile(&self, bufs: &[VolatileSlice], offset: u64) -> Result<usize> {
        if bufs.is_empty() {
            return Ok(0);
        }

        // Windows has ReadFileScatter, but that requires the buffers to all be the same
        // size and aligned to a page size boundary.
        // preadv makes some guarantees that we can't guarantee in windows, like atomicity.
        let mut ret: usize = 0;
        for buf in bufs.iter() {
            match self.read_at_volatile(*buf, offset + ret as u64) {
                Ok(bytes) => ret += bytes,
                Err(_) => return Err(Error::last_os_error()),
            }
        }

        Ok(ret)
    }

    fn write_at_volatile(&self, slice: VolatileSlice, offset: u64) -> Result<usize> {
        // The unix implementation uses pwrite, which doesn't modify the file
        // pointer. Windows doesn't have an option for that, unfortunately.

        let mut bytes = 0;

        // SAFETY:
        // Safe because only bytes inside the slice are accessed and the kernel is expected
        // to handle arbitrary memory for I/O.
        let ret = unsafe {
            let mut overlapped: winapi::um::minwinbase::OVERLAPPED = std::mem::zeroed();
            overlapped.u.s_mut().Offset = offset as u32;
            overlapped.u.s_mut().OffsetHigh = (offset >> 32) as u32;

            winapi::um::fileapi::WriteFile(
                self.as_raw_descriptor(),
                slice.as_ptr() as *mut libc::c_void,
                slice.size().try_into().unwrap(),
                &mut bytes,
                &mut overlapped,
            )
        };

        if ret > 0 {
            Ok(bytes as usize)
        } else {
            Err(Error::last_os_error())
        }
    }

    fn write_vectored_at_volatile(&self, bufs: &[VolatileSlice], offset: u64) -> Result<usize> {
        if bufs.is_empty() {
            return Ok(0);
        }

        // Windows has WriteFileGather, but that requires the buffers to all be the same
        // size and aligned to a page size boundary, and only writes one page of data
        // from each buffer.
        // pwritev makes some guarantees that we can't guarantee in windows, like atomicity.
        let mut ret: usize = 0;
        for buf in bufs.iter() {
            match self.write_at_volatile(*buf, offset + ret as u64) {
                Ok(bytes) => ret += bytes,
                Err(_) => return Err(Error::last_os_error()),
            }
        }

        Ok(ret)
    }
}

impl FileAllocate for File {
    fn allocate(&self, offset: u64, len: u64) -> Result<()> {
        // The Windows equivalent of fallocate's default mode (allocate a zeroed block of space in a
        // file) is to just call write_zeros_at. There are not, at the time of writing, any syscalls
        // that will extend the file and zero the range while maintaining the disk allocation in a
        // more efficient manner.
        self.write_zeroes_all_at(offset, len as usize)
    }
}