Refs #164 -- added write support to FileOperations

Author: alex

src/file_operations.rs

@@ -6,7 +6,7 @@ use alloc::boxed::Box;
 use crate::bindings;
 use crate::c_types;
 use crate::error::{Error, KernelResult};
-use crate::user_ptr::{UserSlicePtr, UserSlicePtrWriter};
+use crate::user_ptr::{UserSlicePtr, UserSlicePtrReader, UserSlicePtrWriter};
 
 pub struct File {
     ptr: *const bindings::file,
@@ -70,6 +70,33 @@ unsafe extern "C" fn read_callback<T: Read>(
     }
 }
 
+unsafe extern "C" fn write_callback<T: Write>(
+    file: *mut bindings::file,
+    buf: *const c_types::c_char,
+    len: c_types::c_size_t,
+    offset: *mut bindings::loff_t,
+) -> c_types::c_ssize_t {
+    let mut data = match UserSlicePtr::new(buf as *mut c_types::c_void, len) {
+        Ok(ptr) => ptr.reader(),
+        Err(e) => return e.to_kernel_errno().try_into().unwrap(),
+    };
+    let f = &*((*file).private_data as *const T);
+    // No FMODE_UNSIGNED_OFFSET support, so offset must be in [0, 2^63).
+    // See discussion in #113
+    let positive_offset = match (*offset).try_into() {
+        Ok(v) => v,
+        Err(_) => return Error::EINVAL.to_kernel_errno().try_into().unwrap(),
+    };
+    match f.write(&mut data, positive_offset) {
+        Ok(()) => {
+            let read = len - data.len();
+            (*offset) += bindings::loff_t::try_from(read).unwrap();
+            read.try_into().unwrap()
+        }
+        Err(e) => e.to_kernel_errno().try_into().unwrap(),
+    }
+}
+
 unsafe extern "C" fn release_callback<T: FileOperations>(
     _inode: *mut bindings::inode,
     file: *mut bindings::file,
@@ -168,6 +195,13 @@ impl<T: Read> FileOperationsVtableBuilder<T> {
     }
 }
 
+impl<T: Write> FileOperationsVtableBuilder<T> {
+    pub const fn write(mut self) -> FileOperationsVtableBuilder<T> {
+        self.0.write = Some(write_callback::<T>);
+        self
+    }
+}
+
 impl<T: Seek> FileOperationsVtableBuilder<T> {
     pub const fn seek(mut self) -> FileOperationsVtableBuilder<T> {
         self.0.llseek = Some(llseek_callback::<T>);
@@ -199,6 +233,12 @@ pub trait Read {
     fn read(&self, buf: &mut UserSlicePtrWriter, offset: u64) -> KernelResult<()>;
 }
 
+pub trait Write {
+    /// Writes data from userspace o this file. Corresponds to the `write`
+    /// function pointer in `struct file_operations`.
+    fn write(&self, buf: &mut UserSlicePtrReader, offset: u64) -> KernelResult<()>;
+}
+
 pub trait Seek {
     /// Changes the position of the file. Corresponds to the `llseek` function
     /// pointer in `struct file_operations`.

src/user_ptr.rs

@@ -66,9 +66,7 @@ impl UserSlicePtr {
     /// Returns EFAULT if the address does not currently point to
     /// mapped, readable memory.
     pub fn read_all(self) -> error::KernelResult<Vec<u8>> {
-        let mut data = vec![0; self.1];
-        self.reader().read(&mut data)?;
-        Ok(data)
+        self.reader().read_all()
     }
 
     /// Construct a `UserSlicePtrReader` that can incrementally read
@@ -97,6 +95,27 @@ impl UserSlicePtr {
 pub struct UserSlicePtrReader(*mut c_types::c_void, usize);
 
 impl UserSlicePtrReader {
+    /// Returns the number of bytes left to be read from this. Note that even
+    /// reading less than this number of bytes may return an Error().
+    pub fn len(&self) -> usize {
+        self.1
+    }
+
+    /// Returns `true` if `self.len()` is 0.
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Read all data remaining in the user slice and return it in a `Vec`.
+    ///
+    /// Returns EFAULT if the address does not currently point to
+    /// mapped, readable memory.
+    pub fn read_all(&mut self) -> error::KernelResult<Vec<u8>> {
+        let mut data = vec![0; self.1];
+        self.read(&mut data)?;
+        Ok(data)
+    }
+
     pub fn read(&mut self, data: &mut [u8]) -> error::KernelResult<()> {
         if data.len() > self.1 || data.len() > u32::MAX as usize {
             return Err(error::Error::EFAULT);

tests/chrdev/src/lib.rs

@@ -1,5 +1,8 @@
 #![no_std]
 
+use alloc::string::ToString;
+use core::sync::atomic::{AtomicUsize, Ordering};
+
 use linux_kernel_module::{self, cstr};
 
 struct CycleFile;
@@ -55,16 +58,59 @@ impl linux_kernel_module::file_operations::Seek for SeekFile {
     }
 }
 
+struct WriteFile {
+    written: AtomicUsize,
+}
+
+impl linux_kernel_module::file_operations::FileOperations for WriteFile {
+    const VTABLE: linux_kernel_module::file_operations::FileOperationsVtable =
+        linux_kernel_module::file_operations::FileOperationsVtable::builder::<Self>()
+            .read()
+            .write()
+            .build();
+
+    fn open() -> linux_kernel_module::KernelResult<Self> {
+        return Ok(WriteFile {
+            written: AtomicUsize::new(0),
+        });
+    }
+}
+
+impl linux_kernel_module::file_operations::Read for WriteFile {
+    fn read(
+        &self,
+        buf: &mut linux_kernel_module::user_ptr::UserSlicePtrWriter,
+        _offset: u64,
+    ) -> linux_kernel_module::KernelResult<()> {
+        let val = self.written.load(Ordering::SeqCst).to_string();
+        buf.write(val.as_bytes())?;
+        return Ok(());
+    }
+}
+
+impl linux_kernel_module::file_operations::Write for WriteFile {
+    fn write(
+        &self,
+        buf: &mut linux_kernel_module::user_ptr::UserSlicePtrReader,
+        _offset: u64,
+    ) -> linux_kernel_module::KernelResult<()> {
+        let data = buf.read_all()?;
+        self.written.fetch_add(data.len(), Ordering::SeqCst);
+        return Ok(());
+    }
+}
+
 struct ChrdevTestModule {
     _chrdev_registration: linux_kernel_module::chrdev::Registration,
 }
 
 impl linux_kernel_module::KernelModule for ChrdevTestModule {
     fn init() -> linux_kernel_module::KernelResult<Self> {
         let chrdev_registration =
-            linux_kernel_module::chrdev::builder(cstr!("chrdev-tests"), 0..2)?
+            linux_kernel_module::chrdev::builder(cstr!("chrdev-tests"), 0..3)?
                 .register_device::<CycleFile>()
                 .register_device::<SeekFile>()
+                .register_device::<WriteFile>()
                 .build()?;
         Ok(ChrdevTestModule {
             _chrdev_registration: chrdev_registration,

tests/chrdev/tests/tests.rs

@@ -1,5 +1,5 @@
 use std::fs;
-use std::io::{Read, Seek, SeekFrom};
+use std::io::{Read, Seek, SeekFrom, Write};
 use std::os::unix::prelude::FileExt;
 use std::path::PathBuf;
 use std::process::Command;
@@ -45,6 +45,7 @@ impl Drop for UnlinkOnDrop<'_> {
 fn mknod(path: &PathBuf, major: libc::dev_t, minor: libc::dev_t) -> UnlinkOnDrop {
     Command::new("sudo")
         .arg("mknod")
+        .arg("--mode=a=rw")
         .arg(path.to_str().unwrap())
         .arg("c")
         .arg(major.to_string())
@@ -56,6 +57,7 @@ fn mknod(path: &PathBuf, major: libc::dev_t, minor: libc::dev_t) -> UnlinkOnDrop
 
 const READ_FILE_MINOR: libc::dev_t = 0;
 const SEEK_FILE_MINOR: libc::dev_t = 1;
+const WRITE_FILE_MINOR: libc::dev_t = 2;
 
 #[test]
 fn test_mknod() {
@@ -178,3 +180,44 @@ fn test_lseek() {
         );
     });
 }
+
+#[test]
+fn test_write_unimplemented() {
+    with_kernel_module(|| {
+        let device_number = get_device_major_number();
+        let p = temporary_file_path();
+        let _u = mknod(&p, device_number, READ_FILE_MINOR);
+
+        let mut f = fs::OpenOptions::new().write(true).open(&p).unwrap();
+        assert_eq!(
+            f.write(&[1, 2, 3]).unwrap_err().raw_os_error().unwrap(),
+            libc::EBADF
+        );
+    })
+}
+
+#[test]
+fn test_write() {
+    with_kernel_module(|| {
+        let device_number = get_device_major_number();
+        let p = temporary_file_path();
+        let _u = mknod(&p, device_number, WRITE_FILE_MINOR);
+
+        let mut f = fs::OpenOptions::new()
+            .read(true)
+            .write(true)
+            .open(&p)
+            .unwrap();
+        assert_eq!(f.write(&[1, 2, 3]).unwrap(), 3);
+
+        let mut buf = [0; 1];
+        f.read_exact(&mut buf).unwrap();
+        assert_eq!(&buf, b"3");
+
+        assert_eq!(f.write(&[1, 2, 3, 4, 5]).unwrap(), 5);
+
+        let mut buf = [0; 1];
+        f.read_exact(&mut buf).unwrap();
+        assert_eq!(&buf, b"8");
+    })
+}