chrdev: Pass offset to read

Author: geofft

src/chrdev.rs

@@ -1,4 +1,4 @@
-use core::convert::TryInto;
+use core::convert::{TryFrom, TryInto};
 use core::ops::Range;
 use core::{mem, ptr};
 
@@ -139,17 +139,22 @@ unsafe extern "C" fn read_callback<T: FileOperations>(
 ) -> c_types::c_ssize_t {
     let mut data = match UserSlicePtr::new(buf as *mut c_types::c_void, len) {
         Ok(ptr) => ptr.writer(),
-        Err(e) => return e.to_kernel_errno() as c_types::c_ssize_t,
+        Err(e) => return e.to_kernel_errno().try_into().unwrap(),
     };
     let f = &*((*file).private_data as *const T);
-    // TODO: Pass offset to read()?
-    match f.read(&mut data) {
+    // 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.read(&mut data, positive_offset) {
         Ok(()) => {
             let written = len - data.len();
-            (*offset) += written as bindings::loff_t;
-            written as c_types::c_ssize_t
+            (*offset) += bindings::loff_t::try_from(written).unwrap();
+            written.try_into().unwrap()
         }
-        Err(e) => e.to_kernel_errno() as c_types::c_ssize_t,
+        Err(e) => e.to_kernel_errno().try_into().unwrap(),
     }
 }
 
@@ -236,7 +241,7 @@ pub trait FileOperations: Sync + Sized {
     const VTABLE: FileOperationsVtable;
 
     fn open() -> KernelResult<Self>;
-    fn read(&self, _buf: &mut UserSlicePtrWriter) -> KernelResult<()> {
+    fn read(&self, _buf: &mut UserSlicePtrWriter, _offset: u64) -> KernelResult<()> {
         Err(Error::EINVAL)
     }
     fn seek(&self, _file: &File, _offset: SeekFrom) -> KernelResult<u64> {

tests/chrdev/src/lib.rs

@@ -16,8 +16,14 @@ impl linux_kernel_module::chrdev::FileOperations for CycleFile {
     fn read(
         &self,
         buf: &mut linux_kernel_module::user_ptr::UserSlicePtrWriter,
+        offset: u64,
     ) -> linux_kernel_module::KernelResult<()> {
-        for c in b"123456789".iter().cycle().take(buf.len()) {
+        for c in b"123456789"
+            .iter()
+            .cycle()
+            .skip((offset % 9) as _)
+            .take(buf.len())
+        {
             buf.write(&[*c])?;
         }
         return Ok(());

tests/chrdev/tests/tests.rs

@@ -1,5 +1,6 @@
 use std::fs;
 use std::io::{Read, Seek, SeekFrom};
+use std::os::unix::prelude::FileExt;
 use std::path::PathBuf;
 use std::process::Command;
 
@@ -78,6 +79,36 @@ fn test_read() {
     });
 }
 
+#[test]
+fn test_read_offset() {
+    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::File::open(&p).unwrap();
+        let mut data = [0; 5];
+        f.read_exact(&mut data).unwrap();
+        assert_eq!(&data, b"12345");
+        f.read_exact(&mut data).unwrap();
+        assert_eq!(&data, b"67891");
+    });
+}
+
+#[test]
+fn test_read_at() {
+    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 f = fs::File::open(&p).unwrap();
+        let mut data = [0; 5];
+        f.read_exact_at(&mut data, 7).unwrap();
+        assert_eq!(&data, b"89123");
+    });
+}
+
 #[test]
 fn test_read_unimplemented() {
     with_kernel_module(|| {