Add lseek samples in Rust MiscDevice samples
Signed-off-by: Ryosuke Yasuoka <ryasuoka@redhat.com>
---
samples/rust/rust_misc_device.rs | 68 ++++++++++++++++++++++++++++++++
1 file changed, 68 insertions(+)
diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
index e7ab77448f75..991a59a3ea16 100644
--- a/samples/rust/rust_misc_device.rs
+++ b/samples/rust/rust_misc_device.rs
@@ -86,6 +86,33 @@
//! return -1;
//! }
//!
+//! // Set a file offset
+//! printf("Call lseek SEEK_SET\n");
+//! ret = lseek(fd, 10, SEEK_SET);
+//! if (ret == 10)
+//! printf("lseek: Succeed to SEEK_SET\n");
+//! else
+//! printf("lseek: Failed to SEEK_SET\n");
+//!
+//! // Change the file offset from the initial value
+//! printf("Call lseek SEEK_CUR\n");
+//! ret = lseek(fd, 10, SEEK_CUR);
+//! if (ret == 20)
+//! printf("lseek: Succeed to SEEK_CUR\n");
+//! else
+//! printf("lseek: Failed to SEEK_CUR\n");
+//!
+//! // i_size is 0. So the following task always should fail.
+//! printf("Call lseek SEEK_END\n");
+//! ret = lseek(fd, -10, SEEK_END);
+//! if (ret < 0)
+//! perror("lseek: Succeeded to fail - this was expected");
+//! else {
+//! printf("lseek: Failed to fail SEEK_END\n");
+//! close(fd);
+//! return -1;
+//! }
+//!
//! // Close the device file
//! printf("Closing /dev/rust-misc-device\n");
//! close(fd);
@@ -114,6 +141,10 @@
const RUST_MISC_DEV_GET_VALUE: u32 = _IOR::<i32>('|' as u32, 0x81);
const RUST_MISC_DEV_SET_VALUE: u32 = _IOW::<i32>('|' as u32, 0x82);
+const SEEK_SET: i32 = 0;
+const SEEK_CUR: i32 = 1;
+const SEEK_END: i32 = 2;
+
module! {
type: RustMiscDeviceModule,
name: "rust_misc_device",
@@ -173,6 +204,43 @@ fn open(_file: &File, misc: &MiscDeviceRegistration<Self>) -> Result<Pin<KBox<Se
)
}
+ fn llseek(me: Pin<&RustMiscDevice>, file: &File, offset: i64, whence: i32) -> Result<isize> {
+ dev_info!(me.dev, "LLSEEK Rust Misc Device Sample\n");
+ let pos: i64;
+ let eof: i64;
+
+ // SAFETY:
+ // * The file is valid for the duration of this call.
+ // * f_inode must be valid while the file is valid.
+ unsafe {
+ pos = (*file.as_ptr()).f_pos;
+ eof = (*(*file.as_ptr()).f_inode).i_size;
+ }
+
+ let new_pos = match whence {
+ SEEK_SET => offset,
+ SEEK_CUR => pos + offset,
+ SEEK_END => eof + offset,
+ _ => {
+ dev_err!(me.dev, "LLSEEK does not recognised: {}.\n", whence);
+ return Err(EINVAL);
+ }
+ };
+
+ if new_pos < 0 {
+ dev_err!(me.dev, "The file offset becomes negative: {}.\n", new_pos);
+ return Err(EINVAL);
+ }
+
+ // SAFETY: The file is valid for the duration of this call.
+ let ret: isize = unsafe {
+ (*file.as_ptr()).f_pos = new_pos;
+ new_pos as isize
+ };
+
+ Ok(ret)
+ }
+
fn ioctl(me: Pin<&RustMiscDevice>, _file: &File, cmd: u32, arg: usize) -> Result<isize> {
dev_info!(me.dev, "IOCTLing Rust Misc Device Sample\n");
--
2.50.1On Mon Aug 18, 2025 at 3:58 PM CEST, Ryosuke Yasuoka wrote:
> + fn llseek(me: Pin<&RustMiscDevice>, file: &File, offset: i64, whence: i32) -> Result<isize> {
> + dev_info!(me.dev, "LLSEEK Rust Misc Device Sample\n");
> + let pos: i64;
> + let eof: i64;
> +
> + // SAFETY:
> + // * The file is valid for the duration of this call.
> + // * f_inode must be valid while the file is valid.
> + unsafe {
> + pos = (*file.as_ptr()).f_pos;
> + eof = (*(*file.as_ptr()).f_inode).i_size;
> + }
Please include abstractions for writing & reading the file position
instead of using `unsafe`.
---
Cheers,
Benno
> +
> + let new_pos = match whence {
> + SEEK_SET => offset,
> + SEEK_CUR => pos + offset,
> + SEEK_END => eof + offset,
> + _ => {
> + dev_err!(me.dev, "LLSEEK does not recognised: {}.\n", whence);
> + return Err(EINVAL);
> + }
> + };
> +
> + if new_pos < 0 {
> + dev_err!(me.dev, "The file offset becomes negative: {}.\n", new_pos);
> + return Err(EINVAL);
> + }
> +
> + // SAFETY: The file is valid for the duration of this call.
> + let ret: isize = unsafe {
> + (*file.as_ptr()).f_pos = new_pos;
> + new_pos as isize
> + };
> +
> + Ok(ret)
> + }
> +
> fn ioctl(me: Pin<&RustMiscDevice>, _file: &File, cmd: u32, arg: usize) -> Result<isize> {
> dev_info!(me.dev, "IOCTLing Rust Misc Device Sample\n");
>
On Tue, Aug 19, 2025 at 12:05:41AM +0200, Benno Lossin wrote:
> On Mon Aug 18, 2025 at 3:58 PM CEST, Ryosuke Yasuoka wrote:
> > + fn llseek(me: Pin<&RustMiscDevice>, file: &File, offset: i64, whence: i32) -> Result<isize> {
> > + dev_info!(me.dev, "LLSEEK Rust Misc Device Sample\n");
> > + let pos: i64;
> > + let eof: i64;
> > +
> > + // SAFETY:
> > + // * The file is valid for the duration of this call.
> > + // * f_inode must be valid while the file is valid.
> > + unsafe {
> > + pos = (*file.as_ptr()).f_pos;
> > + eof = (*(*file.as_ptr()).f_inode).i_size;
> > + }
>
> Please include abstractions for writing & reading the file position
> instead of using `unsafe`.
OK. I believe I probably need to modify on the kernel:fs::file::File to
add abstraction for writing & reading. I'll re-consider and send them in
v2 patch.
Thank you very much for your comment.
> ---
> Cheers,
> Benno
>
> > +
> > + let new_pos = match whence {
> > + SEEK_SET => offset,
> > + SEEK_CUR => pos + offset,
> > + SEEK_END => eof + offset,
> > + _ => {
> > + dev_err!(me.dev, "LLSEEK does not recognised: {}.\n", whence);
> > + return Err(EINVAL);
> > + }
> > + };
> > +
> > + if new_pos < 0 {
> > + dev_err!(me.dev, "The file offset becomes negative: {}.\n", new_pos);
> > + return Err(EINVAL);
> > + }
> > +
> > + // SAFETY: The file is valid for the duration of this call.
> > + let ret: isize = unsafe {
> > + (*file.as_ptr()).f_pos = new_pos;
> > + new_pos as isize
> > + };
> > +
> > + Ok(ret)
> > + }
> > +
> > fn ioctl(me: Pin<&RustMiscDevice>, _file: &File, cmd: u32, arg: usize) -> Result<isize> {
> > dev_info!(me.dev, "IOCTLing Rust Misc Device Sample\n");
> >
>
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