[PATCH rust-next v2 3/3] rust: samples: miscdevice: add lseek samples

Ryosuke Yasuoka
2025-10-15T04:03:36Z

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 d69bc33dbd99..7f227deef69d 100644
--- a/samples/rust/rust_misc_device.rs
+++ b/samples/rust/rust_misc_device.rs
@@ -12,6 +12,7 @@
//! #include <errno.h>
//! #include <fcntl.h>
//! #include <unistd.h>
+//! #include <string.h>
//! #include <sys/ioctl.h>
//!
//! #define RUST_MISC_DEV_FAIL _IO('|', 0)
@@ -19,9 +20,11 @@
//! #define RUST_MISC_DEV_GET_VALUE _IOR('|', 0x81, int)
//! #define RUST_MISC_DEV_SET_VALUE _IOW('|', 0x82, int)
//!
+//! #define BUF_SIZE 16
//! int main() {
//! int value, new_value;
//! int fd, ret;
+//! char *buf[BUF_SIZE];
//!
//! // Open the device file
//! printf("Opening /dev/rust-misc-device for reading and writing\n");
@@ -86,6 +89,40 @@
//! return -1;
//! }
//!
+//! // Write values to the buffer
+//! char *w_buf = "ABCDEFG";
+//! ret = write(fd, w_buf, strlen(w_buf));
+//! if (ret < 0) {
+//! perror("write");
+//! close(fd);
+//! return errno;
+//! }
+//! printf("Write values to the buffer: %.*s\n", ret, w_buf);
+//!
+//! // Read values from the buffer
+//! lseek(fd, 0, SEEK_SET);
+//! ret = read(fd, buf, BUF_SIZE - 1);
+//! if (ret < 0) {
+//! perror("read");
+//! close(fd);
+//! return errno;
+//! }
+//! buf[ret] = '\0';
+//! printf("Read values from the buffer: %s\n", buf);
+//!
+//! // Read value from the middle of the buffer
+//! memset(buf, 0, sizeof(buf));
+//! lseek(fd, 1, SEEK_SET);
+//! lseek(fd, 2, SEEK_CUR);
+//! ret = read(fd, buf, BUF_SIZE - 1);
+//! if (ret < 0) {
+//! perror("read");
+//! close(fd);
+//! return errno;
+//! }
+//! buf[ret] = '\0';
+//! printf("Read values from the middle of the buffer: %s\n", buf);
+//!
//! // Close the device file
//! printf("Closing /dev/rust-misc-device\n");
//! close(fd);
@@ -114,6 +151,9 @@
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;
+
module! {
type: RustMiscDeviceModule,
name: "rust_misc_device",
@@ -204,6 +244,34 @@ fn write_iter(mut kiocb: Kiocb<'_, Self::Ptr>, iov: &mut IovIterSource<'_>) -> R
Ok(len)
}

+ fn llseek(
+ me: Pin<&RustMiscDevice>,
+ file: &mut File,
+ offset: i64,
+ whence: i32,
+ ) -> Result<isize> {
+ dev_info!(me.dev, "LLSEEK Rust Misc Device Sample\n");
+ let pos: i64 = file.pos();
+
+ let new_pos = match whence {
+ SEEK_SET => offset,
+ SEEK_CUR => pos + 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);
+ }
+
+ *file.pos_mut() = new_pos;
+
+ Ok(new_pos as isize)
+ }
+
fn ioctl(me: Pin<&RustMiscDevice>, _file: &File, cmd: u32, arg: usize) -> Result<isize> {
dev_info!(me.dev, "IOCTLing Rust Misc Device Sample\n");

--
2.51.0