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Message-ID: <20241205083848.GD7451@google.com>
Date: Thu, 5 Dec 2024 08:38:48 +0000
From: Lee Jones <lee@...nel.org>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, ojeda@...nel.org, alex.gaynor@...il.com,
boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com,
benno.lossin@...ton.me, a.hindborg@...nel.org, aliceryhl@...gle.com,
tmgross@...ch.edu, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 2/2] sample: rust_misc_device: Demonstrate additional
get/set value functionality
On Wed, 04 Dec 2024, Greg KH wrote:
> On Wed, Dec 04, 2024 at 05:46:25PM +0000, Lee Jones wrote:
> > Expand the complexity of the sample driver by providing the ability to
> > get and set an integer. The value is protected by a mutex.
> >
> > Here is a simple userspace program that fully exercises the sample
> > driver's capabilities.
> >
> > int main() {
> > int value, new_value;
> > int fd, ret;
> >
> > // Open the device file
> > printf("Opening /dev/rust-misc-device for reading and writing\n");
> > fd = open("/dev/rust-misc-device", O_RDWR);
> > if (fd < 0) {
> > perror("open");
> > return errno;
> > }
> >
> > // Make call into driver to say "hello"
> > printf("Calling Hello\n");
> > ret = ioctl(fd, RUST_MISC_DEV_HELLO, NULL);
> > if (ret < 0) {
> > perror("ioctl: Failed to call into Hello");
> > close(fd);
> > return errno;
> > }
> >
> > // Get initial value
> > printf("Fetching initial value\n");
> > ret = ioctl(fd, RUST_MISC_DEV_GET_VALUE, &value);
> > if (ret < 0) {
> > perror("ioctl: Failed to fetch the initial value");
> > close(fd);
> > return errno;
> > }
> >
> > value++;
> >
> > // Set value to something different
> > printf("Submitting new value (%d)\n", value);
> > ret = ioctl(fd, RUST_MISC_DEV_SET_VALUE, &value);
> > if (ret < 0) {
> > perror("ioctl: Failed to submit new value");
> > close(fd);
> > return errno;
> > }
> >
> > // Ensure new value was applied
> > printf("Fetching new value\n");
> > ret = ioctl(fd, RUST_MISC_DEV_GET_VALUE, &new_value);
> > if (ret < 0) {
> > perror("ioctl: Failed to fetch the new value");
> > close(fd);
> > return errno;
> > }
> >
> > if (value != new_value) {
> > printf("Failed: Committed and retrieved values are different (%d - %d)\n", value, new_value);
> > close(fd);
> > return -1;
> > }
> >
> > // Call the unsuccessful ioctl
> > printf("Attempting to call in to an non-existent IOCTL\n");
> > ret = ioctl(fd, RUST_MISC_DEV_FAIL, NULL);
> > if (ret < 0) {
> > perror("ioctl: Succeeded to fail - this was expected");
> > } else {
> > printf("ioctl: Failed to fail\n");
> > close(fd);
> > return -1;
> > }
> >
> > // Close the device file
> > printf("Closing /dev/rust-misc-device\n");
> > close(fd);
> >
> > printf("Success\n");
> > return 0;
> > }
> >
> > Signed-off-by: Lee Jones <lee@...nel.org>
> > ---
> > samples/rust/rust_misc_device.rs | 82 ++++++++++++++++++++++++--------
> > 1 file changed, 62 insertions(+), 20 deletions(-)
> >
> > diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
> > index 5f1b69569ef7..9c041497d881 100644
> > --- a/samples/rust/rust_misc_device.rs
> > +++ b/samples/rust/rust_misc_device.rs
> > @@ -2,13 +2,20 @@
> >
> > //! Rust misc device sample.
> >
> > +use core::pin::Pin;
> > +
> > use kernel::{
> > c_str,
> > - ioctl::_IO,
> > + ioctl::{_IO, _IOC_SIZE, _IOR, _IOW},
> > miscdevice::{MiscDevice, MiscDeviceOptions, MiscDeviceRegistration},
> > + new_mutex,
> > prelude::*,
> > + sync::Mutex,
> > + uaccess::{UserSlice, UserSliceReader, UserSliceWriter},
> > };
> >
> > +const RUST_MISC_DEV_GET_VALUE: u32 = _IOR::<i32>('R' as u32, 7);
> > +const RUST_MISC_DEV_SET_VALUE: u32 = _IOW::<i32>('R' as u32, 8);
>
> Shouldn't this be 'W'?
No, I don't think so.
'W' doesn't mean 'write'. It's supposed to be a unique identifier:
'W' 00-1F linux/watchdog.h conflict!
'W' 00-1F linux/wanrouter.h conflict! (pre 3.9)
'W' 00-3F sound/asound.h conflict!
'W' 40-5F drivers/pci/switch/switchtec.c
'W' 60-61 linux/watch_queue.h
'R' isn't registered for this either:
'R' 00-1F linux/random.h conflict!
'R' 01 linux/rfkill.h conflict!
'R' 20-2F linux/trace_mmap.h
'R' C0-DF net/bluetooth/rfcomm.h
'R' E0 uapi/linux/fsl_mc.h
... but since this is just example code with no real purpose, I'm going
to hold short of registering a unique identifier for it.
> > const RUST_MISC_DEV_HELLO: u32 = _IO('R' as u32, 9);
> >
> > module! {
> > @@ -40,45 +47,80 @@ fn init(_module: &'static ThisModule) -> Result<Self> {
> > }
> > }
> >
> > -struct RustMiscDevice;
> > +struct Inner {
> > + value: i32,
> > +}
> >
> > -impl RustMiscDevice {
> > - fn new() -> Self {
> > - Self
> > - }
> > +#[pin_data(PinnedDrop)]
> > +struct RustMiscDevice {
> > + #[pin]
> > + inner: Mutex<Inner>,
> > }
> >
> > #[vtable]
> > impl MiscDevice for RustMiscDevice {
> > - type Ptr = KBox<Self>;
> > + type Ptr = Pin<KBox<Self>>;
> >
> > - fn open() -> Result<KBox<Self>> {
> > + fn open() -> Result<Pin<KBox<Self>>> {
> > pr_info!("Opening Rust Misc Device Sample\n");
> >
> > - Ok(KBox::new(RustMiscDevice::new(), GFP_KERNEL)?)
> > + KBox::try_pin_init(
> > + try_pin_init! {
> > + RustMiscDevice { inner <- new_mutex!( Inner{ value: 0_i32 } )}
> > + },
> > + GFP_KERNEL,
> > + )
> > }
> >
> > - fn ioctl(
> > - _device: <Self::Ptr as kernel::types::ForeignOwnable>::Borrowed<'_>,
> > - cmd: u32,
> > - _arg: usize,
> > - ) -> Result<isize> {
> > + fn ioctl(device: Pin<&RustMiscDevice>, cmd: u32, arg: usize) -> Result<isize> {
> > pr_info!("IOCTLing Rust Misc Device Sample\n");
> >
> > - match cmd {
> > - RUST_MISC_DEV_HELLO => pr_info!("Hello from the Rust Misc Device\n"),
> > + let size = _IOC_SIZE(cmd);
> > +
> > + let _ = match cmd {
> > + RUST_MISC_DEV_GET_VALUE => device.get_value(UserSlice::new(arg, size).writer())?,
> > + RUST_MISC_DEV_SET_VALUE => device.set_value(UserSlice::new(arg, size).reader())?,
> > + RUST_MISC_DEV_HELLO => device.hello()?,
> > _ => {
> > - pr_err!("IOCTL not recognised: {}\n", cmd);
> > + pr_err!("-> IOCTL not recognised: {}\n", cmd);
> > return Err(EINVAL);
>
> Nit, wrong return value for an invalid ioctl, I missed that in patch 1,
> sorry about that.
Good shout, thanks.
> > }
> > - }
> > + };
> >
> > Ok(0)
> > }
> > }
> >
> > -impl Drop for RustMiscDevice {
> > - fn drop(&mut self) {
> > +#[pinned_drop]
> > +impl PinnedDrop for RustMiscDevice {
> > + fn drop(self: Pin<&mut Self>) {
> > pr_info!("Exiting the Rust Misc Device Sample\n");
> > }
> > }
> > +
> > +impl RustMiscDevice {
> > + fn set_value(&self, mut reader: UserSliceReader) -> Result<isize> {
> > + let new_value = reader.read::<i32>()?;
> > + let mut guard = self.inner.lock();
> > +
> > + pr_info!("-> Copying data from userspace (value: {})\n", new_value);
> > +
> > + guard.value = new_value;
> > + Ok(0)
> > + }
> > +
> > + fn get_value(&self, mut writer: UserSliceWriter) -> Result<isize> {
> > + let guard = self.inner.lock();
> > +
> > + pr_info!("-> Copying data to userspace (value: {})\n", &guard.value);
> > +
> > + writer.write::<i32>(&guard.value)?;
>
> What happens if it fails, shouldn't your pr_info() happen after this?
If this fails, I need the line in the log to show where it failed.
It says "copying" as in "attempting to copy", rather than "copied".
--
Lee Jones [李琼斯]
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