Re: [PATCH 1/2] samples: rust: Provide example using the new Rust MiscDevice abstraction

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Dec 05, 2024 at 09:17:04AM +0000, Lee Jones wrote:
> On Thu, 05 Dec 2024, Greg KH wrote:
> 
> > On Thu, Dec 05, 2024 at 08:41:01AM +0000, Lee Jones wrote:
> > > On Wed, 04 Dec 2024, Greg KH wrote:
> > > 
> > > > On Wed, Dec 04, 2024 at 05:46:24PM +0000, Lee Jones wrote:
> > > > > This sample driver demonstrates the following basic operations:
> > > > > 
> > > > > * Register a Misc Device
> > > > > * Create /dev/rust-misc-device
> > > > > * Open the aforementioned character device
> > > > > * Operate on the character device via a simple ioctl()
> > > > > * Close the character device
> > > > > 
> > > > > Signed-off-by: Lee Jones <lee@kernel.org>
> > > > > ---
> > > > >  samples/rust/Kconfig             | 10 ++++
> > > > >  samples/rust/Makefile            |  1 +
> > > > >  samples/rust/rust_misc_device.rs | 84 ++++++++++++++++++++++++++++++++
> > > > >  3 files changed, 95 insertions(+)
> > > > >  create mode 100644 samples/rust/rust_misc_device.rs
> > > > > 
> > > > > diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
> > > > > index b0f74a81c8f9..df384e679901 100644
> > > > > --- a/samples/rust/Kconfig
> > > > > +++ b/samples/rust/Kconfig
> > > > > @@ -20,6 +20,16 @@ config SAMPLE_RUST_MINIMAL
> > > > >  
> > > > >  	  If unsure, say N.
> > > > >  
> > > > > +config SAMPLE_RUST_MISC_DEVICE
> > > > > +	tristate "Misc device"
> > > > > +	help
> > > > > +	  This option builds the Rust misc device.
> > > > > +
> > > > > +	  To compile this as a module, choose M here:
> > > > > +	  the module will be called rust_misc_device.
> > > > > +
> > > > > +	  If unsure, say N.
> > > > > +
> > > > >  config SAMPLE_RUST_PRINT
> > > > >  	tristate "Printing macros"
> > > > >  	help
> > > > > diff --git a/samples/rust/Makefile b/samples/rust/Makefile
> > > > > index c1a5c1655395..ad4b97a98580 100644
> > > > > --- a/samples/rust/Makefile
> > > > > +++ b/samples/rust/Makefile
> > > > > @@ -2,6 +2,7 @@
> > > > >  ccflags-y += -I$(src)				# needed for trace events
> > > > >  
> > > > >  obj-$(CONFIG_SAMPLE_RUST_MINIMAL)		+= rust_minimal.o
> > > > > +obj-$(CONFIG_SAMPLE_RUST_MISC_DEVICE)		+= rust_misc_device.o
> > > > >  obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
> > > > >  
> > > > >  rust_print-y := rust_print_main.o rust_print_events.o
> > > > > diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
> > > > > new file mode 100644
> > > > > index 000000000000..5f1b69569ef7
> > > > > --- /dev/null
> > > > > +++ b/samples/rust/rust_misc_device.rs
> > > > > @@ -0,0 +1,84 @@
> > > > > +// SPDX-License-Identifier: GPL-2.0
> > > > 
> > > > Nit, you forgot a copyright line here :)
> > > 
> > > I can add one, but none of the other drivers in this directory has one.
> > 
> > I think the copyright owner of this file will appreciate that.  In fact,
> > I think it might be required by them :)
> 
> I think you're right.  Probably just an oversight from the original.
> 
> > > > Anyway, other than the copyright, this looks good to me.
> > > > 
> > > > Although we should get the "validate the data" rust patch set in here
> > > > soon, so we don't have to go and fix up all users of the miscdev rust
> > > > api at once.  Maybe I'll dig that series up over the holiday break if
> > > > someone doesn't beat me to it.
> > > 
> > > What needs doing?  Do you have a link?
> > 
> > https://lore.kernel.org/r/20240925205244.873020-1-benno.lossin@proton.me
> > 
> > But in thinking about it more, this isn't going to work well with misc
> > devices as the data is coming from userspace, which already goes through
> > the user slice code.  Unless userslice should be marking the data as
> > untrusted?  I think that needs to happen as well.
> 
> Not too relevant here I think.  The data coming in is just a single int
> that is used as-is rather than any kind of index into memory.

For now, yes.  But in reality, the data is "untrusted" as userspace
provided it, and for a sample, we should at least document that
otherwise people will forget.

thanks,

greg k-h