On Tue, 20 Oct 2026 23:36:56 +0200
Thomas Weißschuh <[email protected]> wrote:
> On 2026-10-20 21:25:42+0300, Zhi Wang wrote:
> > On Tue, 20 Oct 2026 19:30:33 +0200
> > Thomas Weißschuh <[email protected]> wrote:
> >
> > > +To: Zhi Wang
> > >
> >
> > Thanks Alex for bridge the threads together!
> >
> > Hey Thomas,
> >
> > Thanks for the comparison! As a user of this feature, I'm happy to
> > combine the two series and see this making progress.
> >
> > The Bounded types, bitfield tests, and module_path!() fallback look
> > like useful additions. One clarification: with CONFIG_JUMP_LABEL,
> > our disabled path already has no FFI call.
> > static_branch_unlikely!() is sufficient for our initially disabled
> > callsites, including enabling them at runtime.
>
> Ack. Although adding jump label support as a later step would make the
> patches smaller and easier to review.
>
> > For the combined series, I'd like to retain these behaviors:
> >
> > - Debug logging is independent of debug_assertions, starts disabled,
> > and is controlled through dynamic debug. IMHO, fewer distro
> > kernels are compiled with CONFIG_RUST_DEBUG_ASSERTIONS=y nowadays.
> > (At least, Arch and Fedora are compiled with N)
>
> Ack. It would still be useful to also support default-enabled
> callsites, like the C version does. What about '--cfg DEBUG'?
>
Agree.
> > - Disabled pr_debug!()/dev_dbg!() calls do not evaluate their
> > arguments. IMHO, it seems the current dev_dbg!() in your patch
> > evaluates the params before checking the switch on/off.
> > (pr_debug()! looks fine though)
>
> As far as I understand, fmt!() itself does not yet evaluate the
> expressions passed as arguments. It only typechecks and
> creates the precompiled Arguments<'_> structure. The parameters'
> Display traits are only executed when the Arguments<'_> is written
> somewhere. IMO the typechecking should be done even if the code is
> going to be compiled out. Similar to no_printk() on the C side.
>
I encountered this problem by chance while developing my patches and
testing it on nova-core (unexpected evaluation of a register operation
while dynamic debug is off). IMHO, it seems constructing Arguments
evaluates the expressions immediately even if the resulting arguments
are never formatted.
I made a test on top of your WIP branch, the example is:
pr_debug!("dyndbg repro pr: {}\n", read_status(&reads, &formats));
dev_dbg!(fdev, dyndbg repro dev: {}\n", read_status(&reads, &formats));
reads and formats are two counters.
With dynamic debug disabled, both macros produce:
dyndbg repro pr: args=1 fmt=0
dyndbg repro dev: args=1 fmt=0
which shows the params are evaluated unexpectedly.
My solution was moving the fmt!() into dynamic_func_call()!
I attached the testing code as well. Feel free to try it.
> > - The dynamic-debug prefix flags remain supported. (I use the C
> > version of dynamic debug to support e.g. +m, +l and _t)
>
> Absolutely, this is a bug in my v1. It is fixed in v2.
>
> > Could you share your pending encapsulation/Opaque and static-branch
> > wip patches? We can then work out how they fit together, incorporate
> > Alice's review feedback, and preserve attribution for Andrew's work.
>
> Here:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/thomas.weissschuh/linux.git/log/?h=b4/rust-dyndbg
>
> > Thanks,
> > Zhi.
> >
> > > Hi Alexandre,
> > >
> > > On 2026-10-20 22:14:12+0900, Alexandre Courbot wrote:
> > > > On Sun Oct 11, 2026 at 9:52 PM JST, Thomas Weißschuh wrote:
> > > > > Add the Rust infrastructure to integrate with the dynamic
> > > > > debug infrastructure.
> > > > >
> > > > > Static keys are not used for now, as the full bindings are
> > > > > missing for those. A follow-up series will add that.
> > > > > Also custom classes are not supported yet, but could be added
> > > > > on top.
> > > > >
> > > > > Patches 1-4: Generic Rust preparation patches.
> > > > > Patches 5-7: C dynamic debug preparation patches.
> > > > > Patches 8: Rust Dynamic debug infrastructure.
> > > > > Patches 9-11: Rust Dynamic debug enablement.
> > > >
> > > > Were you aware of this series [1]?
> > >
> > > I was was told about the original work from Andrew back at
> > > Kangrejos. However I was unable to find it on LKML and it was not
> > > clear how far along that series has come along. The posting of
> > > Zhi's v3 only happened after I started on my variant, and I did
> > > not see it until you mentioned it. So my development is
> > > completely independent from Andrew's and Zhi's.
> > >
> > > > There seems to be quite a bit of overlap.
> > >
> > > Indeed. I see pros for both serieses:
> > >
> > > Mine:
> > > * No FFI in the fastpath.
> > > * No need for RUST_MODNAME.
> > > * Use of Bounded.
> > > * Tests for the flag encoding.
> > > * modname!() as function name.
> > > (As discussed with Benno and Gary and LPC)
> > > * Better encapsulation of 'struct Descriptor' (partially not yet
> > > posted)
> > > * Use of Opaque<> to wrap bindings::_ddebug (not yet posted).
> > > * Use of !cv() (not yet posted).
> > >
> > > Andrew/Zhi:
> > > * Better docs.
> > > * Static branch support.
> > > * static_branch_likely!() support is missing however.
> > > * I also have follow-up patches to enable
> > > static_branch_likely!().
> > > * host doctest support.
> > >
> > > I am perfectly fine with merging both serieses.
> > >
> > >
> > > Thomas
> > >
> > > > [1]
> > > > https://lore.kernel.org/all/[email protected]/
> > > >
> >
>
diff --git a/samples/rust/rust_driver_faux.rs b/samples/rust/rust_driver_faux.rs
index de131fce491a..6db3124ed3a9 100644
--- a/samples/rust/rust_driver_faux.rs
+++ b/samples/rust/rust_driver_faux.rs
@@ -2,8 +2,10 @@
//! Rust faux device sample.
+use core::cell::Cell;
use kernel::{
faux,
+ fmt,
prelude::*,
Module, //
};
@@ -20,6 +22,20 @@ struct SampleModule {
_reg: faux::Registration,
}
+struct Status<'a>(&'a Cell<usize>);
+
+impl fmt::Display for Status<'_> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ self.0.set(self.0.get() + 1);
+ f.write_str("ready")
+ }
+}
+
+fn read_status<'a>(reads: &Cell<usize>, formats: &'a Cell<usize>) -> Status<'a> {
+ reads.set(reads.get() + 1);
+ Status(formats)
+}
+
impl Module for SampleModule {
fn init(_module: &'static ThisModule) -> Result<Self> {
pr_info!("Initialising Rust Faux Device Sample\n");
@@ -30,6 +46,28 @@ fn init(_module: &'static ThisModule) -> Result<Self> {
dev_info!(fdev, "Hello from faux device!\n");
dev_dbg!(fdev, "foobar\n");
+ let reads = Cell::new(0);
+ let formats = Cell::new(0);
+ pr_debug!("dyndbg repro pr: {}\n", read_status(&reads, &formats));
+ pr_info!(
+ "dyndbg repro pr: args={} fmt={}\n",
+ reads.get(),
+ formats.get()
+ );
+
+ reads.set(0);
+ formats.set(0);
+ dev_dbg!(
+ fdev,
+ "dyndbg repro dev: {}\n",
+ read_status(&reads, &formats)
+ );
+ pr_info!(
+ "dyndbg repro dev: args={} fmt={}\n",
+ reads.get(),
+ formats.get()
+ );
+
Ok(Self { _reg: reg })
}
}
--
2.53.0
