On Fri, Jul 4, 2025 at 6:09 AM Benno Lossin <los...@kernel.org> wrote: > > On Fri Jul 4, 2025 at 1:23 AM CEST, Tamir Duberstein wrote: > > On Thu, Jul 3, 2025 at 6:41 PM Tamir Duberstein <tam...@gmail.com> wrote: > >> On Thu, Jul 3, 2025 at 4:36 PM Benno Lossin <los...@kernel.org> wrote: > >> > > >> > I don't understand, can't you just do: > >> > > >> > * add `rust/kernel/fmt.rs`, > >> > * add `rust/macros/fmt.rs`, > >> > * change all occurrences of `core::fmt` to `kernel::fmt` and > >> > `format_args!` to `fmt!`. > >> > >> Yes, such a split could be done - I will do so in the next spin > >> > >> > >> > The last one could be split by subsystem, no? Some subsystems might > >> > interact and thus need simultaneous splitting, but there should be some > >> > independent ones. > >> > >> Yes, it probably can. As you say, some subsystems might interact - the > >> claimed benefit of doing this subsystem-by-subsystem split is that it > >> avoids conflicts with ongoing work that will conflict with a large > >> patch, but this is also the downside; if ongoing work changes the set > >> of interactions between subsystems then a maintainer may find > >> themselves unable to emit the log message they want (because one > >> subsystem is using kernel::fmt while another is still on core::fmt). > > > > I gave this a try. I ran into the problem that `format_args!` (and, > > after this patch, `fmt!`) is at the center of `print_macro!`, which > > itself underpins various other formatting macros. This means we'd have > > to bifurcate the formatting infrastructure to support an incremental > > migration. That's quite a bit of code, and likely quite a mess in the > > resulting git history -- and that's setting aside the toil required to > > figure out the correct combinations of subsystems that must migrate > > together. > > So here is what we can do without duplicating the logic, though it > requires multiple cycles: > > 1. We merge the two `fmt.rs` files & each subsystem merges an > implementation of `kernel::fmt::Display` for their types, but keeps > the `core::fmt::Display` impl around. > 2. After all subsystems have merged the previous step, we change the > implementations of `print_macro!` to use `fmt!` instead of > `format_args!`. > 3. We remove all occurrences of `core::fmt` (& replace them with > `kernel::fmt`), removing the `core::fmt::Display` impls.
That would probably work. We will probably see regressions because we can't just replace `core::fmt` imports with `kernel::fmt`, so new code may appear that uses the former. I think this discussion would be productive on the next spin. The changes in other subsystems are now almost entirely changing of import paths -- perhaps that would be sufficiently uncontroversial for folks to give their Acked-bys.
