Re: [RFC PATCH 1/8] rust: kernel: add basic abstractions for device-mapper

[Qingsong Chen]

On 7/14/23 11:48 PM, Benno Lossin wrote:
> > - Declare `vtable` for basic target operations.
> > - Wrap `target_type` to register/unregister target.
> > - Wrap `dm_target`/`dm_dev` to handle io request.
> > - Add a dummy `bio` wrapper.
> >
> > Signed-off-by: Qingsong Chen <changxian.cqs@xxxxxxxxxxxx>
>
> On my system this patch series (I did not test which patch exactly) does
> not compile.
>
> I have left some comments below, they show some patterns present in
> the other patches as well.

Thanks for the comments. Maybe `CONFIG_BLK_DEV_ZONED=y` is needed to
compile this patchset. This is because I cannot define two functions
with the same name in a trait (using the `vtable` macro), just like
the C definition:
```c
#ifdef CONFIG_BLK_DEV_ZONED
typedef int (*dm_report_zones_fn) (struct dm_target *ti,
                                    struct dm_report_zones_args *args,
                                    unsigned int nr_zones);
#else
typedef int (*dm_report_zones_fn) (struct dm_target *dummy);
#endif
```
To fix the `vtable`, I send a little patch[1] the other day. Based on
that, the compile error of this patchset should be fixed too.

[1]:
https://lore.kernel.org/rust-for-linux/20230626074242.3945398-1-changxian.cqs@xxxxxxxxxxxx/

> > +/// The return values of target map function, i.e., [`TargetOperations::map`].
> > +#[repr(u32)]
> > +pub enum MapState {
> > +    /// The target will handle the io by resubmitting it later.
> > +    Submitted = bindings::DM_MAPIO_SUBMITTED,
> > +
> > +    /// Simple remap complete.
> > +    Remapped = bindings::DM_MAPIO_REMAPPED,
> > +
> > +    /// The target wants to requeue the io.
> > +    Requeue = bindings::DM_MAPIO_REQUEUE,
> > +
> > +    /// The target wants to requeue the io after a delay.
> > +    DelayRequeue = bindings::DM_MAPIO_DELAY_REQUEUE,
> > +
> > +    /// The target wants to complete the io.
> > +    Kill = bindings::DM_MAPIO_KILL,
> > +}
>
> Is it really necessary to have these correspond to the exact values?
> Could we also just have a conversion function and leave the repr to
> the compiler?

Sure, we can have a conversion function to return its value to C side
(without `as _`).

Regards,
Qingsong