* Re: [PATCH] rust: kernel: drop repetition in offset_of macro
2022-12-16 18:26 ` Wedson Almeida Filho
@ 2022-12-16 22:15 ` Boqun Feng
2022-12-16 23:30 ` Wei Liu
2022-12-16 23:08 ` Wei Liu
2022-12-16 23:15 ` Wei Liu
2 siblings, 1 reply; 7+ messages in thread
From: Boqun Feng @ 2022-12-16 22:15 UTC (permalink / raw)
To: Wedson Almeida Filho
Cc: Wei Liu, rust-for-linux, Linux Kernel List, Miguel Ojeda,
Alex Gaynor, Gary Guo, Björn Roy Baron
On Fri, Dec 16, 2022 at 06:26:57PM +0000, Wedson Almeida Filho wrote:
> On Fri, 16 Dec 2022 at 17:49, Wei Liu <wei.liu@kernel.org> wrote:
> >
> > It doesn't make sense to allow multiple fields to be specified in
> > offset_of.
>
> Why do you say it doesn't make sense?
>
> Here's what I had in mind:
> ```
> struct Y {
> z: u32
> }
> struct X {
> y: Y
> }
> offset_of!(X, y.z)
For me, it's not very obvious that "y.z" is multiples of token trees
rather a single token tree ;-)
Maybe some examples of the match pattern of macros can help people catch
up faster? Like
"y.z" => tt [y], tt [.], tt [z]
I will defer to Gary or Bjorn for a better quick guide of Rust macros
;-)
Regards,
Boqun
> ```
>
> Which is something very plausible.
>
> > No functional change.
> >
> > Signed-off-by: Wei Liu <wei.liu@kernel.org>
> > ---
> > Cc: Miguel Ojeda <ojeda@kernel.org>
> > Cc: Alex Gaynor <alex.gaynor@gmail.com>
> > Cc: Wedson Almeida Filho <wedsonaf@gmail.com>
> > Cc: Boqun Feng <boqun.feng@gmail.com>
> > Cc: Gary Guo <gary@garyguo.net>
> > Cc: Björn Roy Baron <bjorn3_gh@protonmail.com>
> > ---
> > rust/kernel/lib.rs | 10 ++++++----
> > 1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> > index 6a322effa60c..2f3601e4e27e 100644
> > --- a/rust/kernel/lib.rs
> > +++ b/rust/kernel/lib.rs
> > @@ -208,7 +208,7 @@ impl<'a> Drop for KParamGuard<'a> {
> > /// ```
> > #[macro_export]
> > macro_rules! offset_of {
> > - ($type:ty, $($f:tt)*) => {{
> > + ($type:ty, $f:tt) => {{
> > let tmp = core::mem::MaybeUninit::<$type>::uninit();
> > let outer = tmp.as_ptr();
> > // To avoid warnings when nesting `unsafe` blocks.
> > @@ -216,12 +216,14 @@ macro_rules! offset_of {
> > // SAFETY: The pointer is valid and aligned, just not initialised; `addr_of` ensures that
> > // we don't actually read from `outer` (which would be UB) nor create an intermediate
> > // reference.
> > - let inner = unsafe { core::ptr::addr_of!((*outer).$($f)*) } as *const u8;
> > + let inner = unsafe { core::ptr::addr_of!((*outer).$f) } as *const u8;
> > // To avoid warnings when nesting `unsafe` blocks.
> > #[allow(unused_unsafe)]
> > // SAFETY: The two pointers are within the same allocation block.
> > - unsafe { inner.offset_from(outer as *const u8) }
> > - }}
> > + unsafe {
> > + inner.offset_from(outer as *const u8)
> > + }
> > + }};
> > }
> >
> > /// Produces a pointer to an object from a pointer to one of its fields.
> > --
> > 2.35.1
> >
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] rust: kernel: drop repetition in offset_of macro
2022-12-16 22:15 ` Boqun Feng
@ 2022-12-16 23:30 ` Wei Liu
2022-12-16 23:57 ` Miguel Ojeda
0 siblings, 1 reply; 7+ messages in thread
From: Wei Liu @ 2022-12-16 23:30 UTC (permalink / raw)
To: Boqun Feng
Cc: Wedson Almeida Filho, Wei Liu, rust-for-linux, Linux Kernel List,
Miguel Ojeda, Alex Gaynor, Gary Guo, Björn Roy Baron
On Fri, Dec 16, 2022 at 02:15:16PM -0800, Boqun Feng wrote:
> On Fri, Dec 16, 2022 at 06:26:57PM +0000, Wedson Almeida Filho wrote:
> > On Fri, 16 Dec 2022 at 17:49, Wei Liu <wei.liu@kernel.org> wrote:
> > >
> > > It doesn't make sense to allow multiple fields to be specified in
> > > offset_of.
> >
> > Why do you say it doesn't make sense?
> >
> > Here's what I had in mind:
> > ```
> > struct Y {
> > z: u32
> > }
> > struct X {
> > y: Y
> > }
> > offset_of!(X, y.z)
>
> For me, it's not very obvious that "y.z" is multiples of token trees
> rather a single token tree ;-)
>
> Maybe some examples of the match pattern of macros can help people catch
> up faster? Like
>
> "y.z" => tt [y], tt [.], tt [z]
>
> I will defer to Gary or Bjorn for a better quick guide of Rust macros
> ;-)
>
What will be even better is someone please contribute such a macro to
libcore so that I don't have to replicate the code snippet everywhere.
:-)
I have a version somewhere, the second argument matches against ident,
which was definitely not as flexible as tt.
Thanks,
Wei.
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] rust: kernel: drop repetition in offset_of macro
2022-12-16 23:30 ` Wei Liu
@ 2022-12-16 23:57 ` Miguel Ojeda
0 siblings, 0 replies; 7+ messages in thread
From: Miguel Ojeda @ 2022-12-16 23:57 UTC (permalink / raw)
To: Wei Liu
Cc: Boqun Feng, Wedson Almeida Filho, rust-for-linux,
Linux Kernel List, Miguel Ojeda, Alex Gaynor, Gary Guo,
Björn Roy Baron
On Sat, Dec 17, 2022 at 12:30 AM Wei Liu <wei.liu@kernel.org> wrote:
>
> What will be even better is someone please contribute such a macro to
> libcore so that I don't have to replicate the code snippet everywhere.
> :-)
It is happening! :-) See https://github.com/rust-lang/rfcs/pull/3308,
currently at the end of the FCP ("final comment period"), i.e. the RFC
is likely getting accepted soon.
We track it at https://github.com/Rust-for-Linux/linux/issues/514 (one
of the sub-lists in issue #2).
Cheers,
Miguel
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] rust: kernel: drop repetition in offset_of macro
2022-12-16 18:26 ` Wedson Almeida Filho
2022-12-16 22:15 ` Boqun Feng
@ 2022-12-16 23:08 ` Wei Liu
2022-12-16 23:15 ` Wei Liu
2 siblings, 0 replies; 7+ messages in thread
From: Wei Liu @ 2022-12-16 23:08 UTC (permalink / raw)
To: Wedson Almeida Filho
Cc: Wei Liu, rust-for-linux, Linux Kernel List, Miguel Ojeda,
Alex Gaynor, Boqun Feng, Gary Guo, Björn Roy Baron
On Fri, Dec 16, 2022 at 06:26:57PM +0000, Wedson Almeida Filho wrote:
> On Fri, 16 Dec 2022 at 17:49, Wei Liu <wei.liu@kernel.org> wrote:
> >
> > It doesn't make sense to allow multiple fields to be specified in
> > offset_of.
>
> Why do you say it doesn't make sense?
>
> Here's what I had in mind:
> ```
> struct Y {
> z: u32
> }
> struct X {
> y: Y
> }
> offset_of!(X, y.z)
> ```
>
> Which is something very plausible.
You're right. I didn't consider that use case. This patch can be
ignored.
Thanks,
Wei.
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] rust: kernel: drop repetition in offset_of macro
2022-12-16 18:26 ` Wedson Almeida Filho
2022-12-16 22:15 ` Boqun Feng
2022-12-16 23:08 ` Wei Liu
@ 2022-12-16 23:15 ` Wei Liu
2 siblings, 0 replies; 7+ messages in thread
From: Wei Liu @ 2022-12-16 23:15 UTC (permalink / raw)
To: Wedson Almeida Filho
Cc: Wei Liu, rust-for-linux, Linux Kernel List, Miguel Ojeda,
Alex Gaynor, Boqun Feng, Gary Guo, Björn Roy Baron
On Fri, Dec 16, 2022 at 06:26:57PM +0000, Wedson Almeida Filho wrote:
> On Fri, 16 Dec 2022 at 17:49, Wei Liu <wei.liu@kernel.org> wrote:
> >
> > It doesn't make sense to allow multiple fields to be specified in
> > offset_of.
>
> Why do you say it doesn't make sense?
>
> Here's what I had in mind:
> ```
> struct Y {
> z: u32
> }
> struct X {
> y: Y
> }
> offset_of!(X, y.z)
> ```
>
> Which is something very plausible.
>
> > No functional change.
> >
> > Signed-off-by: Wei Liu <wei.liu@kernel.org>
> > ---
> > Cc: Miguel Ojeda <ojeda@kernel.org>
> > Cc: Alex Gaynor <alex.gaynor@gmail.com>
> > Cc: Wedson Almeida Filho <wedsonaf@gmail.com>
> > Cc: Boqun Feng <boqun.feng@gmail.com>
> > Cc: Gary Guo <gary@garyguo.net>
> > Cc: Björn Roy Baron <bjorn3_gh@protonmail.com>
> > ---
> > rust/kernel/lib.rs | 10 ++++++----
> > 1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> > index 6a322effa60c..2f3601e4e27e 100644
> > --- a/rust/kernel/lib.rs
> > +++ b/rust/kernel/lib.rs
> > @@ -208,7 +208,7 @@ impl<'a> Drop for KParamGuard<'a> {
> > /// ```
> > #[macro_export]
> > macro_rules! offset_of {
> > - ($type:ty, $($f:tt)*) => {{
Shouldn't this be + instead of *?
offset_of!(X,) is valid according to this pattern.
Thanks,
Wei.
^ permalink raw reply [flat|nested] 7+ messages in thread