netdev - Re: [PATCH net-next v7 2/5] rust: net::phy add module_phy

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Date: Sun, 19 Nov 2023 16:50:34 +0100
From: Andrew Lunn <andrew@...n.ch>
To: FUJITA Tomonori <fujita.tomonori@...il.com>
Cc: benno.lossin@...ton.me, boqun.feng@...il.com, netdev@...r.kernel.org,
	rust-for-linux@...r.kernel.org, tmgross@...ch.edu,
	miguel.ojeda.sandonis@...il.com, wedsonaf@...il.com
Subject: Re: [PATCH net-next v7 2/5] rust: net::phy add module_phy_driver
 macro

On Sun, Nov 19, 2023 at 06:25:44PM +0900, FUJITA Tomonori wrote:
> On Fri, 17 Nov 2023 23:01:58 +0000
> Benno Lossin <benno.lossin@...ton.me> wrote:
> 
> > On 11/17/23 23:54, Andrew Lunn wrote:
> >> Each kernel module should be in its own symbol name space. The only
> >> symbols which are visible outside of the module are those exported
> >> using EXPORT_SYMBOL_GPL() or EXPORT_SYMBOL(). A PHY driver does not
> >> export anything, in general.
> >> 
> >> Being built in also does not change this.
> >> 
> >> Neither drivers/net/phy/ax88796b_rust.o nor
> >> rust/doctests_kernel_generated.o should have exported this symbol.
> >> 
> >> I've no idea how this actually works, i guess there are multiple
> >> passes through the linker? Maybe once to resolve symbols across object
> >> files within a module. Normal global symbols are then made local,
> >> leaving only those exported with EXPORT_SYMBOL_GPL() or
> >> EXPORT_SYMBOL()? A second pass through linker then links all the
> >> exported symbols thorough the kernel?
> > 
> > I brought this issue up in [1], but I was a bit confused by your last
> > reply there, as I have no idea how the `EXPORT_SYMBOL` macros work.
> > 
> > IIRC on the Rust side all public items are automatically GPL exported.
> 
> Hmm, they are public but doesn't look like exported by EXPORT_SYMBOL()
> or EXPORT_SYMBOL_GPL().

Do they need to be public? Generally, a PHY driver does not export
anything. So you can probably make them private. We just however need
to ensure the compiler/linker does not think they are unused, so
throws them away.

I would however like to get an understanding how EXPORT_SYMBOL* is
supposed to work in rust. Can it really be hidden away? Or should
methods be explicitly marked like C code? What is the Rust equivalent
of the three levels of symbol scope we have in C?

	Andrew