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Message-ID: <ZSebS0pQfoF4eTsD@boqun-archlinux> Date: Thu, 12 Oct 2023 00:07:55 -0700 From: Boqun Feng <boqun.feng@...il.com> To: FUJITA Tomonori <fujita.tomonori@...il.com> Cc: netdev@...r.kernel.org, rust-for-linux@...r.kernel.org, andrew@...n.ch, miguel.ojeda.sandonis@...il.com, greg@...ah.com, tmgross@...ch.edu Subject: Re: [PATCH net-next v3 1/3] rust: core abstractions for network PHY drivers On Thu, Oct 12, 2023 at 03:44:44PM +0900, FUJITA Tomonori wrote: > On Wed, 11 Oct 2023 23:34:18 -0700 > Boqun Feng <boqun.feng@...il.com> wrote: > > > On Thu, Oct 12, 2023 at 02:58:24PM +0900, FUJITA Tomonori wrote: > >> On Wed, 11 Oct 2023 11:29:45 -0700 > >> Boqun Feng <boqun.feng@...il.com> wrote: > >> > >> > On Mon, Oct 09, 2023 at 10:39:10AM +0900, FUJITA Tomonori wrote: > >> > [...] > >> >> +impl Device { > >> >> + /// Creates a new [`Device`] instance from a raw pointer. > >> >> + /// > >> >> + /// # Safety > >> >> + /// > >> >> + /// For the duration of the lifetime 'a, the pointer must be valid for writing and nobody else > >> >> + /// may read or write to the `phy_device` object. > >> >> + pub unsafe fn from_raw<'a>(ptr: *mut bindings::phy_device) -> &'a mut Self { > >> >> + unsafe { &mut *ptr.cast() } > >> >> + } > >> >> + > >> >> + /// Gets the id of the PHY. > >> >> + pub fn phy_id(&mut self) -> u32 { > >> > > >> > This function doesn't modify the `self`, why does this need to be a > >> > `&mut self` function? Ditto for a few functions in this impl block. > >> > > >> > It seems you used `&mut self` for all the functions, which looks like > >> > more design work is required here. > >> > >> Ah, I can drop all the mut here. > > > > It may not be that easy... IIUC, most of the functions in the `impl` > > block can only be called correctly with phydev->lock held. In other > > words, their usage requires exclusive accesses. We should somehow > > express this in the type system, otherwise someone may lose track on > > this requirement in the future (for example, calling any function > > without the lock held). > > > > A simple type trick comes to me is that > > > > impl Device { > > // rename `from_raw` into `assume_locked` > > pub unsafe fn assume_locked<'a>(ptr: *mut bindings::phy_device) -> &'a LockedDevice { > > ... > > } > > } > > Hmm, the concept of PHYLIB is that a driver never play with a > lock. From the perspective of PHYLIB, this abstraction is a PHY > driver. The abstraction should not touch the lock. > Well, usually we want to describe such a constrait/requirement in the type system, that's part of the Rust bindings, of course, for some properties it may be hard, so it may be impossible. > How can someone lose track on this requirement? The abstraction > creates a Device instance only inside the callbacks. > Right now, yes. The code in the patch only "creates" a Device inside the callbacks, but the `Device::from_raw` function doesn't mention any of this requirement, if the design is only called inside the callbacks, please add something in the function's `# Safety` requirement, since voliating this may cause memory safety issue. Type system and unsafe comments are contracts, if one API has a limited usage by design, people should be able to find it somewhere in the contracts. Regards, Boqun
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