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AJvYcCWU4H1bG/ZKMsUGAnpgzzA3VB7dGR7+RMN5bPHIbvvRh8QhAYat2uhlrhb+oVr8rL587Mc1WlN+LoBWQ9LIQZmZ/00= X-Gm-Message-State: AOJu0YyuWZ3q2O0cgNpCDR8fVM0nCn3dndfyhiVRDoKFI14pO40bNm/9 ZIBarNmre2kV5u5n22LQXp3NgRhfxQmqK/Jky9Z+geuHwmDSG2erpEwujasBfwApmg9tz9owXEf LAqy2eBNpVxMGEn7JYoGAn3B+6BOqgWoThl0H X-Google-Smtp-Source: AGHT+IH0DKRMGpWhTdEr+rzxMTKBlJSpQK2F/2LMQbeMHgE0zIl7LV+JvtbFFFJCC7Ib7AhMBAhLQOsWxxgbuG3YEis= X-Received: by 2002:a5d:5f45:0:b0:368:3b1f:fe40 with SMTP id ffacd0b85a97d-36baacd2ef4mr2084012f8f.20.1722516544235; Thu, 01 Aug 2024 05:49:04 -0700 (PDT) MIME-Version: 1.0 References: <20240801000641.1882-1-dakr@kernel.org> <20240801000641.1882-10-dakr@kernel.org> In-Reply-To: From: Alice Ryhl Date: Thu, 1 Aug 2024 14:48:52 +0200 Message-ID: Subject: Re: [PATCH v3 09/25] rust: alloc: implement kernel `Box` To: Danilo Krummrich Cc: ojeda@kernel.org, alex.gaynor@gmail.com, wedsonaf@gmail.com, boqun.feng@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, benno.lossin@proton.me, a.hindborg@samsung.com, akpm@linux-foundation.org, daniel.almeida@collabora.com, faith.ekstrand@collabora.com, boris.brezillon@collabora.com, lina@asahilina.net, mcanal@igalia.com, zhiw@nvidia.com, acurrid@nvidia.com, cjia@nvidia.com, jhubbard@nvidia.com, airlied@redhat.com, ajanulgu@redhat.com, lyude@redhat.com, linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: e8xmbz9m4wet8ud6nkwki7tmckqpcwok X-Rspamd-Queue-Id: 4F9B84002E X-Rspamd-Server: rspam11 X-HE-Tag: 1722516546-860852 X-HE-Meta: U2FsdGVkX1+Zaq+E++EYSfgkdriZoPdi0h3gxEcSyIUsRAEIZpOke9AoObtAzHhcaDDKYmxolwBCQ4fDBjBQc44MLaxvCnjbPXMhRqPGAMtKGYzJ8Hu2Rzx8DMZZR/KNdsJGMlQdKpyKpUpUoLW6eAo0lleSCVMnsQbmzevQZ5eroCngB7i4CFEKMhktrYt4rD7ZO1gSEs31tPHgsSLITZMjx6meGXg5kCwu7HiTp1BCWfkTpTcoam9K7roPM5Oe8LLUK4MZzpab30DyNZICI5Uu3wZSTJBafW6eYvrbpLnVQXXBElIrbl19H1G0o3ySlo4XaI/p0BDAhzqMRh2fWnoejXTeBj85Fy05O+Z96skOKMPi5m0Rgab1ww5QxzEJpggO5RWW5yJFcabFVLpESUMDmnOdrVHq1Ct7U6a6nRnJpBUPHnwPwxM4QHRI5zihg9/Qxo7l7A3y74k7Idb1/FX43/6X2b7lX/N4oTNJA9jNgdWdzqyALQJRDmayORkCKC4i2uaJimzBH2VCCR12xq9APZtUqPBbvwYZ7fzy7IuNBiDQV96KkdfrPyNwabi4BI3A97AzrsyGj9g29w20JRDy4M8yVvXFoMwLvcgWJSIRex6RAOhMu0kAH/ez0aCs0jr0pcjI3a/ORrrmp2d4lom8eqAkjSo3lYxOAIOCbcgX54u8NM78TdKDSbndOtVixXZSx2S+l0nWeHTfYNANC6npqmH9GAfZO45ntbT4Evvogy+L4pLcPuhBNqX+WfVUnrA9bXlRE3fIubMNHe4H0o4ET8zpQKgag2naw1rXnn/TVhsGV5ytYIPWcKkiLLDIUG0nsibe2U0vr26QZatNTFGXIxSiTNXyUiXFua4OP376BHdLEC8SbT9+Xf1GEFzXviBHLMr8RddLthyKGR82HWGCy5KbsUpoJi5KqzV2UAjsRLDnngTHh8/xywjP+yoExRdu6jFtBF3/p6jW4jN TxOWVZYP AgFDZsO+0z6pwe4KolOa9pPD7hmS2vpWLODfeSg8iPeODk1wTO7pNNz6z8qhZUIWQV99fOzKB2/M2q868A1neAwXud+fY/BycxL1p4CB7kmEabGcEpDv/6CWE+PnnQcDcHqb9wVvhskTGHVRTVyIQVLTOhsfiq4Nr2cjtjm0j5VEdOTjFtmG+Rij0uqZcLXI/lzxwNQa39IF7QUVF40MxCNWrcJ6iRuZlhGSO0Mew5msbqfhkDDbkzb4Ie982XkmYknELIigHHadyBwQjoXZedPJOJEQhnniY3lrwNdkbOnFEm550UOK6yvNoPqWa9l4ZKCd289Byt/5zaeI= X-Bogosity: Ham, tests=bogofilter, spamicity=0.347343, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 1, 2024 at 2:45=E2=80=AFPM Danilo Krummrich w= rote: > > On Thu, Aug 01, 2024 at 10:55:51AM +0200, Alice Ryhl wrote: > > On Thu, Aug 1, 2024 at 2:07=E2=80=AFAM Danilo Krummrich wrote: > > > + /// Converts a `Box` into a `Pin>`. > > > + #[inline] > > > + pub fn into_pin(b: Self) -> Pin > > > + where > > > + A: 'static, > > > + { > > > + // SAFETY: It's not possible to move or replace the insides = of a `Pin>` when > > > + // `T: !Unpin`, so it's safe to pin it directly without any = additional requirements. > > > + unsafe { Pin::new_unchecked(b) } > > > + } > > > > In the standard library, this functionality is provided using the From > > trait rather than an inherent method. I think it makes sense to match > > std here. > > I already provide `impl From> for Pin>` in this= patch, > which just calls `Box::into_pin`. Ah, ok, I might drop into_pin and only have From, but I'm ok either way. > > > +impl ForeignOwnable for crate::alloc::Box > > > +where > > > + A: Allocator, > > > +{ > > > + type Borrowed<'a> =3D &'a T; > > > + > > > + fn into_foreign(self) -> *const core::ffi::c_void { > > > + crate::alloc::Box::into_raw(self) as _ > > > + } > > > + > > > + unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> &'a T { > > > + // SAFETY: The safety requirements for this function ensure = that the object is still alive, > > > + // so it is safe to dereference the raw pointer. > > > + // The safety requirements of `from_foreign` also ensure tha= t the object remains alive for > > > + // the lifetime of the returned value. > > > + unsafe { &*ptr.cast() } > > > + } > > > + > > > + unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self { > > > + // SAFETY: The safety requirements of this function ensure t= hat `ptr` comes from a previous > > > + // call to `Self::into_foreign`. > > > + unsafe { crate::alloc::Box::from_raw(ptr as _) } > > > + } > > > +} > > > > You may want to also implement ForeignOwnable for Pin>. See: > > https://lore.kernel.org/all/20240730-foreign-ownable-pin-box-v1-1-b1d70= cdae541@google.com/ > > Yeah, I think I've also seen another patch that it about to add a functio= n to > convert a `Box` back into uninit state. > > Depending how fast you need ForeignOwnable for Pin>, do you prefer= to > contribute a corresponding patch to this series? It's easiest for me if you just add it to this patch of your series. I don't care about credit in this particular case. Alice