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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-rust@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: QEMU Rust-related patches and discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-rust-bounces+qemu-rust=archiver.kernel.org@nongnu.org Sender: qemu-rust-bounces+qemu-rust=archiver.kernel.org@nongnu.org On 8/7/25 14:29, Manos Pitsidianakis wrote: >> +//! Bindings for `rcu_read_lock` and `rcu_read_unlock`. >> +//! More details about RCU in QEMU, please refer docs/devel/rcu.rst. >> + > > How about a RAII guard type? e.g. RCUGuard and runs `rcu_read_unlock` on Drop. Clippy says Rcu not RCU. :) You're right, not just because it's nice but also because it bounds the dereference of the FlatView. Something like this build on top of the guard object: pub struct RcuCell { data: AtomicPtr } impl RcuCell { pub fn raw_get(&self) -> *mut T { self.data.load(Ordering::Acquire) } pub fn get<'g>(&self, _: &'g RcuGuard) -> Option<&'g T> { unsafe { self.raw_get().as_ref() } } } Using this is a bit ugly, because you need transmute, but it's isolated: impl AddressSpace { pub fn get_flatview(&self, rcu: &'g Guard) -> &'g FlatView { let flatp = unsafe { std::mem::transmute::<&*mut FlatView, &RcuCell>( &self.0.as_ptr().current_map) }; flatp.get(rcu) } } impl GuestAddressSpace for AddressSpace { fn memory(&self) -> Self::T { let rcu = RcuGuard::guard(); FlatViewRefGuard::new(self.get_flatview(rcu)) } } > Destructors are not guaranteed to run or run only once, but the former > should happen when things go wrong e.g. crashes/aborts. You can add a > flag in the RCUGuard to make sure Drop runs unlock only once (since it > takes &mut and not ownership) Yeah I think many things would go wrong if Arc could run its drop implementation more than once. Paolo