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Wed, 19 Nov 2025 14:28:38 -0800 (PST) X-Google-Smtp-Source: AGHT+IEUv9WjeaAxngoexi4ww9b7KWOrfXw/ZpMWF9C6McfRh4wRXJElDz62UUL7iTkrYl+kIXO8Hw== X-Received: by 2002:a05:6000:2385:b0:42b:41dc:1b5d with SMTP id ffacd0b85a97d-42cb9a0bdf0mr360295f8f.25.1763591318406; Wed, 19 Nov 2025 14:28:38 -0800 (PST) Received: from [192.168.10.81] ([176.206.119.13]) by smtp.googlemail.com with ESMTPSA id ffacd0b85a97d-42cb7fd8baesm1478117f8f.39.2025.11.19.14.28.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 19 Nov 2025 14:28:37 -0800 (PST) Message-ID: <91bf0b22-33c4-46f7-95fa-f634eb069ea7@redhat.com> Date: Wed, 19 Nov 2025 23:28:31 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/5] rust/hpet: remove BqlRefCell around HPETTimer To: Zhao Liu Cc: qemu-devel@nongnu.org, qemu-rust@nongnu.org References: <20251117084752.203219-1-pbonzini@redhat.com> <20251117084752.203219-4-pbonzini@redhat.com> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; 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_H3=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-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 11/19/25 16:17, Zhao Liu wrote: >> - fn init_timer_with_cell(cell: &BqlRefCell) { >> - let mut timer = cell.borrow_mut(); >> - // SAFETY: HPETTimer is only used as part of HPETState, which is >> - // always pinned. >> - let qemu_timer = unsafe { Pin::new_unchecked(&mut timer.qemu_timer) }; >> - qemu_timer.init_full(None, CLOCK_VIRTUAL, Timer::NS, 0, timer_handler, cell); >> + fn init_timer(timer: Pin<&mut Self>) { >> + Timer::init_full( >> + timer, >> + None, >> + CLOCK_VIRTUAL, >> + Timer::NS, >> + 0, >> + timer_handler, >> + |t| &mut t.qemu_timer, >> + ); >> } > > I find this way could also work for BqlRefCell case: > > fn init_timer_with_cell(cell: &mut BqlRefCell) { > // SAFETY: HPETTimer is only used as part of HPETState, which is > // always pinned. > let timer = unsafe { Pin::new_unchecked(cell) }; > Timer::init_full( > timer, > None, > CLOCK_VIRTUAL, > Timer::NS, > 0, > timer_handler, > |t| { > assert!(bql::is_locked()); > &mut t.get_mut().qemu_timer > }, > ); > } Yes, but I'm still not sure what the final shape will be... I don't like this too much. > > So any other non-lockless timer can also use this interface to > initialize their BqlRefCell<>. > > (BTW, I find BqlRefCell::get_mut() / as_ref() missed bql::is_locked(). > right?) as_ptr() doesn't need it because the pointer can be dereferenced later. As to get_mut()... I think if you are the only owner, you should have the guarantee of being able to modify the content freely. This is true even if your &mut came from interior mutability. So, in the above case you only need &mut t.get_mut().qemu_timer. > I think it may be better to add doc about how to use this for > BqlRefCell<> case since there'll be no example after this patch.