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Fri, 05 Dec 2025 03:30:12 -0800 (PST) X-Google-Smtp-Source: AGHT+IEVk4Sk3ZH8EZ7nLY0EfKsXpUeYumaLoiZzPfJIfkt92k7CRko8I5Tw/cPt6bXDTJ3JrWlj/Q== X-Received: by 2002:a05:600c:a07:b0:477:9890:9ab8 with SMTP id 5b1f17b1804b1-4792eb10ddcmr63074515e9.3.1764934211730; Fri, 05 Dec 2025 03:30:11 -0800 (PST) Received: from [192.168.10.48] ([176.206.119.13]) by smtp.googlemail.com with ESMTPSA id 5b1f17b1804b1-47930c7473bsm125829785e9.10.2025.12.05.03.30.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 05 Dec 2025 03:30:11 -0800 (PST) Message-ID: <27641d41-010d-4239-a84e-4b7724f3c30a@redhat.com> Date: Fri, 5 Dec 2025 12:30:10 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 02/14] rust: add basic QObject bindings From: Paolo Bonzini To: Zhao Liu Cc: qemu-devel@nongnu.org, qemu-rust@nongnu.org, armbru@redhat.com, marcandre.lureau@redhat.com References: <20251001075005.1041833-1-pbonzini@redhat.com> <20251001080051.1043944-3-pbonzini@redhat.com> <382ef69e-50b7-4a7f-aa9d-63c076a737f3@redhat.com> Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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_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-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 12/4/25 15:18, Paolo Bonzini wrote: > On 12/4/25 15:15, Zhao Liu wrote: >>> diff --git a/rust/util/src/qobject/mod.rs b/rust/util/src/qobject/mod.rs >>> new file mode 100644 >>> index 00000000000..f43d87a3b66 >>> --- /dev/null >>> +++ b/rust/util/src/qobject/mod.rs >>> @@ -0,0 +1,309 @@ >>> +//! `QObject` bindings >>> +//! >>> +//! This module implements bindings for QEMU's `QObject` data >>> structure. >>> +//! The bindings integrate with `serde`, which take the role of >>> visitors >>> +//! in Rust code. >>> + >>> +#![deny(clippy::unwrap_used)] >> >> Are there are any specific considerations for this lint rule? > > It ensures that all conversion errors (e.g. from try_into()) are > propagated. > >>> +pub struct QObject(&'static UnsafeCell); >> >> It seems Opaque<> feels more natural than UnsafeCell<>. >> >> Opaque::from_raw() requires *mut T, but QObject::from_raw() and >> QObject::clone_from_raw() mainly play with C bindings which usually use >> *mut pointer. So it seems unnecessary to convert *mut to *const in the >> middle. >> >> And furthermore, I think QObject(Opaque) is better >> than QObject(&'static Opaque). From a semantic view, >> C's QObject is a struct, while Rust's QObject is a reference, which seems >> somewhat mismatched. >> >> I'm not sure yet if there may be gaps when remove &'static, but it >> looks like using &'static Opaque<> instead of &'static UnsafeCell<> is >> Okay in code? > > I am using UnsafeCell because the QObject here is always valid, i.e. > MaybeUninit is explicitly not necessary.  Opaque explicitly allows it to > be invalid, here instead the API is "create via C code or FFI and only > then create the QObject". > > However, while it is possible to use Opaque<> instead of UnsafeCell<>, > it is not possible to make this a simple wrapper because QObject is > unmovable and reference counted.  That is, QObject is the equivalent of > (for example) Owned. > >> These 2 methods are the clone, but it seems they're actually similar to >> Owned<>, i.e., increase refcnt when Rust side wants to "own" or ensure >> to use this safely. >> >> However, there indeed isn't a non-object version of Owned for now, so I >> think this kind of clone should be okay. Hmm, for long-term, is it >> valuable to consider a more generic Owned<>? > > Linux has ARef<> I think.  But it seems overkill for now. > >>> +impl FromIterator for QObject >>> +where >>> +    Self: From, >>> +{ >>> +    fn from_iter>(it: I) -> Self { >> >> nit: maybe the name "iter" is better than "it"? > > Sure. > >>> +                    match qnum__.kind { >>> +                        $($crate::bindings::QNUM_I64 => break { >>> +                            let $i64var = unsafe { qnum__.u.i64_ }; >>> +                            $i64 >>> +                        },)? >>> +                        $($crate::bindings::QNUM_U64 => break { >>> +                            let $u64var = unsafe { qnum__.u.u64_ }; >>> +                            $u64 >>> +                        },)? >>> +                        $($crate::bindings::QNUM_DOUBLE => break { >>> +                            let $f64var = unsafe { qnum__.u.dbl }; >>> +                            $f64 >>> +                        },)? >>> +                        _ => {} >> >> I think this doesn't handle a special case: qobj's QNUM type doesn't >> macth the value type, for example, qobj is QNUM_U64 but value is i64. >> >> Though external code won't use this macro, I think panic may be better >> than {}?> Thurther, there're 2 match blocks. Could we merge them as one? Just one thing: it's not returning {}, it's returning the value expressed in $(_ => $other:expr,)?. So I think it's better to keep it this way. Paolo