From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f74.google.com (mail-wm1-f74.google.com [209.85.128.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 422C71E9906 for ; Fri, 21 Mar 2025 07:44:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742543053; cv=none; b=FZhKyAVVRqbYl9bNQJV+4T35pEN2iDHkPWZAajUpiBnPSpR25WiDlG1A5kO4WYLbEjCONzl00xgzjWET503caGmXLUI/uf4BeA7zfNA+zAz2YGdkhf3E7DeyIq/tjZt/pKE44qddla5MhP+qH+Jonta77YXMWjDgdkhLfpsbBuA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742543053; c=relaxed/simple; bh=BbW5J7bJ0F/6xzUhLBXbzsRHMWimzxpvWyckCSBAybc=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=frMGhfNqH5vsaCyPr4Du2C3UIDKMyQO7v8hha3BGzf1ExxAodP1GIz6gKaWCwgLOi3+Xpk9znaA8L5GzEhb9gHlQWLviNFdSosicDKY3X2HKbg3sf/LYXxP9wklY9S7iM9yexR0d5YQWFSUSdfi7SJ0WpMlA15OH8BXE8UDSXZ4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--aliceryhl.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=jIGI0wFR; arc=none smtp.client-ip=209.85.128.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--aliceryhl.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="jIGI0wFR" Received: by mail-wm1-f74.google.com with SMTP id 5b1f17b1804b1-43d4d15058dso9826045e9.0 for ; Fri, 21 Mar 2025 00:44:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1742543050; x=1743147850; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=RmkFRH9GaUbe55qgjxHC/Rqmku15Hvr0oI20CNeu9iU=; b=jIGI0wFRsZ4+E2Bx11Q4eidwSbuQO5QWMRDDNxhRTfbNCdbnFGJ+A0aVS9ayUM677N +Zk0EAhfqcf+3dnECR7/EIJxrWcNiXcriYBDrRfqPZ7MGNUyyruOF/GfVhlVEkBJFvde ucCLrjj/+GiKvkEBgp7pp3nvINoSnSB+f0BkD+VdG46Z6xfsC8ey/8DcYwwrXq6EWRs7 Y/v5iV+c4GxFtcF+I+nGgNeBK+6CRbUrRDzCOxmaKPAm/d2h6umVNfTNCqJetTrC6V6i 7m3cV5N/4cnPQOcd25FG06NgSv6Yzc/w6ecTFMi/WbqbiW9lJi0rLTSn7xmnHutg0+3Y 0Jsg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1742543050; x=1743147850; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=RmkFRH9GaUbe55qgjxHC/Rqmku15Hvr0oI20CNeu9iU=; b=XJmaYOUbJTVhc//TCkjAgaRgoa4HZcYdpWbCj9dZ3ttMmemMXWVQXkwS1tmNziJSAZ u7kJ87BamyFP639c1YerkEodfaH+bM/AWTyhL91RBuHJ/8rpLO7lqxsuahdC5uFXxq1H evrCcbPvmP3w+C+cVQ+/RnVV6EwjuviWJTaoIr2TX6MzL5cgMK7n7ZXMX0ixZnS0wJ/U a6vyglSghjI8oTThV3+DakE8HuMRdei4XReWpCXfDZAXGciXQ3ASACQ3lkNlRzdRfmbk q7nYTxaOhCqyjpHuf+tp+6NzzGNZEdgGbmB+fgpTIdI3XdGhJMsDWBgdSDOOKw2YWWMo uKcg== X-Forwarded-Encrypted: i=1; AJvYcCXykug+H1G8/8OLlwayowrNREuARikvGWhthdsjp3S5057aXWYFJVDGNcZOyh3gTCz2phWKuU/AErPYL4cdcg==@vger.kernel.org X-Gm-Message-State: AOJu0Yxu+Ydf12tm7BHbtu4HjaqTer8Bk4JXhafxFDecW2CJc1Ea91q6 HnfXOur1LlSuBbJptI9jK9giDRyOtHxLnv9zNJV7jhyAv7rtElfFQrMSKLTa8PNymgTPfBHu0VL fSkcD/3hPMJjRHQ== X-Google-Smtp-Source: AGHT+IHusjLFbM5ugVtWBOs5d/FRmaSn72gmCX4kY3Tdaw8+WjbGKM+n4bBd7V+17bKoax+DIVEKZdNpfjdZGdw= X-Received: from wmbgx13.prod.google.com ([2002:a05:600c:858d:b0:43d:8f:dd29]) (user=aliceryhl job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:4693:b0:43c:fda5:41e9 with SMTP id 5b1f17b1804b1-43d50a5237fmr14181765e9.31.1742543050715; Fri, 21 Mar 2025 00:44:10 -0700 (PDT) Date: Fri, 21 Mar 2025 07:44:08 +0000 In-Reply-To: Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: Message-ID: Subject: Re: [PATCH 2/5] rust: alloc: add Vec::pop From: Alice Ryhl To: Benno Lossin Cc: Danilo Krummrich , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" On Thu, Mar 20, 2025 at 10:11:09PM +0000, Benno Lossin wrote: > On Thu Mar 20, 2025 at 2:52 PM CET, Alice Ryhl wrote: > > This introduces a basic method that our custom Vec is missing. I expect > > that it will be used in many places, but at the time of writing, Rust > > Binder has six calls to Vec::pop. > > > > Signed-off-by: Alice Ryhl > > --- > > rust/kernel/alloc/kvec.rs | 31 +++++++++++++++++++++++++++++++ > > 1 file changed, 31 insertions(+) > > > > diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs > > index 95e752ed27395fce72d372976b74fb1b0e957194..9943358c70aa63f5ad7ed9782cb8879d7a80a8fb 100644 > > --- a/rust/kernel/alloc/kvec.rs > > +++ b/rust/kernel/alloc/kvec.rs > > @@ -302,6 +302,37 @@ pub fn push(&mut self, v: T, flags: Flags) -> Result<(), AllocError> { > > Ok(()) > > } > > > > + /// Removes the last element from a vector and returns it, or `None` if it is empty. > > + /// > > + /// # Examples > > + /// > > + /// ``` > > + /// let mut v = KVec::new(); > > + /// v.push(1, GFP_KERNEL)?; > > + /// v.push(2, GFP_KERNEL)?; > > + /// assert_eq!(&v, &[1, 2]); > > + /// > > + /// assert_eq!(v.pop(), Some(2)); > > + /// assert_eq!(v.pop(), Some(1)); > > + /// assert_eq!(v.pop(), None); > > + /// # Ok::<(), Error>(()) > > + /// ``` > > + pub fn pop(&mut self) -> Option { > > + let Some(len_sub_1) = self.len.checked_sub(1) else { > > + return None; > > + }; > > Isn't it possible to do:? > > let len_sub_1 = self.len.checked_sub(1)?; Yes, good catch. > > + > > + // INVARIANT: If the first `len` elements are valid, then the first `len-1` elements are > > Please add spaces around `-`. I can do that, but does it really read better? > > + // valid. > > + self.len = len_sub_1; > > + > > + // INVARIANT: This invalidates a value in this vector's allocation, but the Vec invariants > > + // do not require it to be valid because `self.len <= len_sub_1`. > > I don't think this should be an `INVARIANT` comment. Maybe we don't even > need it. I can drop the INVARIANT: prefix. Alice