From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yb1-f201.google.com (mail-yb1-f201.google.com [209.85.219.201]) (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 D252D2837B for ; Sat, 27 Jul 2024 20:30:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.219.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722112256; cv=none; b=mwddjtijK++yFatE1qAm6BlqfedMHoA9K/te7ZNMiB09qu2odjfK6v2Vor0jpgJSzOqSQZ+bC3YrpoQduLlekmGOnOBVId+7Qxm92oiispUXBGCcVv0TNaNLRDvICbsuRUwz/k268La1C83eVTCgTQS86Jt1P60/ox+Lb1f7S2k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722112256; c=relaxed/simple; bh=JMYAJfnvh5fBjtCAE9lnpRby5Iz4gLoiR7otAicAG7Q=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=XWLtwTd1mil6wA1P6tUruKzmlaUR4EbvhLQGaMfVhsXt0sXQmEDheMLZRtwgRHv0rTEXNUpT8+1h2fIa8jv/S+L0OXnVgpb7TUkW3xctQnxtYR22LfCrbsiw6VD1f7nHsqkrdRmLexEusLIe6bhMNaupDsT1s82+0NOWT9V981c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--mattgilbride.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=AN5pXvlL; arc=none smtp.client-ip=209.85.219.201 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--mattgilbride.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="AN5pXvlL" Received: by mail-yb1-f201.google.com with SMTP id 3f1490d57ef6-e0b2af9de57so1653792276.3 for ; Sat, 27 Jul 2024 13:30:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1722112254; x=1722717054; 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=nsba2l+mTog8DKmlCLg5ao+hwsKRjwNNTQ3oaykOYeU=; b=AN5pXvlLRuRwkGJ8ZnkhIEEzrhFazra0EcOXiCxHpZrqbuFKBAyT4FgaX7YFSDZLBj YzVFVG+niIAnl6zj5ZVtYiQ/3guqBWqlm3OJmLwAPtShuhnG/1dO+AfxkgDl49y0M7bF avV1uz55gUUgeLB1sUHqAazYYjI414lu9azj5RXjVn88arvB2/noBQrio43amdWFq1xS Hrz1DojZ0b+8n8Uwmn8dk8xi8HqoU+Fh7mrsbovacws5oHr53egCM6F/Sw31VHP+p+wa j65EznzWqy9iNRiGzuildY4qLxZXz8QDMtslalXOtvOVxammW30wSgVoZmSUljHlVTuK DooA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1722112254; x=1722717054; 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=nsba2l+mTog8DKmlCLg5ao+hwsKRjwNNTQ3oaykOYeU=; b=BichMTLF43fmOV2X00WeN/+pAEQOS/hppgKNl9kCBTDBeByGcnScJc+bd3JkMt+1kG xRlwX4mXE3hQbeQXipchurtWjr4JY6Mfs4ohD2plmchmqfCBWu/uP2JF42rvR4UmAISH EWBr/hg9wOY6yx1hmDsYG2AUsTglT9t928w30Za6sia3CrnGkjtvzs+IN6YKttq4WKCu p7iW5OsFaFQjTyAVz2F5NJ2ChGt3/5eXXhxvILUceTFuwVi6AmSya0WoyxgtDyzgBmZp /CYx3U7Bh23Omynn86NaSGP3rXEcDAqtFZZyDc1nh4LyIu7lV2bX9W6bqqxEOX9M1l8Z ETxw== X-Forwarded-Encrypted: i=1; AJvYcCVMiSf4Avk9oPlUya8j305SToPPTdF/R3tARBmv5soJG/MatJjYYCIlDsA531Z1nvvlSIeTaihrYNnqJIFMcTnR+8gVRAx0VAFNNMrlZiY= X-Gm-Message-State: AOJu0YzZ81pSpeISCNq6QmOMbQ942jv9QndhWHHEEaTdmsGVPrD+oxFK GLD1NLW7YFPKSmwTXWfKSq1/UVw1PEuJGCMlEMeYtPJiJDNLQkJZmHEsEP0lMva0QL34P/I8GMr mmQZGzNwULV2wjxteCPz98rkr/g== X-Google-Smtp-Source: AGHT+IHpu7bjRnigEBEh0qhoPcCoGcFLnuGxtsTcc9qvNxSWHxq1NqzBuyWbVE6j5NNmPxREKIAuQuV4TpRKm7sYoyI= X-Received: from mattgilbride.c.googlers.com ([fda3:e722:ac3:cc00:2b:7d90:c0a8:2ac5]) (user=mattgilbride job=sendgmr) by 2002:a25:868f:0:b0:e08:6c33:7334 with SMTP id 3f1490d57ef6-e0b5454caa4mr86236276.8.1722112253919; Sat, 27 Jul 2024 13:30:53 -0700 (PDT) Date: Sat, 27 Jul 2024 20:30:46 +0000 In-Reply-To: <20240727-b4-rbtree-v8-0-951600ada434@google.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240727-b4-rbtree-v8-0-951600ada434@google.com> X-Mailer: b4 0.13.0 Message-ID: <20240727-b4-rbtree-v8-1-951600ada434@google.com> Subject: [PATCH v8 1/6] rust: kernel: add `drop_contents` to `BoxExt` From: Matt Gilbride To: Miguel Ojeda , Alex Gaynor , Wedson Almeida Filho , Boqun Feng , Gary Guo , "=?utf-8?q?Bj=C3=B6rn_Roy_Baron?=" , Benno Lossin , Andreas Hindborg , Alice Ryhl , Greg Kroah-Hartman , "=?utf-8?q?Arve_Hj=C3=B8nnev=C3=A5g?=" , Todd Kjos , Martijn Coenen , Joel Fernandes , Carlos Llamas , Suren Baghdasaryan , Christian Brauner Cc: Rob Landley , Davidlohr Bueso , Michel Lespinasse , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, Matt Gilbride Content-Type: text/plain; charset="utf-8" From: Benno Lossin Sometimes (see [1]) it is necessary to drop the value inside of a `Box`, but retain the allocation. For example to reuse the allocation in the future. Introduce a new function `drop_contents` that turns a `Box` into `Box>` by dropping the value. Signed-off-by: Benno Lossin Link: https://lore.kernel.org/rust-for-linux/20240418-b4-rbtree-v3-5-323e134390ce@google.com/ [1] --- rust/kernel/alloc/box_ext.rs | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/rust/kernel/alloc/box_ext.rs b/rust/kernel/alloc/box_ext.rs index 829cb1c1cf9e..557895db4f48 100644 --- a/rust/kernel/alloc/box_ext.rs +++ b/rust/kernel/alloc/box_ext.rs @@ -4,7 +4,7 @@ use super::{AllocError, Flags}; use alloc::boxed::Box; -use core::mem::MaybeUninit; +use core::{mem::MaybeUninit, ptr}; /// Extensions to [`Box`]. pub trait BoxExt: Sized { @@ -17,6 +17,20 @@ pub trait BoxExt: Sized { /// /// The allocation may fail, in which case an error is returned. fn new_uninit(flags: Flags) -> Result>, AllocError>; + + /// Drops the contents, but keeps the allocation. + /// + /// # Examples + /// + /// ``` + /// use kernel::alloc::flags; + /// + /// let value = Box::new([0; 32], flags::GFP_KERNEL); + /// let value = value.unwrap().drop_contents(); + /// // Now we can re-use `value`: + /// Box::write(value, [1; 32]); + /// ``` + fn drop_contents(self) -> Box>; } impl BoxExt for Box { @@ -53,4 +67,12 @@ fn new_uninit(flags: Flags) -> Result>, AllocError> { // zero-sized types, we use `NonNull::dangling`. Ok(unsafe { Box::from_raw(ptr) }) } + + fn drop_contents(self) -> Box> { + let ptr = Box::into_raw(self); + // SAFETY: `ptr` is valid, because it came from `Box::into_raw`. + unsafe { ptr::drop_in_place(ptr) }; + // SAFETY: `ptr` is valid, because it came from `Box::into_raw`. + unsafe { Box::from_raw(ptr.cast()) } + } } -- 2.46.0.rc1.232.g9752f9e123-goog