From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=209.85.222.52 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793209470; b=cgLUE2LBjiXQvwvYs6lAs3SvpXLGjfw2ilky68JA7qMTz395zqK4Bh/j1+5Gyy1wsHv0 taUukwIVlXFGqHsV8sobDUSQLLgZH8Z/vj0JmBy9u9SvJJhec79xLKpDsJhRoewmo7ia0 56daflCXYuz73FXg8mzcK5GPNiSx0vX3mIM5K4umatm+sjkrMmdui8bwRY1FW6mJ8q6Kj u1xATUOR1A5moBK4JAxW3a7PZDQ4MOKE8GKGzvTuJgkMDFHSobJLXpCjIniTx1mtSPFXB zapAdXocfnSY654tTmzGuYu8fETjg7MmK9BSWtDSUOLzZKf012Ezu5n/5d9KTer3Pvw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793209470; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received:Received: Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:Content-Transfer-Encoding: In-Reply-To; bh=s56cw49H74YOeay3n+CLmJxr96H3PjfrjsaPdtr6E80=; b=F0DNvg9hGHIcE0/RqkDNuUwafoY6S8Cn10F9TzyNKu7ntBPqRxXdiXZMpxG5VUhpuxvS x6R7wzFNgaTDoQljS1qrrkJQIEFAU4PMF9U+++13H9lr3XLKsLRd4qXYz3B68koH4fhUh /tEche94znFtNRImN9T8pdc0JOLskMc6Drk2zehnDms4WFrToEcRsq11vMEjenKAFMjQw 7uErSyC2CD2KoEgeRysThvKlfqDVAoBeP7s1FizLKgdtnpvF1qWAVIZkopTQ2bsHz07+f P75xwtyxamGdusztrVBlggaY23Jj3xZjKikQLLNIKElaWXYsgT3DykXF4/x80UNsiyg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=soleen.com; spf=pass smtp.mailfrom=soleen.com; dkim=pass header.d=soleen.com header.i=@soleen.com header.a=rsa-sha256 header.s=google header.b=iJy5kuJI; arc=none smtp.remote-ip=209.85.222.52 Received: from mail-ua1-f52.google.com (mail-ua1-f52.google.com [209.85.222.52]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7E381606A326 for ; Wed, 28 Oct 2026 17:44:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 7E381606A326 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=soleen.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=soleen.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=soleen.com header.i=@soleen.com header.a=rsa-sha256 header.s=google header.b=iJy5kuJI Received: by mail-ua1-f52.google.com with SMTP id a1e0cc1a2514c-990a39ba4fbso369337241.0 for ; Wed, 28 Oct 2026 10:44:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=soleen.com; s=google; t=1793209469; x=1793814269; darn=vger.kernel.org; h=in-reply-to:content-transfer-encoding:content-disposition :content-type:mime-version:references:message-id:subject:cc:to:from :date:from:to:cc:subject:date:message-id:reply-to:content-type; bh=s56cw49H74YOeay3n+CLmJxr96H3PjfrjsaPdtr6E80=; b=iJy5kuJIKEFoVGXIv0G1W+lcBvi4+8Xg3Up72eyRWsM34ppCddP5ilpekezxnMXx54 wNVtglNWl1Juw56jX8SNwQS7WZKs9Y2X61a375wMFfYgiH4i03Atn7I+ij8S+kLhqtfT l07FNZinyoqAk6s+eVtDRNFkKCg8ONt5X560obpxpG2ZC7VnPvjzuP7bhaeVMMRQaZQf bnvIZGVN+qVBNlncKqiFZBQ2j+79seozjiyPSZgLY1TuGDnPTDoB10ATDbxfyjixqlJz vdOfv2Qybh76j3dxSW1ILlTknOlei2s6oL7+i6Y7LDLEJWeTZKkbkP+obWZ+cP33y8/P 9s8A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1793209469; x=1793814269; h=in-reply-to:content-transfer-encoding:content-disposition :content-type:mime-version:references:message-id:subject:cc:to:from :date:x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to:content-type; bh=s56cw49H74YOeay3n+CLmJxr96H3PjfrjsaPdtr6E80=; b=Mnc1FfNJwfzDLyQUPh7ZcsMORar2EbEX+Yag13LcvAwi5ICfwcy6uqudel9csj2vpZ Y/cXJhSA5eKSiE+rGb5QgodaQ5bgVfzRIBAqottzpaFnlcjFuQ2JBmUBfgry4eoJmymq EHzT5mzxEryoR9YaZImMTkXf28FwTx8CWM1qsc+4FwmUP8cSBenSI0caKGwHRWJ+Pstc Aa2rT5f4SjXt89M16ErKAF3CZGyYUWsEu+olEYqz4jpvmq8EQEpxd5anojOKq3mIpEVW Eyjke4avYMPbOdEM+RDvICwLuY55/PFLiztJaZDYWCrzCq5dfvkSrLdjoMYA82JoBGbq 6SjQ== X-Forwarded-Encrypted: i=1; AKwUvBzLryY2RTdQqCQwFNieUtwO7diYtkIW7Jknd99mkxJmCBNziEm+T9IVkaL8r6oFqUi4ternPrSqH386xRQ=@vger.kernel.org X-Gm-Message-State: AFq9FYLwIN0i+btOk6dFFB4WBu/jX8PXOXa5JrENqtMAcYUYX3U8xBe6 CCiTQ7cmbEgPrnC5Nr6hTijSyvJdQGSITk2FfClnCquriaG9D70+SRZjwdJb52PCvTM= X-Gm-Gg: AYBFou3qIAid8X+wQpQZ+5CUjseWKABkR9YD+cAqizrL+DAnsJ2iF6XKBz4KZ33VKnN KAwTnDZFBX0gBwlyGN6iYQGVa9HAsfCn++F95jQjL0YLBLw1chSgAot7CZVTZ8ZRKDpg04PmOW3 e1qoQ7I/AYKHnf8VFwUR+jnv+r2AHQG1nsuRwkoPI0MKroYkU8R0mquEqrO0+WIePWiGYBEno9/ uFG2CH4crIf2JyU92ffsuCg1VHlgtBWe2rcMjVsef/+5h2M8KZIDJAhSwZcmklpVpelw68pjgGy XkBe1BygOIW2mKyvQhlSRVHCShs/deXTpSFeVyH2gMqsbnsurRoh5aTPnd043wz+0XJXfIBYxAv xiP7JkVDbhoudVHmvQ5ZJSUbU2TuIqrWT5wtfKcF2OIhXLnecsai1vBT9v4wvfeeKnqOqI7IlNM +mMSU+acuWzLL5y78vG4Vhoh4w3kBKLKb9zy6jTqdHvFOYBLRNdF3VCNVHSh2bJSglas07A7bKM 7SuVCr0Py5l4pXEiorDGheOnm0dxc6MOC94WtH+TY0/6Vkglwr8fNgmKQUHxNCpduGLEyroO/MT 7fmV4FQ76HlgKmN16rGlzUDzwTvstwEv6t5zoyltPFdCPuDhyrWHbJmustJ4o7XPIsdZl+PUE4q 9zU2OsiScQW3cdmV+teZcJ7kirSqEgDK4 X-Received: by 2002:a05:6102:3e8d:b0:7a5:7282:1994 with SMTP id ada2fe7eead31-7d03a50a85cmr1269510137.7.1793209468986; Wed, 28 Oct 2026 10:44:28 -0700 (PDT) Received: from google.com (64.167.245.35.bc.googleusercontent.com. [35.245.167.64]) by smtp.gmail.com with ESMTPSA id a1e0cc1a2514c-99125931983sm6616412241.2.2026.10.28.10.44.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Oct 2026 10:44:28 -0700 (PDT) Date: Wed, 28 Oct 2026 13:44:27 -0400 From: Pasha Tatashin To: Pratyush Yadav Cc: David Matlack , Pasha Tatashin , tarunsahu@google.com, Andrew Morton , joro@8bytes.org, Mike Rapoport , maz@kernel.org, arnd@arndb.de, jgg@nvidia.com, robin.murphy@arm.com, loganodell@google.com, oupton@kernel.org, kevin.tian@intel.com, alex@shazbot.org, dwmw2@infradead.org, pbonzini@redhat.com, seanjc@google.com, will@kernel.org, Alexander Graf , Bjorn Helgaas , baolu.lu@linux.intel.com, linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, sagis@google.com, linux-mm@kvack.org, kvmarm@lists.linux.dev, iommu@lists.linux.dev, linux-pci@vger.kernel.org, kexec@lists.infradead.org, skhawaja@google.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v2 3/4] liveupdate: Replace compatibility string with a 2-bit pair feature header Message-ID: References: <2vxz8q3hoicx.fsf@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <2vxz8q3hoicx.fsf@kernel.org> On 10-28 18:17, Pratyush Yadav wrote: > On Mon, Oct 26 2026, David Matlack wrote: > > > On 2026-10-25 04:38 PM, Pasha Tatashin wrote: > >> On Fri, Oct 23, 2026 at 9:50 AM David Matlack wrote: > > > [...] > >> The reason I care about keeping the header compact is that we are > >> defining a foundational kernel ABI and want to use this header across > >> almost every serialized data structure so we can evolve them later > >> without breaking compatibility. While some top-level structs are on > >> sparse folios today, other serialized structs are tightly packed, and > >> we are looking to add KHO slab support in the future where tightly > >> packed allocations will be common. > > > > My intuition is we will have a small number of headers per preserved > > file and per preserved FLB. One for the top-level struct and then > > optionally a few more for sub-structs like arch-specific data. That is > > why I am less worried 8 bytes per header, even if we fix the folio > > problem. > > > > Maybe where our visions differ is when there are collections of > > serialized structs, like KHO blocks. For collections I don't think the > > elements will each have their own headers. Otherwise the elements could > > be different sizes. > > kho_block today doesn't store entry_size in the serialized payload. It > relies on its caller to do so. With extensible structures, this can get > messy. Sure, the owner of the kho_block_set can track the size somewhere > in its payload, but perhaps we should store the size in > kho_block_header_ser to begin with? I agree, and we will discuss versioned vs. owned serialized data structures separately. With this series, we establish a common framework: size/feature flags and accessors, and we update most of our serialized structs to include them. All "shared" structs (e.g., KHO, FLB, radix-tree, block_sets, etc.) should have their own versioning. kho_block_header_ser should have this header. Pasha > > Anyway, not a problem this series needs to solve, but something we > should eventually do. > > [...] > > -- > Regards, > Pratyush Yadav