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[2003:d8:2f37:2b00:948c:dd9f:29c8:73f4]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3cf33fb9dbfsm15756340f8f.43.2025.09.01.08.52.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 01 Sep 2025 08:52:52 -0700 (PDT) Message-ID: <001833dc-ee02-4bd3-8a37-820d0cd56be0@redhat.com> Date: Mon, 1 Sep 2025 17:52:47 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 02/12] mm: constify pagemap related test functions for improved const-correctness To: Vlastimil Babka , Lorenzo Stoakes , Max Kellermann Cc: akpm@linux-foundation.org, axelrasmussen@google.com, yuanchu@google.com, willy@infradead.org, hughd@google.com, mhocko@suse.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Liam.Howlett@oracle.com, rppt@kernel.org, surenb@google.com, vishal.moola@gmail.com, linux@armlinux.org.uk, James.Bottomley@hansenpartnership.com, deller@gmx.de, agordeev@linux.ibm.com, gerald.schaefer@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, davem@davemloft.net, andreas@gaisler.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, chris@zankel.net, jcmvbkbc@gmail.com, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, weixugc@google.com, baolin.wang@linux.alibaba.com, rientjes@google.com, shakeel.butt@linux.dev, thuth@redhat.com, broonie@kernel.org, osalvador@suse.de, jfalempe@redhat.com, mpe@ellerman.id.au, nysal@linux.ibm.com, linux-arm-kernel@lists.infradead.org, linux-parisc@vger.kernel.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-fsdevel@vger.kernel.org References: <20250901123028.3383461-1-max.kellermann@ionos.com> <20250901123028.3383461-3-max.kellermann@ionos.com> <26cb47bb-df98-4bda-a101-3c27298e4452@lucifer.local> <8e3f20bf-eda7-496c-9fb2-60f5f940af22@lucifer.local> <925480c3-d0ff-4f24-ada0-966ad9a83080@suse.cz> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 01.09.25 17:47, Vlastimil Babka wrote: > On 9/1/25 17:14, Lorenzo Stoakes wrote: >> On Mon, Sep 01, 2025 at 04:50:50PM +0200, Max Kellermann wrote: >>> On Mon, Sep 1, 2025 at 4:25 PM Lorenzo Stoakes >>> wrote: >>>> 1. (most useful) Const pointer (const *) means that the dereffed >>>> value is const, so * = or -> = are prohibited. >>> >>> Only this was what my initial patch was about. >> >> Right agreed then. >> >>> >>>> 2. (less useful) We can't modify the actual pointer value either, so >>>> e.g. = is prohibited. >>> >>> This wasn't my idea, it was Andrew Morton's idea, supported by Yuanchu Xie: >>> https://lore.kernel.org/lkml/CAJj2-QHVC0QW_4X95LLAnM=1g6apH==-OXZu65SVeBj0tSUcBg@mail.gmail.com/ >> >> Andrew said: >> >> "Not that I'm suggesting that someone go in and make this change." >> >> And Yuanchu said: >> >> "Longer function readability would benefit from that, but it's IMO infeasible to >> do so everywhere." >> >> (he also mentions it'd be good if gcc could wran on it). >> >> So this isn't quite true actually. > > I understood it the same, that it would be nice if gcc treated incoming > params (i.e. pointers, not pointed-to values) as const and warn otherwise, > but not suggesting we should start doing that manually. > > I personally agree that adding those extra "const" is of little value and > makes the function definition lines longer and harder to read and so would > rather not add those. > > I mean we could first collectively decide (and that's not a review > half-suggesting we do them) that we want them, and document that, but AFAIK > that's not the case yet. While there's already an agreement that const > pointed-to values is a good thing and nobody objects that. Yeah, and discussed elsewhere in this series, it would also have to be clarified how to deal with the *const" (or const values in general) with function declaration vs. definition. I don't think we really have written-down rule for that yet. -- Cheers David / dhildenb