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Wed, 08 Apr 2026 04:10:55 -0700 (PDT) Date: Wed, 8 Apr 2026 13:10:53 +0200 From: Petr Mladek To: Song Liu Cc: Yafang Shao , Joe Lawrence , Dylan Hatch , jpoimboe@kernel.org, jikos@kernel.org, mbenes@suse.cz, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, kpsingh@kernel.org, mattbobrowski@google.com, jolsa@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, memxor@gmail.com, yonghong.song@linux.dev, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [RFC PATCH 3/4] livepatch: Add "replaceable" attribute to klp_patch Message-ID: References: Precedence: bulk X-Mailing-List: live-patching@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue 2026-04-07 16:09:39, Song Liu wrote: > On Tue, Apr 7, 2026 at 8:08 AM Petr Mladek wrote: > [...] > > > + * @replace: replace tag: > > > + * = 0: Atomic replace is disabled; however, this patch remains > > > + * eligible to be superseded by others. > > > > This is weird semantic. Which livepatch tag would be allowed to > > supersede it, please? > > > > Do we still need this category? > > > > > + * > 0: Atomic replace is enabled. Only existing patches with a > > > + * matching replace tag will be superseded. > > > * @list: list node for global list of actively used patches > > > * @kobj: kobject for sysfs resources > > > * @obj_list: dynamic list of the object entries > > > @@ -137,7 +141,7 @@ struct klp_patch { > > > struct module *mod; > > > struct klp_object *objs; > > > struct klp_state *states; > > > - bool replace; > > > + unsigned int replace; > > > > This already breaks the backward compatibility by changing the type > > and semantic of this field. > > I was thinking if replace=0 means no replace, it is still backward > compatible. Did I miss something? IMHO, the semantic of the no-replace mode would be strange if we introduce the hybrid mode. Especially, it would be strange when it can be replaced by any livepatch with random replace tag/set. Also it would just complicate the definition and detection of conflicts. I am going to provide more details in the reply to Yafang. Best Regards, Petr