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Wysocki" Subject: Re: [PATCH v4 1/1] virt: acrn: Mark the uuid field as unused Message-ID: References: <20221116092254.66234-1-andriy.shevchenko@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-7.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 16, 2022 at 06:04:37PM +0200, Andy Shevchenko wrote: > On Wed, Nov 16, 2022 at 04:20:08PM +0100, Greg Kroah-Hartman wrote: > > On Wed, Nov 16, 2022 at 03:29:31PM +0200, Andy Shevchenko wrote: > > > On Wed, Nov 16, 2022 at 12:42:16PM +0100, Greg Kroah-Hartman wrote: > > > > On Wed, Nov 16, 2022 at 11:22:54AM +0200, Andy Shevchenko wrote: > > ... > > > > > > - * @uuid: UUID of the VM. Pass to hypervisor directly. > > > > > + * @uuid: Reserved (used to be UUID of the VM) > > > > > > > > If it's reserved, then don't you need to check for 0? > > > > > > Reserved in a way that it may content something we just don't care about. > > > > "reserved" in the kernel ioctls mean "must be 0 and we will test for it, > > otherwise this is an empty/useless field that can never be touched again > > in the future. > > > > Please spell it out in detail as to if you can ever use this later on, > > and what the kernel will do (if anything) if it is set. > > > > And if "the kernel ignores it" then that means these bytes are now > > "empty space never to be used again", right? > > Right, I will fix this in v5. > > ... > > > > > > + __u8 uuid[16]; > > > > > > > > You just changed the type here, so what is that going to break in > > > > userspace that depended on this being of a structure type and now it's > > > > an array? > > > > > > It's the same. The previous was hidden behind additional type level. > > > > Same size, yes. Same C structure definition, no. > > It doesn't matter, see below. > > > > > And no other kernel changes needed? Shouldn't you warn if this field is > > > > set? > > > > > > No, as pointed out in the commit message kernel never ever used this. > > > > That does not mean that userspace tools never did, right? You are > > changing the structure definition, what tool just broke? > > The only tool has been amended like a year ago, so the answer is none. > The commit message has links to the commits in question that made that > amendment. > > Maybe I should remove Fixes tags? In such case we will very much know > that no old tools will be run on the new kernel. Please remove "fixes" as this doesn't "fix" anything. thanks, greg k-h