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[83.57.170.65]) by smtp.gmail.com with ESMTPSA id z7sm32097403wrw.93.2020.09.16.03.17.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Sep 2020 03:17:53 -0700 (PDT) Subject: Re: [PATCH 2/3] hostmem-file: add readonly=on|off option To: Stefan Hajnoczi References: <20200804101244.1283503-1-stefanha@redhat.com> <20200804101244.1283503-3-stefanha@redhat.com> <8f7b344e-87a5-3260-ae71-96758270fb27@redhat.com> <20200916093133.GA749356@stefanha-x1.localdomain> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Autocrypt: addr=philmd@redhat.com; keydata= mQINBDXML8YBEADXCtUkDBKQvNsQA7sDpw6YLE/1tKHwm24A1au9Hfy/OFmkpzo+MD+dYc+7 bvnqWAeGweq2SDq8zbzFZ1gJBd6+e5v1a/UrTxvwBk51yEkadrpRbi+r2bDpTJwXc/uEtYAB GvsTZMtiQVA4kRID1KCdgLa3zztPLCj5H1VZhqZsiGvXa/nMIlhvacRXdbgllPPJ72cLUkXf z1Zu4AkEKpccZaJspmLWGSzGu6UTZ7UfVeR2Hcc2KI9oZB1qthmZ1+PZyGZ/Dy+z+zklC0xl XIpQPmnfy9+/1hj1LzJ+pe3HzEodtlVA+rdttSvA6nmHKIt8Ul6b/h1DFTmUT1lN1WbAGxmg CH1O26cz5nTrzdjoqC/b8PpZiT0kO5MKKgiu5S4PRIxW2+RA4H9nq7nztNZ1Y39bDpzwE5Sp bDHzd5owmLxMLZAINtCtQuRbSOcMjZlg4zohA9TQP9krGIk+qTR+H4CV22sWldSkVtsoTaA2 qNeSJhfHQY0TyQvFbqRsSNIe2gTDzzEQ8itsmdHHE/yzhcCVvlUzXhAT6pIN0OT+cdsTTfif MIcDboys92auTuJ7U+4jWF1+WUaJ8gDL69ThAsu7mGDBbm80P3vvUZ4fQM14NkxOnuGRrJxO qjWNJ2ZUxgyHAh5TCxMLKWZoL5hpnvx3dF3Ti9HW2dsUUWICSQARAQABtDJQaGlsaXBwZSBN YXRoaWV1LURhdWTDqSAoUGhpbCkgPHBoaWxtZEByZWRoYXQuY29tPokCVQQTAQgAPwIbDwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4AWIQSJweePYB7obIZ0lcuio/1u3q3A3gUCXsfWwAUJ KtymWgAKCRCio/1u3q3A3ircD/9Vjh3aFNJ3uF3hddeoFg1H038wZr/xi8/rX27M1Vj2j9VH 0B8Olp4KUQw/hyO6kUxqkoojmzRpmzvlpZ0cUiZJo2bQIWnvScyHxFCv33kHe+YEIqoJlaQc JfKYlbCoubz+02E2A6bFD9+BvCY0LBbEj5POwyKGiDMjHKCGuzSuDRbCn0Mz4kCa7nFMF5Jv piC+JemRdiBd6102ThqgIsyGEBXuf1sy0QIVyXgaqr9O2b/0VoXpQId7yY7OJuYYxs7kQoXI 6WzSMpmuXGkmfxOgbc/L6YbzB0JOriX0iRClxu4dEUg8Bs2pNnr6huY2Ft+qb41RzCJvvMyu gS32LfN0bTZ6Qm2A8ayMtUQgnwZDSO23OKgQWZVglGliY3ezHZ6lVwC24Vjkmq/2yBSLakZE 6DZUjZzCW1nvtRK05ebyK6tofRsx8xB8pL/kcBb9nCuh70aLR+5cmE41X4O+MVJbwfP5s/RW 9BFSL3qgXuXso/3XuWTQjJJGgKhB6xXjMmb1J4q/h5IuVV4juv1Fem9sfmyrh+Wi5V1IzKI7 RPJ3KVb937eBgSENk53P0gUorwzUcO+ASEo3Z1cBKkJSPigDbeEjVfXQMzNt0oDRzpQqH2vp apo2jHnidWt8BsckuWZpxcZ9+/9obQ55DyVQHGiTN39hkETy3Emdnz1JVHTU0Q== Message-ID: <933eea5f-137b-a537-8165-6b5a4896aecd@redhat.com> Date: Wed, 16 Sep 2020 12:17:52 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200916093133.GA749356@stefanha-x1.localdomain> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8bit Content-Language: en-US Received-SPF: pass client-ip=216.205.24.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/16 02:16:02 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -50 X-Spam_score: -5.1 X-Spam_bar: ----- X-Spam_report: (-5.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.999, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Xiao Guangrong , "Michael S. Tsirkin" , Julio Montes , qemu-devel@nongnu.org, Igor Mammedov , Paolo Bonzini , Richard Henderson , Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 9/16/20 11:31 AM, Stefan Hajnoczi wrote: > On Fri, Aug 21, 2020 at 02:50:42PM +0200, Philippe Mathieu-Daudé wrote: >> On 8/4/20 12:12 PM, Stefan Hajnoczi wrote: >>> Let -object memory-backend-file work on read-only files when the >>> readonly=on option is given. This can be used to share the contents of a >>> file between multiple guests while preventing them from consuming >>> Copy-on-Write memory if guests dirty the pages, for example. >>> [...] >>> +static bool file_memory_backend_get_readonly(Object *o, Error **errp) >>> +{ >>> + return MEMORY_BACKEND_FILE(o)->readonly; >>> +} >>> + >>> +static void file_memory_backend_set_readonly(Object *o, bool value, >>> + Error **errp) >>> +{ >>> + HostMemoryBackend *backend = MEMORY_BACKEND(o); >>> + HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o); >>> + >>> + if (host_memory_backend_mr_inited(backend)) { >>> + error_setg(errp, "cannot change property 'readonly' of %s.", >>> + object_get_typename(o)); >> >> >> The 'host_memory_backend_mr_inited()' function is not documented; >> my understanding is a backend is considered initialized once it has >> a MemoryRegion assigned to it. >> >> So this error message is not very helpful, it doesn't explain the >> reason. I see all other setters in this file use the same error, >> so it is almost a predating issue. >> >> Still I'd rather use a different message, something like: >> "'%s' already initialized, can not set it 'readonly'". >> >> Preferably with the error message reworded: >> Reviewed-by: Philippe Mathieu-Daudé > > I haven't reworded the error message because it's used in > hostmem-file.c, hostmem-memfd.c, and hostmem.c. A separate patch would > need to change the error messages across these files. > > There is no time when users can actually change these QOM properties, so > "cannot change FOO" is a reasonable wording form the user perspective. > Telling the user that there is a pre-initialization state when the > property can be change isn't useful because they cannot observe that > state (the object is created and ->complete is called in a single step). OK, understood.