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Berrange" , Eric Blake , "Philippe Mathieu-Daude" , Peter Xu , "Paolo Bonzini" , Igor Mammedov , "Stefan Hajnoczi" , Ashish Kalra , "Tom Lendacky" Subject: Re: [PATCH v2] hostmem-file: add offset option References: <20230401121316.2025-1-graf@amazon.com> Date: Mon, 03 Apr 2023 08:28:21 +0200 In-Reply-To: <20230401121316.2025-1-graf@amazon.com> (Alexander Graf's message of "Sat, 1 Apr 2023 12:13:16 +0000") Message-ID: <87wn2tjx8a.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Alexander Graf writes: > Add an option for hostmem-file to start the memory object at an offset > into the target file. This is useful if multiple memory objects reside > inside the same target file, such as a device node. > > In particular, it's useful to map guest memory directly into /dev/mem > for experimentation. > > Signed-off-by: Alexander Graf [...] > diff --git a/qapi/qom.json b/qapi/qom.json > index a877b879b9..8f5eaa8415 100644 > --- a/qapi/qom.json > +++ b/qapi/qom.json > @@ -635,6 +635,10 @@ > # specify the required alignment via this option. > # 0 selects a default alignment (currently the page size). (default: 0) > # > +# @offset: the offset into the target file that the region starts at. You can > +# use this option to overload multiple regions into a single fils. single file I'm not sure about "to overload multiple regions into a single file". Maybe "to back multiple regions with a single file". Any alignment requirements? What happens when the regions overlap? > +# (default: 0) (since 8.1) > +# > # @discard-data: if true, the file contents can be destroyed when QEMU exits, > # to avoid unnecessarily flushing data to the backing file. Note > # that ``discard-data`` is only an optimization, and QEMU might > @@ -655,6 +659,7 @@ > { 'struct': 'MemoryBackendFileProperties', > 'base': 'MemoryBackendProperties', > 'data': { '*align': 'size', > + '*offset': 'size', > '*discard-data': 'bool', > 'mem-path': 'str', > '*pmem': { 'type': 'bool', 'if': 'CONFIG_LIBPMEM' }, [...]