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(p200300cbc7087900b88ec72aabbdd3d9.dip0.t-ipconnect.de. [2003:cb:c708:7900:b88e:c72a:abbd:d3d9]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-432b05c1f56sm29429455e9.34.2024.11.07.08.19.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 Nov 2024 08:19:19 -0800 (PST) Message-ID: <715ddc40-dbce-434d-ab2c-4d4424561f37@redhat.com> Date: Thu, 7 Nov 2024 17:19:18 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V3 01/16] machine: anon-alloc option To: Steven Sistare , Peter Xu Cc: Fabiano Rosas , Marcel Apfelbaum , Eduardo Habkost , Philippe Mathieu-Daude , Paolo Bonzini , "Daniel P. Berrange" , Markus Armbruster , qemu-devel@nongnu.org References: <1730468875-249970-1-git-send-email-steven.sistare@oracle.com> <1730468875-249970-2-git-send-email-steven.sistare@oracle.com> <78fa25f1-03dc-400c-a604-998c53e4fbce@redhat.com> <45ea8a8a-928d-4703-b698-d5f910e6a224@oracle.com> <1f1a2742-0429-47d5-958f-b37575c1e4ba@redhat.com> <09701693-436c-4e1a-8206-03eb26cacab5@redhat.com> <66c05a06-dbb7-49ec-b58e-ccd917d098ea@oracle.com> <7fb32744-0512-46e2-b58d-2990f742b897@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.34, 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, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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 On 07.11.24 15:04, Steven Sistare wrote: > On 11/7/2024 8:05 AM, David Hildenbrand wrote: >> On 06.11.24 21:59, Steven Sistare wrote: >>> On 11/6/2024 3:41 PM, Peter Xu wrote: >>>> On Wed, Nov 06, 2024 at 03:12:20PM -0500, Steven Sistare wrote: >>>>> On 11/4/2024 4:36 PM, David Hildenbrand wrote: >>>>>> On 04.11.24 21:56, Steven Sistare wrote: >>>>>>> On 11/4/2024 3:15 PM, David Hildenbrand wrote: >>>>>>>> On 04.11.24 20:51, David Hildenbrand wrote: >>>>>>>>> On 04.11.24 18:38, Steven Sistare wrote: >>>>>>>>>> On 11/4/2024 5:39 AM, David Hildenbrand wrote: >>>>>>>>>>> On 01.11.24 14:47, Steve Sistare wrote: >>>>>>>>>>>> Allocate anonymous memory using mmap MAP_ANON or memfd_create depending >>>>>>>>>>>> on the value of the anon-alloc machine property.  This option applies to >>>>>>>>>>>> memory allocated as a side effect of creating various devices. It does >>>>>>>>>>>> not apply to memory-backend-objects, whether explicitly specified on >>>>>>>>>>>> the command line, or implicitly created by the -m command line option. >>>>>>>>>>>> >>>>>>>>>>>> The memfd option is intended to support new migration modes, in which the >>>>>>>>>>>> memory region can be transferred in place to a new QEMU process, by sending >>>>>>>>>>>> the memfd file descriptor to the process.  Memory contents are preserved, >>>>>>>>>>>> and if the mode also transfers device descriptors, then pages that are >>>>>>>>>>>> locked in memory for DMA remain locked.  This behavior is a pre-requisite >>>>>>>>>>>> for supporting vfio, vdpa, and iommufd devices with the new modes. >>>>>>>>>>> >>>>>>>>>>> A more portable, non-Linux specific variant of this will be using shm, >>>>>>>>>>> similar to backends/hostmem-shm.c. >>>>>>>>>>> >>>>>>>>>>> Likely we should be using that instead of memfd, or try hiding the >>>>>>>>>>> details. See below. >>>>>>>>>> >>>>>>>>>> For this series I would prefer to use memfd and hide the details.  It's a >>>>>>>>>> concise (and well tested) solution albeit linux only.  The code you supply >>>>>>>>>> for posix shm would be a good follow on patch to support other unices. >>>>>>>>> >>>>>>>>> Unless there is reason to use memfd we should start with the more >>>>>>>>> generic POSIX variant that is available even on systems without memfd. >>>>>>>>> Factoring stuff out as I drafted does look quite compelling. >>>>>>>>> >>>>>>>>> I can help with the rework, and send it out separately, so you can focus >>>>>>>>> on the "machine toggle" as part of this series. >>>>>>>>> >>>>>>>>> Of course, if we find out we need the memfd internally instead under >>>>>>>>> Linux for whatever reason later, we can use that instead. >>>>>>>>> >>>>>>>>> But IIUC, the main selling point for memfd are additional features >>>>>>>>> (hugetlb, memory sealing) that you aren't even using. >>>>>>>> >>>>>>>> FWIW, I'm looking into some details, and one difference is that shmem_open() under Linux (glibc) seems to go to /dev/shmem and memfd/SYSV go to the internal tmpfs mount. There is not a big difference, but there can be some difference (e.g., sizing of the /dev/shm mount). >>>>>>> >>>>>>> Sizing is a non-trivial difference.  One can by default allocate all memory using memfd_create. >>>>>>> To do so using shm_open requires configuration on the mount.  One step harder to use. >>>>>> >>>>>> Yes. >>>>>> >>>>>>> >>>>>>> This is a real issue for memory-backend-ram, and becomes an issue for the internal RAM >>>>>>> if memory-backend-ram has hogged all the memory. >>>>>>> >>>>>>>> Regarding memory-backend-ram,share=on, I assume we can use memfd if available, but then fallback to shm_open(). >>>>>>> >>>>>>> Yes, and if that is a good idea, then the same should be done for internal RAM >>>>>>> -- memfd if available and fallback to shm_open. >>>>>> >>>>>> Yes. >>>>>> >>>>>>> >>>>>>>> I'm hoping we can find a way where it just all is rather intuitive, like >>>>>>>> >>>>>>>> "default-ram-share=on": behave for internal RAM just like "memory-backend-ram,share=on" >>>>>>>> >>>>>>>> "memory-backend-ram,share=on": use whatever mechanism we have to give us "anonymous" memory that can be shared using an fd with another process. >>>>>>>> >>>>>>>> Thoughts? >>>>>>> >>>>>>> Agreed, though I thought I had already landed at the intuitive specification in my patch. >>>>>>> The user must explicitly configure memory-backend-* to be usable with CPR, and anon-alloc >>>>>>> controls everything else.  Now we're just riffing on the details: memfd vs shm_open, spelling >>>>>>> of options and words to describe them. >>>>>> >>>>>> Well, yes, and making it all a bit more consistent and the "machine option" behave just like "memory-backend-ram,share=on". >>>>> >>>>> Hi David and Peter, >>>>> >>>>> I have implemented and tested the following, for both qemu_memfd_create >>>>> and qemu_shm_alloc.  This is pseudo-code, with error conditions omitted >>>>> for simplicity. >>>> >>>> I'm ok with either shm or memfd, as this feature only applies to Linux >>>> anyway.  I'll leave that part to you and David to decide. >>>> >>>>> >>>>> Any comments before I submit a complete patch? >>>>> >>>>> ---- >>>>> qemu-options.hx: >>>>>       ``aux-ram-share=on|off`` >>>>>           Allocate auxiliary guest RAM as an anonymous file that is >>>>>           shareable with an external process.  This option applies to >>>>>           memory allocated as a side effect of creating various devices. >>>>>           It does not apply to memory-backend-objects, whether explicitly >>>>>           specified on the command line, or implicitly created by the -m >>>>>           command line option. >>>>> >>>>>           Some migration modes require aux-ram-share=on. >>>>> >>>>> qapi/migration.json: >>>>>       @cpr-transfer: >>>>>            ... >>>>>            Memory-backend objects must have the share=on attribute, but >>>>>            memory-backend-epc is not supported.  The VM must be started >>>>>            with the '-machine aux-ram-share=on' option. >>>>> >>>>> Define RAM_PRIVATE >>>>> >>>>> Define qemu_shm_alloc(), from David's tmp patch >>>>> >>>>> ram_backend_memory_alloc() >>>>>       ram_flags = backend->share ? RAM_SHARED : RAM_PRIVATE; >>>>>       memory_region_init_ram_flags_nomigrate(ram_flags) >>>> >>>> Looks all good until here. >>>> >>>>> >>>>> qemu_ram_alloc_internal() >>>>>       ... >>>>>       if (!host && !(ram_flags & RAM_PRIVATE) && current_machine->aux_ram_share) >>>> >>>> Nitpick: could rely on flags-only, rather than testing "!host", AFAICT >>>> that's equal to RAM_PREALLOC. >>> >>> IMO testing host is clearer and more future proof, regardless of how flags >>> are currently used.  If the caller passes host, then we should not allocate >>> memory here, full stop. >>> >>>> Meanwhile I slightly prefer we don't touch >>>> anything if SHARED|PRIVATE is set. >>> >>> OK, if SHARED is already set I will not set it again. >> >> We only have to make sure that stuff like qemu_ram_is_shared() will continue working as expected. >> >> What I think we should do: >> >> We should probably assert that nobody passes in SHARED|PRIVATE. And we can use PRIVATE only as a parameter to the function, but never actually set it on the ramblock. >> >> If someone passes in PRIVATE, we don't include it in block->flags. (RMA_SHARED remains cleared) >> >> If someone passes in SHARED, we do set it in block->flags. >> If someone passes PRIVATE|SHARED, we assert. >> >> If someone passes in nothing: we set block->flags to SHARED with aux_ram_share=on. Otherwise, we do nothing (RAM_SHARED remains cleared) >> >> If that's also what you had in mind, great. > > Yes, my patch does that, but it also sets RAM_PRIVATE on the ramblock. > I will undo the latter. > > Do you plan to submit the part of your "tmp" patch that refactors > shm_backend_memory_alloc and defines qemu_shm_alloc? If you want, > I could include it in my series, with your Signed-off-by. My patch went a bit too far I think. And would not work on win32 :) We should probably start with this: From 124920aeda2756faa104bfa6e934c7c20b1fbbe9 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Mon, 4 Nov 2024 11:29:22 +0100 Subject: [PATCH] backends/hostmem-shm: factor out allocation of "anonymous shared memory with an fd" Let's factor it out so we can reuse it. Signed-off-by: David Hildenbrand --- backends/hostmem-shm.c | 45 ++++------------------------------- include/qemu/osdep.h | 1 + system/physmem.c | 2 +- util/oslib-posix.c | 53 ++++++++++++++++++++++++++++++++++++++++++ util/oslib-win32.c | 6 +++++ 5 files changed, 65 insertions(+), 42 deletions(-) diff --git a/backends/hostmem-shm.c b/backends/hostmem-shm.c index 374edc3db8..837b9f1dd4 100644 --- a/backends/hostmem-shm.c +++ b/backends/hostmem-shm.c @@ -25,11 +25,9 @@ struct HostMemoryBackendShm { static bool shm_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) { - g_autoptr(GString) shm_name = g_string_new(NULL); g_autofree char *backend_name = NULL; uint32_t ram_flags; - int fd, oflag; - mode_t mode; + int fd; if (!backend->size) { error_setg(errp, "can't create shm backend with size 0"); @@ -41,48 +39,13 @@ shm_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) return false; } - /* - * Let's use `mode = 0` because we don't want other processes to open our - * memory unless we share the file descriptor with them. - */ - mode = 0; - oflag = O_RDWR | O_CREAT | O_EXCL; - backend_name = host_memory_backend_get_name(backend); - - /* - * Some operating systems allow creating anonymous POSIX shared memory - * objects (e.g. FreeBSD provides the SHM_ANON constant), but this is not - * defined by POSIX, so let's create a unique name. - * - * From Linux's shm_open(3) man-page: - * For portable use, a shared memory object should be identified - * by a name of the form /somename;" - */ - g_string_printf(shm_name, "/qemu-" FMT_pid "-shm-%s", getpid(), - backend_name); - - fd = shm_open(shm_name->str, oflag, mode); + fd = qemu_shm_alloc(backend->size, errp); if (fd < 0) { - error_setg_errno(errp, errno, - "failed to create POSIX shared memory"); - return false; - } - - /* - * We have the file descriptor, so we no longer need to expose the - * POSIX shared memory object. However it will remain allocated as long as - * there are file descriptors pointing to it. - */ - shm_unlink(shm_name->str); - - if (ftruncate(fd, backend->size) == -1) { - error_setg_errno(errp, errno, - "failed to resize POSIX shared memory to %" PRIu64, - backend->size); - close(fd); return false; } + /* Let's do the same as memory-backend-ram,share=on would do. */ + backend_name = host_memory_backend_get_name(backend); ram_flags = RAM_SHARED; ram_flags |= backend->reserve ? 0 : RAM_NORESERVE; diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h index fe7c3c5f67..4a24f11174 100644 --- a/include/qemu/osdep.h +++ b/include/qemu/osdep.h @@ -505,6 +505,7 @@ int qemu_daemon(int nochdir, int noclose); void *qemu_anon_ram_alloc(size_t size, uint64_t *align, bool shared, bool noreserve); void qemu_anon_ram_free(void *ptr, size_t size); +int qemu_shm_alloc(size_t size, Error **errp); #ifdef _WIN32 #define HAVE_CHARDEV_SERIAL 1 diff --git a/system/physmem.c b/system/physmem.c index dc1db3a384..1b477fec44 100644 --- a/system/physmem.c +++ b/system/physmem.c @@ -2089,7 +2089,7 @@ RAMBlock *qemu_ram_alloc_internal(ram_addr_t size, ram_addr_t max_size, new_block->page_size = qemu_real_host_page_size(); new_block->host = host; new_block->flags = ram_flags; - ram_block_add(new_block, &local_err); + if (local_err) { g_free(new_block); error_propagate(errp, local_err); diff --git a/util/oslib-posix.c b/util/oslib-posix.c index 11b35e48fb..bc5c28b162 100644 --- a/util/oslib-posix.c +++ b/util/oslib-posix.c @@ -931,3 +931,56 @@ void qemu_close_all_open_fd(const int *skip, unsigned int nskip) qemu_close_all_open_fd_fallback(skip, nskip, open_max); } } + +int qemu_shm_alloc(size_t size, Error **errp) +{ + g_autoptr(GString) shm_name = g_string_new(NULL); + int fd, oflag, cur_sequence; + static int sequence; + mode_t mode; + + cur_sequence = qatomic_fetch_inc(&sequence); + + /* + * Let's use `mode = 0` because we don't want other processes to open our + * memory unless we share the file descriptor with them. + */ + mode = 0; + oflag = O_RDWR | O_CREAT | O_EXCL; + + /* + * Some operating systems allow creating anonymous POSIX shared memory + * objects (e.g. FreeBSD provides the SHM_ANON constant), but this is not + * defined by POSIX, so let's create a unique name. + * + * From Linux's shm_open(3) man-page: + * For portable use, a shared memory object should be identified + * by a name of the form /somename;" + */ + g_string_printf(shm_name, "/qemu-" FMT_pid "-shm-%d", getpid(), + cur_sequence); + + fd = shm_open(shm_name->str, oflag, mode); + if (fd < 0) { + error_setg_errno(errp, errno, + "failed to create POSIX shared memory"); + return -1; + } + + /* + * We have the file descriptor, so we no longer need to expose the + * POSIX shared memory object. However it will remain allocated as long as + * there are file descriptors pointing to it. + */ + shm_unlink(shm_name->str); + + if (ftruncate(fd, size) == -1) { + error_setg_errno(errp, errno, + "failed to resize POSIX shared memory to %" PRIu64, + size); + close(fd); + return -1; + } + + return fd; +} diff --git a/util/oslib-win32.c b/util/oslib-win32.c index b623830d62..f79a190b78 100644 --- a/util/oslib-win32.c +++ b/util/oslib-win32.c @@ -877,3 +877,9 @@ void qemu_win32_map_free(void *ptr, HANDLE h, Error **errp) } CloseHandle(h); } + +int qemu_shm_alloc(size_t size, Error **errp) +{ + error_setg("Shared memory is not supported."); + return -1; +} -- 2.47.0 So we can reuse it for the !host && RAM_SHARED case. > > Do you have any comments on my proposed name aux-ram-share, or my proposed text aux-ram-share works for me, I prefer "aux" over the "default" I had in mind. > for qemu-options.hx and migration.json? Speaking now would prevent more version > churn later. Both sounds good to me after a quick scan. -- Cheers, David / dhildenb