{"id":2221391,"url":"http://patchwork.ozlabs.org/api/1.2/patches/2221391/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260409114312.1704062-1-clg@redhat.com/","project":{"id":14,"url":"http://patchwork.ozlabs.org/api/1.2/projects/14/?format=json","name":"QEMU Development","link_name":"qemu-devel","list_id":"qemu-devel.nongnu.org","list_email":"qemu-devel@nongnu.org","web_url":"","scm_url":"","webscm_url":"","list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"<20260409114312.1704062-1-clg@redhat.com>","list_archive_url":null,"date":"2026-04-09T11:43:12","name":"vfio: Add VFIO I/O backend capability flags for feature support","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"e46c5336dc1a6dc746d876eefbdf9dbf1f7206bc","submitter":{"id":85406,"url":"http://patchwork.ozlabs.org/api/1.2/people/85406/?format=json","name":"Cédric Le Goater","email":"clg@redhat.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260409114312.1704062-1-clg@redhat.com/mbox/","series":[{"id":499280,"url":"http://patchwork.ozlabs.org/api/1.2/series/499280/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/list/?series=499280","date":"2026-04-09T11:43:12","name":"vfio: Add VFIO I/O backend capability flags for feature support","version":1,"mbox":"http://patchwork.ozlabs.org/series/499280/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2221391/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2221391/checks/","tags":{},"related":[],"headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=b13T5D8F;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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Thu, 09 Apr 2026 07:43:23 -0400","from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com\n (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by\n relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3,\n cipher=TLS_AES_256_GCM_SHA384) id us-mta-515-dccb79HSMQyTRS7AZAwb4A-1; Thu,\n 09 Apr 2026 07:43:18 -0400","from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com\n (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93])\n (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest\n SHA256)\n (No client certificate requested)\n by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS\n id 3996119560A3; Thu, 9 Apr 2026 11:43:17 +0000 (UTC)","from corto.redhat.com (unknown [10.44.32.21])\n by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP\n id 4F81E180036E; Thu, 9 Apr 2026 11:43:14 +0000 (UTC)"],"DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;\n s=mimecast20190719; t=1775735000;\n h=from:from:reply-to:subject:subject:date:date:message-id:message-id:\n to:to:cc:cc:mime-version:mime-version:content-type:content-type:\n content-transfer-encoding:content-transfer-encoding;\n bh=aEZhY1E5eo7lYxSjD0EwAhHg/UAubLjLjd8ZdBwDe8w=;\n b=b13T5D8FLuN8GZbxbSeq2JcT+e8KEklCrumrCubHjvLir3u6UHbjcKnlwmIV2OmyKFaG1n\n ZXBzS8c6DYvcEJxSsZ+yl26Z6wZj7BkO/yFGbz2qC6AOZKOw3wtJXFAHYgPwSWlP8GCQ6C\n FzrgzDgfaaXyB2fwCK27pZ3fwCUJrqg=","X-MC-Unique":"dccb79HSMQyTRS7AZAwb4A-1","X-Mimecast-MFC-AGG-ID":"dccb79HSMQyTRS7AZAwb4A_1775734997","From":"=?utf-8?q?C=C3=A9dric_Le_Goater?= ","To":"qemu-devel@nongnu.org","Cc":"Alex Williamson ,\n =?utf-8?q?C=C3=A9dric_Le_Goater?= ,\n John Levon ","Subject":"[PATCH] vfio: Add VFIO I/O backend capability flags for feature\n support","Date":"Thu, 9 Apr 2026 13:43:12 +0200","Message-ID":"<20260409114312.1704062-1-clg@redhat.com>","MIME-Version":"1.0","Content-Type":"text/plain; charset=UTF-8","Content-Transfer-Encoding":"8bit","X-Scanned-By":"MIMEDefang 3.4.1 on 10.30.177.93","Received-SPF":"pass client-ip=170.10.129.124; envelope-from=clg@redhat.com;\n helo=us-smtp-delivery-124.mimecast.com","X-Spam_score_int":"7","X-Spam_score":"0.7","X-Spam_bar":"/","X-Spam_report":"(0.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.54,\n DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001,\n RCVD_IN_SBL_CSS=3.335, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001,\n RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001,\n SPF_PASS=-0.001 autolearn=no autolearn_force=no","X-Spam_action":"no action","X-BeenThere":"qemu-devel@nongnu.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"qemu development ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org"},"content":"Different VFIO I/O backends support different features. For example,\nthe kernel VFIO backend supports DMA-BUF creation, while vfio-user\ndoes not. Currently, this is handled by attempting the operation and\nchecking for -ENOTTY, which can lead to misleading warnings when a\nfeature is simply not supported by a particular backend.\n\nIntroduce a capability flags mechanism in VFIODeviceIOOps that allows\nbackends to explicitly advertise which features they support. Callers\ncan check these capabilities before attempting operations, avoiding\nspurious errors and warnings.\n\nCc: John Levon \nSigned-off-by: Cédric Le Goater \n---\n include/hw/vfio/vfio-device.h | 13 +++++++++++++\n hw/vfio/device.c | 2 ++\n hw/vfio/region.c | 5 +++++\n 3 files changed, 20 insertions(+)","diff":"diff --git a/include/hw/vfio/vfio-device.h b/include/hw/vfio/vfio-device.h\nindex a95c5bf50302a7394582dcc493d96aef00b47dc8..380a55d6e5ea280c8f44016c7a8a1dcb8f4c00fe 100644\n--- a/include/hw/vfio/vfio-device.h\n+++ b/include/hw/vfio/vfio-device.h\n@@ -172,12 +172,25 @@ typedef QLIST_HEAD(VFIODeviceList, VFIODevice) VFIODeviceList;\n extern VFIODeviceList vfio_device_list;\n \n #ifdef CONFIG_LINUX\n+/*\n+ * VFIO backend I/O operation capabilities\n+ */\n+#define VFIO_IO_CAP_DMA_BUF (1ULL << 0)\n+\n /*\n * How devices communicate with the server. The default option is through\n * ioctl() to the kernel VFIO driver, but vfio-user can use a socket to a remote\n * process.\n */\n struct VFIODeviceIOOps {\n+ /**\n+ * @capabilities\n+ *\n+ * Bitmask of VFIO_IO_CAP_* flags indicating which features this\n+ * backend supports.\n+ */\n+ uint64_t capabilities;\n+\n /**\n * @device_feature\n *\ndiff --git a/hw/vfio/device.c b/hw/vfio/device.c\nindex 8f7ae919a55dd9e08bdd072eee33f5b46a91aa2a..3ffd69a579b8ac135ef729d3d836c8545e36786b 100644\n--- a/hw/vfio/device.c\n+++ b/hw/vfio/device.c\n@@ -648,6 +648,8 @@ static int vfio_device_io_region_write(VFIODevice *vbasedev, uint8_t index,\n }\n \n static VFIODeviceIOOps vfio_device_io_ops_ioctl = {\n+ .capabilities = VFIO_IO_CAP_DMA_BUF,\n+\n .device_feature = vfio_device_io_device_feature,\n .get_region_info = vfio_device_io_get_region_info,\n .get_irq_info = vfio_device_io_get_irq_info,\ndiff --git a/hw/vfio/region.c b/hw/vfio/region.c\nindex 47fdc2df349b65c6be6c9605b7a38a4e367f0475..0342ca712acd0ad846685115c29432c15aa966a0 100644\n--- a/hw/vfio/region.c\n+++ b/hw/vfio/region.c\n@@ -293,6 +293,11 @@ static bool vfio_region_create_dma_buf(VFIORegion *region, Error **errp)\n size_t total_size;\n int i, ret;\n \n+ /* Check if backend supports DMA-BUF creation */\n+ if (!(vbasedev->io_ops->capabilities & VFIO_IO_CAP_DMA_BUF)) {\n+ return true;\n+ }\n+\n total_size = sizeof(*feature) + sizeof(*dma_buf) +\n sizeof(struct vfio_region_dma_range) * region->nr_mmaps;\n feature = g_malloc0(total_size);\n","prefixes":[]}