linux-kernel - [PATCH] vfio: return -ENOTTY for unsupported device feature

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Message-ID: <20250908-vfio-enotty-v1-1-4428e1539e2e@fb.com>
Date: Mon, 8 Sep 2025 08:58:40 -0700
From: Alex Mastro <amastro@...com>
To: Alex Williamson <alex.williamson@...hat.com>
CC: Jason Gunthorpe <jgg@...pe.ca>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Alex Mastro <amastro@...com>
Subject: [PATCH] vfio: return -ENOTTY for unsupported device feature

The two implementers of vfio_device_ops.device_feature,
vfio_cdx_ioctl_feature and vfio_pci_core_ioctl_feature, return
-ENOTTY in the fallthrough case when the feature is unsupported. For
consistency, the base case, vfio_ioctl_device_feature, should do the
same when device_feature == NULL, indicating an implementation has no
feature extensions.

Signed-off-by: Alex Mastro <amastro@...com>
---
The commit message makes the main points, but I'm assuming that it was
intended for ENOTTY and not EINVAL to be the errno to indicate "this
feature is not supported".
---
 drivers/vfio/vfio_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 91a8eae308ea..38c8e9350a60 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -1252,7 +1252,7 @@ static int vfio_ioctl_device_feature(struct vfio_device *device,
 			feature.argsz - minsz);
 	default:
 		if (unlikely(!device->ops->device_feature))
-			return -EINVAL;
+			return -ENOTTY;
 		return device->ops->device_feature(device, feature.flags,
 						   arg->data,
 						   feature.argsz - minsz);

---
base-commit: 093458c58f830d0a713fab0de037df5f0ce24fef
change-id: 20250907-vfio-enotty-69f892c33efe

Best regards,
-- 
Alex Mastro <amastro@...com>