Re: [PATCH v2 4/7] virtio: VIRTIO_DEVICE_F_MASK for all per-device features
From: Si-Wei Liu
Date: Thu Feb 02 2023 - 17:22:20 EST
On 2/2/2023 9:29 AM, Michael S. Tsirkin wrote:
On Tue, Jan 31, 2023 at 03:22:22PM -0800, Si-Wei Liu wrote:
Introduce VIRTIO_DEVICE_F_MASK bitmask used for identification
of per-device features. Feature bits VIRTIO_TRANSPORT_F_START
through VIRTIO_TRANSPORT_F_END are reserved for transport
features hence are not counted as per-device features against
the 64bit feature space.
Signed-off-by: Si-Wei Liu <si-wei.liu@xxxxxxxxxx>
---
include/uapi/linux/virtio_config.h | 8 ++++++++
1 file changed, 8 insertions(+)
Pls don't add this in uapi, people tend to depend on this and then
things fail when we extend virtio. For example this won't work with >64
feature bits.
Good point. Then keep this macro private to vdpa.c for now?
-Siwei
diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
index 3c05162..3bdc7ed 100644
--- a/include/uapi/linux/virtio_config.h
+++ b/include/uapi/linux/virtio_config.h
@@ -54,6 +54,14 @@
#define VIRTIO_TRANSPORT_F_START 28
#define VIRTIO_TRANSPORT_F_END 41
+/*
+ * Bitmask for all per-device features: feature bits VIRTIO_TRANSPORT_F_START
+ * through VIRTIO_TRANSPORT_F_END are unset, i.e. 0xfffffc000fffffff for
+ * all 64bit features
+ */
+#define VIRTIO_DEVICE_F_MASK (~0ULL << (VIRTIO_TRANSPORT_F_END + 1) | \
+ ((1ULL << VIRTIO_TRANSPORT_F_START) - 1))
+
#ifndef VIRTIO_CONFIG_NO_LEGACY
/* Do we get callbacks when the ring is completely used, even if we've
* suppressed them? */
--
1.8.3.1