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| author | Michael S. Tsirkin <mst@redhat.com> | 2014-12-25 17:03:27 +0300 |
|---|---|---|
| committer | Michael S. Tsirkin <mst@redhat.com> | 2014-12-29 11:54:54 +0300 |
| commit | b28e0506fafd9c987bba7a6a71ea02a37fcabdea (patch) | |
| tree | d106164f315a92e8894454fdf93226bff5f53d3e | |
| parent | b7392d2247cfe6771f95d256374f1a8e6a6f48d6 (diff) | |
| download | linux-b28e0506fafd9c987bba7a6a71ea02a37fcabdea.tar.xz | |
virtio_ring: document alignment requirements
Host needs to know vring element alignment requirements:
simply doing alignof on structures doesn't work reliably: on some
platforms gcc has alignof(uint32_t) == 2.
Add macros for alignment as specified in virtio 1.0 cs01,
export them to userspace as well.
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
| -rw-r--r-- | include/uapi/linux/virtio_ring.h | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h index 61c818a7fe70..a3318f31e8e7 100644 --- a/include/uapi/linux/virtio_ring.h +++ b/include/uapi/linux/virtio_ring.h @@ -101,6 +101,13 @@ struct vring { struct vring_used *used; }; +/* Alignment requirements for vring elements. + * When using pre-virtio 1.0 layout, these fall out naturally. + */ +#define VRING_AVAIL_ALIGN_SIZE 2 +#define VRING_USED_ALIGN_SIZE 4 +#define VRING_DESC_ALIGN_SIZE 16 + /* The standard layout for the ring is a continuous chunk of memory which looks * like this. We assume num is a power of 2. * |