diff options
Diffstat (limited to 'include/uapi/xen/gntdev.h')
| -rw-r--r-- | include/uapi/xen/gntdev.h | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/include/uapi/xen/gntdev.h b/include/uapi/xen/gntdev.h index 9ac5515b9bc2..7a7145395c09 100644 --- a/include/uapi/xen/gntdev.h +++ b/include/uapi/xen/gntdev.h @@ -47,7 +47,13 @@ struct ioctl_gntdev_grant_ref { /* * Inserts the grant references into the mapping table of an instance * of gntdev. N.B. This does not perform the mapping, which is deferred - * until mmap() is called with @index as the offset. + * until mmap() is called with @index as the offset. @index should be + * considered opaque to userspace, with one exception: if no grant + * references have ever been inserted into the mapping table of this + * instance, @index will be set to 0. This is necessary to use gntdev + * with userspace APIs that expect a file descriptor that can be + * mmap()'d at offset 0, such as Wayland. If @count is set to 0, this + * ioctl will fail. */ #define IOCTL_GNTDEV_MAP_GRANT_REF \ _IOC(_IOC_NONE, 'G', 0, sizeof(struct ioctl_gntdev_map_grant_ref)) |