From bbff2f321a864ee07c9d3d1245af498023146951 Mon Sep 17 00:00:00 2001 From: Björn Töpel Date: Mon, 4 Jun 2018 13:57:13 +0200 Subject: xsk: new descriptor addressing scheme Currently, AF_XDP only supports a fixed frame-size memory scheme where each frame is referenced via an index (idx). A user passes the frame index to the kernel, and the kernel acts upon the data. Some NICs, however, do not have a fixed frame-size model, instead they have a model where a memory window is passed to the hardware and multiple frames are filled into that window (referred to as the "type-writer" model). By changing the descriptor format from the current frame index addressing scheme, AF_XDP can in the future be extended to support these kinds of NICs. In the index-based model, an idx refers to a frame of size frame_size. Addressing a frame in the UMEM is done by offseting the UMEM starting address by a global offset, idx * frame_size + offset. Communicating via the fill- and completion-rings are done by means of idx. In this commit, the idx is removed in favor of an address (addr), which is a relative address ranging over the UMEM. To convert an idx-based address to the new addr is simply: addr = idx * frame_size + offset. We also stop referring to the UMEM "frame" as a frame. Instead it is simply called a chunk. To transfer ownership of a chunk to the kernel, the addr of the chunk is passed in the fill-ring. Note, that the kernel will mask addr to make it chunk aligned, so there is no need for userspace to do that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or 3000 to the fill-ring will refer to the same chunk. On the completion-ring, the addr will match that of the Tx descriptor, passed to the kernel. Changing the descriptor format to use chunks/addr will allow for future changes to move to a type-writer based model, where multiple frames can reside in one chunk. In this model passing one single chunk into the fill-ring, would potentially result in multiple Rx descriptors. This commit changes the uapi of AF_XDP sockets, and updates the documentation. Signed-off-by: Björn Töpel Signed-off-by: Daniel Borkmann --- include/uapi/linux/if_xdp.h | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) (limited to 'include/uapi') diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h index 4737cfe222f5..e411d6f9ac65 100644 --- a/include/uapi/linux/if_xdp.h +++ b/include/uapi/linux/if_xdp.h @@ -48,8 +48,8 @@ struct xdp_mmap_offsets { struct xdp_umem_reg { __u64 addr; /* Start of packet data area */ __u64 len; /* Length of packet data area */ - __u32 frame_size; /* Frame size */ - __u32 frame_headroom; /* Frame head room */ + __u32 chunk_size; + __u32 headroom; }; struct xdp_statistics { @@ -66,13 +66,11 @@ struct xdp_statistics { /* Rx/Tx descriptor */ struct xdp_desc { - __u32 idx; + __u64 addr; __u32 len; - __u16 offset; - __u8 flags; - __u8 padding[5]; + __u32 options; }; -/* UMEM descriptor is __u32 */ +/* UMEM descriptor is __u64 */ #endif /* _LINUX_IF_XDP_H */ -- cgit v1.2.3-55-g7522