Date:   Tue, 29 Jan 2019 16:12:14 +0100
From:   Magnus Karlsson <magnus.karlsson@...el.com>
To:     magnus.karlsson@...el.com, bjorn.topel@...el.com, ast@...nel.org,
        daniel@...earbox.net, netdev@...r.kernel.org,
        jakub.kicinski@...ronome.com, bjorn.topel@...il.com,
        qi.z.zhang@...el.com
Cc:     brouer@...hat.com
Subject: [PATCH bpf-next v3 0/3] libbpf: adding AF_XDP support

This patch proposes to add AF_XDP support to libbpf. The main reason
for this is to facilitate writing applications that use AF_XDP by
offering higher-level APIs that hide many of the details of the AF_XDP
uapi. This is in the same vein as libbpf facilitates XDP adoption by
offering easy-to-use higher level interfaces of XDP
functionality. Hopefully this will facilitate adoption of AF_XDP, make
applications using it simpler and smaller, and finally also make it
possible for applications to benefit from optimizations in the AF_XDP
user space access code. Previously, people just copied and pasted the
code from the sample application into their application, which is not
desirable.

The proposed interface is composed of two parts:

* Low-level access interface to the four rings and the packet
* High-level control plane interface for creating and setting up umems
  and AF_XDP sockets. This interface also loads a simple XDP program
  that routes all traffic on a queue up to the AF_XDP socket.

The sample program has been updated to use this new interface and in
that process it lost roughly 300 lines of code. I cannot detect any
performance degradations due to the use of this library instead of the
previous functions that were inlined in the sample application. But I
did measure this on a slower machine and not the Broadwell that we
normally use.

The rings are now called xsk_ring and when a producer operates on it, it
is xsk_ring_prod and for a consumer it is xsk_ring_cons. This way we
can get some compile time error checking that the rings are used
correctly.

Comments and contenplations:

* The current behaviour is that the library loads an XDP program (if
  requested to do so) but the clean up of this program is left to the
  application. It would be possible to implement this cleanup in the
  library, but it would require state to be kept on netdev level,
  which there is none at the moment, and the synchronization of this
  between processes. All this adding complexity. But when we get an
  XDP program per queue id, then it becomes trivial to also remove the
  XDP program when the application exits. This proposal from Jesper,
  Björn and others will also improve the performance of libbpf, since
  most of the XDP program code can be removed when that feature is
  supported.

* In a future release, I am planning on adding a higher level data
  plane interface too. This will be based around recvmsg and sendmsg
  with the use of struct iovec for batching, without the user having
  to know anything about the underlying four rings of an AF_XDP
  socket. There will be one semantic difference though from the
  standard recvmsg and that is that the kernel will fill in the iovecs
  instead of the application. But the rest should be the same as the
  libc versions so that application writers feel at home.

Patch 1: moves the pr_*() functions to a separate header file so that
         the AF_XDP code can also use them.
Patch 2: adds AF_XDP support in libbpf
Patch 3: updates the xdpsock sample application to use the libbpf functions.

Changes v2 to v3:
  * Added automatic loading of a simple XDP program that routes all
    traffic on a queue up to the AF_XDP socket. This program loading
    can be disabled.
  * Updated function names to be consistent with the libbpf naming
    convention
  * Moved all code to xsk.[ch]
  * Removed all the XDP program loading code from the sample since
    this is now done by libbpf
  * The initialization functions now return a handle as suggested by
    Alexei
  * const statements added in the API where applicable.
Changes v1 to v2:
  * Fixed cleanup of library state on error.
  * Moved API to initial version
  * Prefixed all public functions by xsk__ instead of xsk_
  * Added comment about changed default ring sizes, batch size and umem
    size in the sample application commit message
  * The library now only creates an Rx or Tx ring if the respective
    parameter is != NULL

Note that for zero-copy to work on FVL you need the following patch:
"i40e: fix potential RX buffer starvation for AF_XDP". For ixgbe,
you need a similar patch called "ixgbe: fix potential RX buffer
starvation for AF_XDP" to make ZC work with libbpf. Both have been
submitted to net.

I based this patch set on bpf-next commit 3d2af27a84a8 ("Merge branch 'bpf-flow-dissector-tests'")

Thanks: Magnus


Magnus Karlsson (3):
  libbpf: move pr_*() functions to common header file
  libbpf: add support for using AF_XDP sockets
  samples/bpf: convert xdpsock to use libbpf for AF_XDP access

 samples/bpf/Makefile              |   1 -
 samples/bpf/xdpsock.h             |  11 -
 samples/bpf/xdpsock_kern.c        |  56 ---
 samples/bpf/xdpsock_user.c        | 695 +++++++++------------------------
 tools/include/uapi/linux/if_xdp.h |  78 ++++
 tools/lib/bpf/Build               |   2 +-
 tools/lib/bpf/Makefile            |   5 +-
 tools/lib/bpf/README.rst          |  11 +-
 tools/lib/bpf/libbpf.c            |  30 +-
 tools/lib/bpf/libbpf.map          |  12 +
 tools/lib/bpf/libbpf_internal.h   |  41 ++
 tools/lib/bpf/xsk.c               | 794 ++++++++++++++++++++++++++++++++++++++
 tools/lib/bpf/xsk.h               | 132 +++++++
 13 files changed, 1260 insertions(+), 608 deletions(-)
 delete mode 100644 samples/bpf/xdpsock.h
 delete mode 100644 samples/bpf/xdpsock_kern.c
 create mode 100644 tools/include/uapi/linux/if_xdp.h
 create mode 100644 tools/lib/bpf/libbpf_internal.h
 create mode 100644 tools/lib/bpf/xsk.c
 create mode 100644 tools/lib/bpf/xsk.h

--
2.7.4

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