bpf: add sk_msg helper sk_msg_pop_data

After being able to add metadata to messages with sk_msg_push_data we have also found it useful to be able to "pop" this metadata off before sending it to applications in some cases. This series adds a new helper sk_msg_pop_data() and the associated patches to add tests and tools/lib support.

Thanks!

v2: Daniel caught that we missed adding sk_msg_pop_data to the changes
data helper so that the verifier ensures BPF programs revalidate data after using this helper. Also improve documentation adding a return description and using RST syntax per Quentin's comment. And delta calculations for DROP with pop'd data (albeit a strange set of operations for a program to be doing) had potential to be incorrect possibly confusing user space applications, so fix it.

John Fastabend (3):
bpf: helper to pop data from messages
bpf: add msg_pop_data helper to tools
bpf: test_sockmap, add options for msg_pop_data() helper usage

 include/uapi/linux/bpf.h                        |  13 +-
 net/core/filter.c                               | 169 ++++++++++++++++++++++++
 net/ipv4/tcp_bpf.c                              |  14 +-
 tools/include/uapi/linux/bpf.h                  |  13 +-
 tools/testing/selftests/bpf/bpf_helpers.h       |   2 +
 tools/testing/selftests/bpf/test_sockmap.c      | 127 +++++++++++++++++-
 tools/testing/selftests/bpf/test_sockmap_kern.h |  70 ++++++++--
 7 files changed, 386 insertions(+), 22 deletions(-)

2.7.4