[RFC v2 bpf-next 0/5] Error handling when map lookup isn't supported

[Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>]

Currently when map a lookup fails, user space API can not make any
distinction whether given key was not found or lookup is not supported
by particular map.

In this series we modify return value of maps which do not support
lookup. Lookup on such map implementation will return -EOPNOTSUPP.
bpf() syscall with BPF_MAP_LOOKUP_ELEM command will set EOPNOTSUPP
errno. We also handle this error in bpftool to print appropriate
message.

Patch 1: adds handling of BPF_MAP_LOOKUP ELEM command of bpf syscall
such that errno will set to EOPNOTSUPP when map doesn't support lookup

Patch 2: Modifies the return value of map_lookup_elem() to EOPNOTSUPP
for maps which do not support lookup

Patch 3: Splits do_dump() in bpftool/map.c. Element printing code is
moved out into new function dump_map_elem(). This was done in order to
reduce deep indentation and accomodate further changes.

Patch 4: Changes in bpftool to print strerror() message when lookup
error is occured. This will result in appropriate message like
"Operation not supported" when map doesn't support lookup.

Patch 5: Added verifier tests to check whether verifier rejects call 
to bpf_map_lookup_elem from bpf program. For all map types those
do not support map lookup.

v2: 
- bpftool: all nit-pick fixes pointed out by Jakub
- bpftool: removed usage of error strings. Now using strerror(),
  suggested by Jakub
- added tests in verifier_tests, suggested by Alexei


Prashant Bhole (5):
  bpf: error handling when map_lookup_elem isn't supported
  bpf: return EOPNOTSUPP when map lookup isn't supported
  tools/bpf: bpftool, split the function do_dump()
  tools/bpf: bpftool, print strerror when map lookup error occurs
  selftests/bpf: verifier, check bpf_map_lookup_elem access in bpf prog

 kernel/bpf/arraymap.c                       |   2 +-
 kernel/bpf/sockmap.c                        |   2 +-
 kernel/bpf/stackmap.c                       |   2 +-
 kernel/bpf/syscall.c                        |   9 +-
 kernel/bpf/xskmap.c                         |   2 +-
 tools/bpf/bpftool/map.c                     | 102 +++++++++++------
 tools/testing/selftests/bpf/test_verifier.c | 121 +++++++++++++++++++-
 7 files changed, 199 insertions(+), 41 deletions(-)

-- 
2.17.1