[RFC bpf-next 0/4] Error handling when map lookup isn't supported

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

Currently when map a lookup is failed, 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 to bpftool to do additional checking for errno when
map lookup is failed. In case of EOPNOTSUPP errno, it prints message
"lookup not supported for this map"

Prashant Bhole (4):
  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: handle EOPNOTSUPP when map lookup is failed

 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/main.h |   5 ++
 tools/bpf/bpftool/map.c  | 108 +++++++++++++++++++++++++++------------
 7 files changed, 90 insertions(+), 40 deletions(-)

-- 
2.17.1