updated opensnoop to use bpf_perf_output

[mcaleavya]

This is really a copy of statsnoop with different functions being traced. Updated old/tools and man page. Not sure if we should merge the two scripts into one.

[4ast]

lgtm
@brendangregg pls take a look

[brendangregg]

Awesome, and works better than the old version!

Old:

# ./tools/opensnoop.py 
PID    COMM               FD ERR PATH
10976  <...>              12   0 /sys/kernel/debug/tracing/trace_pipe
[...]
10978  run                 3   0 /etc/ld.so.cache
10979  <...>               3   0 /etc/ld.so.cache
10979  <...>               3   0 /lib/x86_64-linux-gnu/libselinux.so.1
10978  run                 3   0 /lib/x86_64-linux-gnu/libtinfo.so.5
10979  <...>               3   0 /lib/x86_64-linux-gnu/libc.so.6
10979  <...>               3   0 /lib/x86_64-linux-gnu/libpcre.so.3
10979  <...>               3   0 /lib/x86_64-linux-gnu/libdl.so.2
10978  run                 3   0 /lib/x86_64-linux-gnu/libdl.so.2
10978  run                 3   0 /lib/x86_64-linux-gnu/libc.so.6
10979  <...>               3   0 /proc/filesystems

New:

# ./opensnoop.py 
PID    COMM               FD ERR PATH
2177   supervise           9   0 supervise/status.new
[...]
10990  run                 3   0 /etc/ld.so.cache
10990  run                 3   0 /lib/x86_64-linux-gnu/libnss_compat.so.2
10990  run                 3   0 /lib/x86_64-linux-gnu/libnsl.so.1
10991  run                 3   0 /lib/x86_64-linux-gnu/libnss_compat.so.2
10991  run                 3   0 /lib/x86_64-linux-gnu/libnsl.so.1
10991  run                 3   0 /etc/ld.so.cache
10991  run                 3   0 /lib/x86_64-linux-gnu/libnss_nis.so.2
10991  run                 3   0 /lib/x86_64-linux-gnu/libnss_files.so.2
10990  run                 3   0 /etc/ld.so.cache
10990  run                 3   0 /lib/x86_64-linux-gnu/libnss_nis.so.2
10990  run                 3   0 /lib/x86_64-linux-gnu/libnss_files.so.2
10990  run                 3   0 /etc/passwd
10990  run                 3   0 ./run