docs: fix commit hash and link for bpf_redirect_map()

The link wrongly pointed to the same commit as for
bpf_sk_redirect_map().

Links to recent articles on LWN.net

fix CMakefile for lua

Issue #1621 reported an issue where bcc-lua has an unresolved
symbol bcc_resolve_symname. This is a side effect of previous
cmake file refactorization which permits better control
over what features can be enabled during build time.
The refactorization caused some symbols in bcc_syms.cc
got lost in the final link which produced bcc-lua.

This patch fixed the issue by add a new static library target
bcc-lua-static and adds bcc_syms.cc to it when the library
is created and hence preserved the symbol.

Also removed unnecessary linking for clang_frontend library.
Signed-off-by: Yonghong Song <yhs@fb.com>

C++ API: Allow obtaining BPFPerfBuffer pointer for polling

Tool tcpsubnet

Fix BPFModule allocation / de-allocation mismatch

Rename kprobe_poll to perf_buffer_poll

Port fixes of biosnoop from Python to Lua

Fix bugs introduced in Lua Perf Buffer handling

docs: fix commit hash and links for bpf_set_hash() and bpf_setsockopt()

tools/cachestat: Rewrite it so it makes more sense

cachstat separation between read and writes doesn't make much sense. During tests
its seen that a workload that is supposed to be completely in the missed category
appears to be 50% hit.

This patch rewrites the BCC tool to be more inline with Brendan Gregg's original
cachestat perf tool which makes more sense:
https://github.com/brendangregg/perf-tools/blob/master/fs/cachestat
http://www.brendangregg.com/blog/2014-12-31/linux-page-cache-hit-ratio.html

Fixes Issue: #1586
Signed-off-by: Joel Fernandes <joelaf@google.com>

Helpers bpf_set_hash() and bpf_setsockopt() do not have the correct link
(bpf_set_hash()) and hash (both) in the list of BPF features per kernel
version. Fix them.

Avoid including common.h in BPFTable.h

Remove PERF_SAMPLE_CALLCHAIN logic from TRACEPOINT events

free llvm engine/context memory when rw_engine is not used

bcc utilizes MCJIT to generate final code and the code
is actually runnable in the process. This, however,
may have negative memory consumption impact.
All data will be actually allocated in memory.

For example, the following large array,
  #define TCP6_RXMIT_BUCKET_BITS 18
  struct tcp6_rxmit_tbl {
    __u64 buckets[1 << TCP6_RXMIT_BUCKET_BITS];
  };
  BPF_ARRAY(rxmit_marking_map, struct tcp6_rxmit_tbl, 1);
is added to examples/cpp/HelloWorld.cpp.
Internally, bcc will define a structure type rxmit_marking_map_table
with members `struct tcp6_rxmit_tbl leaf` and a variable
with this structure type. (see src/cc/export/helpers.h),
so that rw_engine can traverse the type to generate
proper sscanf/snprintf functions.

Even with rw_engine is disabled, the RSS still increased
from 6MB to 12MB. The array size is roughly 2MB.
The additional 4MB overhead is due to some llvm internal overhead
which I did not root cause it.

If rw_engine is disabled, we can actually free llvm
engine and context memory after copying the section data.
We do not need to copy map section data since it is not
used later on. Only map size is needed.

We cannot free llvm context memory if rw_engine is enabled since context
is shared between regular llvm module and sscanf module.

For the above HelloWorld example, if rw_engine is disabled,
this patch is able to reduce the RSS memory from 12MB to 6MB.
Signed-off-by: Yonghong Song <yhs@fb.com>

setup some bpf_module data structures correctly when rw_engine is disabled

Commit db7b8eb0 ("add a BPFModule API to disable rw_engine
sscanf/snprintf functions") permits to disable rw_engine so that
memory can be saved for structures with large arrays. As a result,
the function BPFModule::annotate(), which is used to generate
"sscanf" module, is not called when rw_engine is disabled.

Besides generating "sscanf" module, however, BPFModule::annotate()
also sets up several other data structures which are used for
map/table manipulation. This patch implements BPFModule::annotate_light(),
which will be called when rw_engine is disabled, to
setup these data structures.
Signed-off-by: Yonghong Song <yhs@fb.com>

fix hang with "trace.py --max-events #"