Add support for generic XDP mode

Reused some of the code and command-line format from kernel XDP samples.

$ sudo ./xdp_drop_count.py -S enp1s0
Printing drops per IP protocol-number, hit CTRL+C to stop
17: 36616 pkt/s
17: 19720757 pkt/s
17: 19685768 pkt/s
17: 19643601 pkt/s
17: 19694537 pkt/s
[...]
$ sudo ./xdp_drop_count.py enp1s0
Printing drops per IP protocol-number, hit CTRL+C to stop
17: 7029 pkt/s
17: 29996706 pkt/s
17: 30048705 pkt/s
17: 30261417 pkt/s
17: 30291967 pkt/s
[...]

Throughput difference is expected since generic XDP takes more
instructions per packet than optimized XDP.

v2: switch __u32 to uint32_t in bpf_attach_xdp
Signed-off-by: Andy Gospodarek <gospo@broadcom.com>

Fix bcc_resolve_symname memory leak in C++ API

Unify Perf Event related Enums and checks

Minor fixes for example and compiler warning

Add ability for users to control symboling behavior

As the symbol type check now controled by the specified
`bcc_symbol_option` and handled in lower level, there is not need to
pass the type flag to the callback anymore.

This commit makes `ProcSyms` constructor takes a `bcc_symbol_option`,
and pass it down to underlying calls to control symboling behavior.
If `nullptr` is passed, `ProcSyms` will use default setting, which is
to use debug file, verify debug file checksum, and only load function symbols.

This commit also makes `bcc_symcache_new` take a `bcc_symbol_option`
parameter and pass it to the underlying `ProcSyms` constructor.

This commit makes `bcc_resolve_symname` to take an `bcc_symbol_option`
parameter, and pass it to underlying calls to control symboling behavior.
When `NULL` is passed, it will fallback to default which is current
behavior that uses debug file, verify debug file CRC, and check all
types of symbols.

This commit also removes the unneccesary intermediate
`bcc_find_symbol_addr`.

Added documentation for usage of the API, updated most call sites to use
default with `NULL`, and fixed some memory leaks at call sites.

`bcc_resolve_symname` should free `sym->module` on error. Also remove
unused `sym_search_t`

This commit changes `bcc_foreach_symbol` to use the new `bcc_symbol_option` to
control it only wants function symbols. Also renamed it to
bcc_foreach_function_symbol and added comments for better information.

This commit maintained current behavior of the function to prefer use
debug file and check debug file CRC. We could add option to configure
that behavior in the future if needed.

This commit adds a `bcc_symbol_option` to configure various symboling
behaviors. Currently added options for reading debug file, and what type
of symbols are wanted.

This commit also makes bcc_elf_foreach_sym take a `bcc_symbol_option`
parameter and repect the specified configurations.

Use new Kernel functionality to get first key of map

This commit adds bpf_get_first_key helper, which gets the first key of
the map. It automatically tries to use the new Kernel functionality and
falls back to old Kernel behavior. This helps us unify the logic to walk
a map across different APIs (Python, C++, etc.)

Workaround for possible race in pyroute2.ipdb

In simulation.py, add a call to initdb() to force-refresh the netlink
socket and the interface list.
Signed-off-by: Brenden Blanco <bblanco@gmail.com>

remove trailing white spaces from source code files

Trailing white spaces cause problems with git.
Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>

Enable recursive scanf support for char[] as string

Improve the internal documentation for the reader and writer generated
functions in the case that u8[]=>"" is used.

Change one `+=` to `=`.
Signed-off-by: Brenden Blanco <bblanco@gmail.com>

When a bpf table contains i8[] in one of its keys/leaves, use "" to
enclose the value, rather than [ %i %i %i ... ] format. This simplifies
the code that is generated for cases such as #1154, and brings it back
under ~200ms code generation, instead of >30s. This change of format is
not particularly robust (it doesn't handle escaping the doublequote
character itself), but it should make more sense for the common case,
such as tracing files and pathnames.

The test case included tests both the functionality of the format string
handling as well as the compile time, since test_clang already has an
implicit 10second timeout limit.

Fixes: #1154
Signed-off-by: Brenden Blanco <bblanco@gmail.com>

Fix bug when finding symbols for shared libraries

llvm5.0: use input kind helper to avoid breakage

Move FileDesc to separated header file and install

Upstream llvm renamed an enum, so use a helper function that is
available in all versions to fix compatibility.
Signed-off-by: Brenden Blanco <bblanco@gmail.com>

Use late-binding to finalize snprintf/sscanf

Signed-off-by: Brenden Blanco <bblanco@gmail.com>

Fedora compile

The api should return 0, not the number of bytes successfully written
(which is what snprintf directly returns).
Signed-off-by: Brenden Blanco <bblanco@gmail.com>

Not all users require the snprintf/sscanf helpers, and in some types the
finalization can take a long time. Defer the finalization until the
first use. Wrap the invocation with a bound function such that the
BPFTable and other users don't need to keep an explicit BPFModule
reference. Use-after-free will be avoided by resetting the function to
an error-returning stub when/if the BPFModule is freed.
Signed-off-by: Brenden Blanco <bblanco@gmail.com>