Improve coverage for kprobe event_re
This makes the attachment of kprobes to arbitrary events more robust.
Issue 1: Functions with '.' characters should not have similarly named
probes.
Issue 2: Functions in the blacklist should not be attached to.
Issue 3: Some functions matched by regex cannot actually be attached to,
despite not being in the blacklist...possibly the blacklist is outdated?
Instead, warn instead of error during bulk regex attach.
Issue 4: Attaching to large numbers of kprobes gets to be very slow. For
now, leave this unresolved. For reasonably sized regexes, startup times
may be acceptable, and shutdown times are actually the worse part. To
speed up shutdown, one could add the following after the last
attach_kprobe to disable auto-cleanup:
```
from bcc import open_kprobes
open_kprobes = {}
```
Then, once the program is exited, one must manually
echo "" > kprobe_events
Some numbers:
attaching to event_re='tcp_*': 2 sec startup, 15 sec shutdown
attaching to event_re='b*': 10 sec startup, 75 sec shutdown
attaching to event_re='*': unknown (>20 min) startup, unknown shutdown
The slowdowns appear to be exponential, doubtful that '*' will ever
complete.
Fixes: #199
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>