Add new targeted error injection tool

bpf_override_return is a very powerful mechanism for error injection,
with the caveat that it requires whitelisting of the functions to be
overriden.

inject.py will take a call chain and optional set of predicates as
input, and inject the appropriate error when both the call chain and all
predicates are satisfied.

Signed-off-by: Howard McLauchlan <[email protected]>

README.md

@@ -113,6 +113,7 @@ pair of .c and .py files, and some are directories of files.
 - tools/[funcslower](tools/funcslower.py): Trace slow kernel or user function calls. [Examples](tools/funcslower_example.txt).
 - tools/[gethostlatency](tools/gethostlatency.py): Show latency for getaddrinfo/gethostbyname[2] calls. [Examples](tools/gethostlatency_example.txt).
 - tools/[hardirqs](tools/hardirqs.py): Measure hard IRQ (hard interrupt) event time. [Examples](tools/hardirqs_example.txt).
+- tools/[inject](tools/inject.py): Targeted error injection with call chain and predicates [Examples](tools/inject_example.txt).
 - tools/[killsnoop](tools/killsnoop.py): Trace signals issued by the kill() syscall. [Examples](tools/killsnoop_example.txt).
 - tools/[llcstat](tools/llcstat.py): Summarize CPU cache references and misses by process. [Examples](tools/llcstat_example.txt).
 - tools/[mdflush](tools/mdflush.py): Trace md flush events. [Examples](tools/mdflush_example.txt).

man/man8/inject.8

@@ -0,0 +1,47 @@
+.TH inject 8 "2018-03-16" "USER COMMANDS"
+.SH NAME
+inject \- injects appropriate error into function if input call chain and
+predicates are satisfied. Uses Linux eBPF/bcc.
+.SH SYNOPSIS
+.B trace -h [-I header] [-v]
+.SH DESCRIPTION
+inject injects errors into specified kernel functionality when a given call
+chain and associated predicates are satsified.
+
+This makes use of a Linux 4.16 feature (bpf_override_return())
+
+Additionally, use of the kmalloc failure mode is only possible with 
+
+ commit f7174d08a5fc ("mm: make should_failslab always available for
+ fault injection")
+
+which is in mm-tree but not yet in mainline (as of 4.16-rc5).
+
+Since this uses BPF, only the root user can use this tool.
+.SH REQUIREMENTS
+CONFIG_BPF, CONFIG_BPF_KPROBE_OVERRIDE, bcc
+.SH OPTIONS
+.TP
+\-h
+Print usage message.
+.TP
+\-v
+Display the generated BPF program, for debugging or modification.
+.TP
+\-I header
+Necessary headers to be included.
+.SH EXAMPLES
+Please see inject_example.txt
+.SH SOURCE
+This is from bcc.
+.IP
+https://github.com/iovisor/bcc
+.PP
+Also look in the bcc distribution for a companion _examples.txt file containing
+example usage, output, and commentary for this tool.
+.SH OS
+Linux
+.SH STABILITY
+Unstable - in development.
+.SH AUTHOR
+Howard McLauchlan