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NAME | C SYNOPSIS | DESCRIPTION | RUN-TIME CONTROL | EXAMPLES | DIAGNOSTICS | ENVIRONMENT | SEE ALSO | COLOPHON |
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PMFAULT(3) Library Functions Manual PMFAULT(3)
__pmFaultInject, __pmFaultSummary, PM_FAULT_POINT,
PM_FAULT_RETURN, PM_FAULT_CHECK, PM_FAULT_CLEAR - Fault Injection
Infrastructure for QA
#include <pcp/pmapi.h>
#include <pcp/fault.h>
void __pmFaultInject(const char *ident, int class);
void __pmFaultSummary(FILE *f);
PM_FAULT_POINT(ident, class);
PM_FAULT_RETURN(retvalue);
PM_FAULT_CHECK;
PM_FAULT_CLEAR;
cc -DPM_FAULT_INJECTION=1 ... -lpcp_fault
As part of the coverage-driven changes to QA in PCP 3.6, it
became apparent that we needed someway to exercise the
``uncommon'' code paths associated with error detection and
recovery.
The facilities described below provide a basic fault injection
infrastructure (for libpcp only at this stage, although the
mechanism is far more general and could easily be extended).
A special build is required to create libpcp_fault and the
associated <pcp/fault.h> header file. Once this has been done,
new QA applications may be built with -DPM_FAULT_INJECTION=1
and/or existing applications can be exercised in presence of
fault injection by forcing libpcp_fault to be used in preference
to libpcp as described below.
In the code to be tested, __pmFaultInject defines a fault point
at which a fault of type class may be injected. ident is a
string to uniquely identify the fault point across all of the PCP
source code, so something like "libpcp/" __FILE__ ":<number>"
works just fine. The ident string also determines if a fault
will be injected at run-time or not - refer to the RUN-TIME
CONTROL section below. class selects a failure type, using one
of the following defined values (this list may well grow over
time):
PM_FAULT_ALLOC
Will cause the next call to malloc(3), realloc(3) or
strdup(3) to fail, returning NULL and setting errno to
ENOMEM. We could extend the coverage to all of the
malloc-related routines, but these three are sufficient to
cover the vast majority of the uses within libpcp.
PM_FAULT_CALL
Will cause the next call to an instrumented routine to
fail by returning an error code (possibly the new
PM_ERR_FAULT code). The actual error code is defined in
the PM_FAULT_RETURN macro at the head of an instrumented
routine. Initially, only __pmRegisterAnon(3) (returns
PM_ERR_FAULT), __pmGetPDU(3) (returns PM_ERR_TIMEOUT) and
__pmAllocResult(3) (returns NULL) were instrumented as a
proof of concept for this part of the facility, however
other routines may have this fault injection capability
added over time.
PM_FAULT_MISC
The ``other'' class, currently used with PM_FAULT_CHECK as
described below.
To allow fault injection to co-exist within the production source
code, PM_FAULT_POINT is a macro that emits no code by default,
but when PM_FAULT_INJECTION is defined this becomes a call to
__pmFaultInject. Throughout libpcp we use PM_FAULT_POINT and not
__pmFaultInject so that both libpcp and libpcp_fault can be built
from the same source code.
Similarly, the macro PM_FAULT_RETURN emits no code unless
PM_FAULT_INJECTION is defined, in which case if a fault of type
PM_FAULT_CALL has been armed with __pmFaultInject then, the
enclosing routine return with the function value retvalue.
The PM_FAULT_CHECK macro returns a value that may be 0 or 1. If
PM_FAULT_INJECTION is defined then if a fault of type
PM_FAULT_MISC has been armed with __pmFaultInject then the value
is 1 else it is 0.
PM_FAULT_CHECK is most often used in concert with the
PM_FAULT_POINT macro with the PM_FAULT_MISC class to potentially
arm a trigger, then test PM_FAULT_CHECK and if this has the value
1, then the PM_FAULT_CLEAR macro is used to clear any armed
faults, and the fault injection code is executed.
This is illustrated in the example below from
src/libpcp/src/exec.c:
pid = fork();
/* begin fault-injection block */
PM_FAULT_POINT("libpcp/" __FILE__ ":4", PM_FAULT_MISC);
if (PM_FAULT_CHECK) {
PM_FAULT_CLEAR;
if (pid > (pid_t)0)
kill(pid, SIGKILL);
setoserror(EAGAIN);
pid = -1;
}
/* end fault-injection block */
A summary of fault points seen and faults injected is produced on
stdio stream f by __pmFaultSummary.
Additional tracing (via -Dfault or pmDebugOptions.fault) and a
new PMAPI error code (PM_ERR_FAULT) are also defined, although
these will only ever be seen or used in libpcp_fault. If
pmDebugOptions.fault is set the first time __pmFaultInject is
called, then __pmFaultSummary will be called automatically to
report on stderr when the application exits (via atexit(3)).
Fault injection cannot be nested. Each call to __pmFaultInject
clears any previous fault injection that has been armed, but not
yet executed.
The fault injection infrastructure is not thread-safe and should
only be used with applications that are known to be single-
threaded.
By default, no fault injection is enabled at run-time, even when
__pmFaultInject is called.
Faults are selectively enabled using a control file, identified
by the environment variable $PM_FAULT_CONTROL; if this is not
set, no faults are enabled.
The control file (if it exists) is read the first time
__pmFaultInject is called, and contains lines of the form:
ident op number
that define fault injection guards.
ident is a fault point string (as defined by a call to
__pmFaultInject, or more usually the PM_FAULT_POINT macro). So
one needs access to the libpcp source code to determine the
available ident strings and their semantics.
op is one of the C-style operators >=, >, ==, <, <=, != or % and
number is an unsigned integer. op number is optional and the
default is >0
The semantics of the fault injection guards are that each time
__pmFaultInject is called for a particular ident, a trip count is
incremented (the first trip is 1); if the C-style expression
tripcount op number has the value 1 (so true for most ops, or the
remainder equals 1 for the % op), then a fault of the class
defined for the fault point associated with ident will be armed,
and executed as soon as possible.
Within the control file, blank lines are ignored and lines
beginning with # are treated as comments.
For an existing application linked with libpcp fault injection
may still be used by forcing libpcp_fault to be used in the place
of libpcp. The following example shows how this might be done.
$ export PM_FAULT_CONTROL=/tmp/control
$ cat $PM_FAULT_CONTROL
# ok for 2 trips, then inject errors
libpcp/events.c:1 >2
$ export LD_PRELOAD=/usr/lib/libpcp_fault.so
$ pmevent -Dfault -s 3 sample.event.records
host: localhost
samples: 3
interval: 1.00 sec
sample.event.records[fungus]: 0 event records
__pmFaultInject(libpcp/events.c:1) ntrip=1 SKIP
sample.event.records[bogus]: 2 event records
10:46:12.413 --- event record [0] flags 0x1 (point) ---
sample.event.param_string "fetch #0"
10:46:12.413 --- event record [1] flags 0x1 (point) ---
sample.event.param_string "bingo!"
__pmFaultInject(libpcp/events.c:1) ntrip=2 SKIP
sample.event.records[fungus]: 1 event records
10:46:03.416 --- event record [0] flags 0x1 (point) ---
__pmFaultInject(libpcp/events.c:1) ntrip=3 INJECT
sample.event.records[bogus]: pmUnpackEventRecords: Cannot allocate memory
__pmFaultInject(libpcp/events.c:1) ntrip=4 INJECT
sample.event.records[fungus]: pmUnpackEventRecords: Cannot allocate memory
__pmFaultInject(libpcp/events.c:1) ntrip=5 INJECT
sample.event.records[bogus]: pmUnpackEventRecords: Cannot allocate memory
=== Fault Injection Summary Report ===
libpcp/events.c:1: guard trip>2, 5 trips, 3 faults
Refer to the PCP and PCP QA source code.
The macro definitions are in src/include/pcp/fault.h.
src/libpcp/src/fault.c contains all of the the underlying
implementation.
src/libpcp_fault and src/libpcp_fault/src contains the recipe and
Makefiles for creating and installing libpcp_fault.so and
<pcp/fault.h>.
PM_FAULT_RETURN was initiallly used in the following libpcp
source files: derive_parser.y.in, pdu.c and result.c.
PM_FAULT_POINT. was initiallly used in the following libpcp
source files: derive_parser.y.in, desc.c, e_indom.c, e_labels.c,
err.c, events.c, exec.c, fetch.c, help.c, instance.c, interp.c,
labels.c, logmeta.c, pmns.c, p_profile.c and store.c.
The ``fault'' group of QA tests show examples of control file
use. To see which tests are involved
$ cd qa
$ check -n -g fault
Some non-recoverable errors are reported on stderr.
PM_FAULT_CONTROL
Full path to the fault injection control file.
LD_PRELOAD
Force libpcp_fault to be used in preference to libpcp.
PMAPI(3)
This page is part of the PCP (Performance Co-Pilot) project.
Information about the project can be found at
⟨http://www.pcp.io/⟩. If you have a bug report for this manual
page, send it to [email protected]. This page was obtained from the
project's upstream Git repository
⟨https://github.com/performancecopilot/pcp.git⟩ on 2024-06-14.
(At that time, the date of the most recent commit that was found
in the repository was 2024-06-14.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
Performance Co-Pilot PMFAULT(3)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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