Make the qbipcs.h module interdependence clear (also shedding light to
some semantic dependencies) as well.
Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
It's misleading towards a random code observer, at least,
hiding the fact that what failed is actually the queing up
of some handling to perform asynchronously in the future,
rather than invoking it synchronously right away.
Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
It turns out that while 7f56f58 allowed for less blocking (thus
throughput increasing) initial handling of connections from clients
within the abstract (out-of-libqb managed) event loop, it unfortunately
subscribes itself back to such polling mechanism for UNIX-socket-check
with a default priority, which can be lower than desired (via explicit
qb_ipcs_request_rate_limit() configuration) for particular channel
(amongst attention-competing siblings in the pool, the term here
refers to associated communication, that is, both server and
on-server abstraction for particular clients). And priority-based
discrepancies are not forgiven in true priority abiding systems
(that is, unlikele with libqb's native event loop harness as detailed
in the previous commit, for which this would be soft-torelated hence
the problem would not be spotted in the first place -- but that's
expliicitly excluded from further discussion).
On top of that, it violates the natural assumption that once (single
threaded, which is imposed by libqb, at least between initial accept()
and after-said-UNIX-socket-check) server accepts the connection, it
shall rather take care of serving it (at least within stated initial
scope of client connection life cycle) rather than be rushing to accept
new ones -- which is exactly what used to happen previously once the
library user set the effectively priority in the abstract poll
above the default one.
It's conceivable, just as with the former case of attention-competing
siblings with higher priority whereby they could _infinitely_ live on
at the expense of starving the client in the initial handling phase
(authentication) despite the library user's as-high-as-siblings
intention (for using the default priority for that unconditionally
instead, which we address here), the dead lock is imminent also in
this latter accept-to-client-authentication-handling case as well
if there's an _unlimited_ fast-paced arrival queue (well, limited
by with number of allowable open descriptors within the system,
but for the Linux built-in maximum of 1M, there may be no practical
difference, at least for time-sensitive applications).
The only hope then is that such dead-locks are rather theoretical,
since a "spontaneous" constant stream of either communication on
unrelated, higher-prio sibling channels, or of new connection arrivals
can as well testify the poor design of the libqb's IPC application.
That being said, unconditional default priority in the isolated
context of initial server-side client authentication is clearly
a bug, but such application shall apply appropriate rate-limiting
measures (exactly on priority basis) to handle unexpected flux
nonetheless.
The fix makes test_ipc_dispatch_*_glib_prio_deadlock_provoke tests pass.
Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
Compared to the outer world, libqb brings rather unintuitive approach
to priorities within a native event loop (qbloop.h) -- it doesn't do
an exhaustive high-to-low priorities in a batched (clean-the-level)
manner, but rather linearly adds a possibility to pick the handling
task from the higher priority level as opposed to lower priority ones.
This has the advantage of limiting the chances of starvation and
deadlock opportunities in the incorrectly constructed SW, on the other
hand, it means that libqb is not fulfilling the architected intentions
regarding what deserves a priority truthfully, so these priorities are
worth just a hint rather than urgency-based separation.
And consequently, a discovery of these deadlocks etc. is deferred to
the (as Murphy's laws have it) least convenient moment, e.g., when
said native event loop is exchanged for other (this time priority
trully abiding, like GLib) implementation, while retaining the same
basic notion and high-level handling of priorities on libqb
side, in IPC server (service handling) context.
Hence, demonstration of such a degenerate blocking is not trivial,
and we must defer such other event loop implementation. After this
hassle, we are rewarded with a practical proof said "high-level
handling [...] in IPC server (service handling) context" contains
a bug (which we are going to subsequently fix) -- this is contrasted
with libqb's native loop implementation that works just fine even
prior that fix.
Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
This way, this core part can be easily reused where needed.
Note that "ready_signaller" similarity with run_ipc_server is not
accidental, following commit will justify it.
Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
Roles specifications are currently not applied and are rather
a preparation for the actual meaningful use to come.
Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
Using i7-6820HQ CPU yields these results:
Before: ~2:54
After: ~2:26
Speedup: ~16%
The main optimization lies in how run_function_in_new_process helper is
constructed, since now, there's an actual synchronization between the
parent and its child (that needs to be prioritized here, which is
furthermore help with making the parent immediately give up it's
processor possession) after the fork, so that a subsequent sleep is
completely omitted -- at worst (unlikely), additional sleep round(s)
will need to be undertaken as already arranged for (and now, just
400 ms is waited rather than excessive 1 second).
Another slight optimization is likewise in omission of sleep where
the control gets returned to once the waited for process has been
suceesfully examined post-mortem, without worries it's previous
life is still resounding.
Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
There's some slight reserve for when bigger PID ranges are in use.
The method to yield the limit on prefix string was derived from
practical experience (rather than based on exact calculations).
Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
It's hard to predict the length of formatted output, so we'd better
notice (and abort) if the description is truncated. Incidentally,
mkdtemp() does this for us in the shared memory branch, but do an
explicit check there as well for consistency, and get rid of the wrongly
parametrized strncat() risking a buffer overflow (CONNECTION_DESCRIPTION
is not the length of the source "/qb").
Similar truncation checks should be added to qb_ipcs_{shm,us}_connect()
where they build the request/response names, and possibly to other
places using snprintf().
Use mkdtemp makes sure that IPC files are only visible to the
owning (client) process and do not use predictable names outside
of that.
This is not meant to be the last word on the subject, it's mainly a
simple way of making the current libqb more secure. Importantly, it's
backwards compatible with an old server.
It calls rmdir on the directory created by mkdtemp way too often, but
it seems to be the only way to be sure that things get cleaned up on
the various types of server/client exit. I'm sure we can come up with
something tidier for master but I hope this, or something similar, will
be OK for 1.0.x.
Use mkdtemp makes sure that IPC files are only visible to the
owning (client) process and do not use predictable names outside
of that.
This is not meant to be the last word on the subject, it's mainly a
simple way of making the current libqb more secure. Importantly, it's
backwards compatible with an old server.
It calls rmdir on the directory created by mkdtemp way too often, but
it seems to be the only way to be sure that things get cleaned up on
the various types of server/client exit. I'm sure we can come up with
something tidier for master but I hope this, or something similar, will
be OK for 1.0.x.
build test binaries at "make" or "make all" instead of "make check".
this is necessary if it´s not possible to run make check during make rpm.
Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>
There were a few missed leftovers in d6875f2 regarding compatibility
with sed on FreeBSD (some commands do require a newline and/or
backslash separation).
Merges: #335
Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
Proper Libs.private enables linking applications statically against
libqb: static archives (.a) don't carry their own dependency
information, unlike shared libraries (.so). Modern libc versions
include socket and RT functions, so socket_LIBS and rt_LIBS will be
empty there, but we include them for strict correctness on older
platforms; basically, we're matching libqb_la_LIBADD here.
Consequently, nsl_LIBS and GLIB_LIBS don't enter this field, since they
are only used in the examples and tests, not in the library proper.
Cflags, on the other hand, is emitted all the time and (under GCC)
propagates the -pthread option (which also affects the preprocessing
stage) to all users of libqb even when compiling modules or linking
everything dynamically.
Signed-off-by: Ferenc Wágner <wferi@debian.org>
