In !7538, the shutdown procedure was simplified, but the ordering was
wrong, we need to shutdown the resolver, adb and requestmgr before
detaching those objects from the view, because there are cross
dependencies between at least the resolver and the adb.
Execute the shutdown(s) first, only when all three shutdowns have been
executed, detach those objects from the view.
There are leftovers from the previous refactoring effort, which left
some function declarations and comments in the header file unchanged.
Finish the renaming.
DNSRPS-enabled builds have recently been silently broken a few times due
to that feature not being tested in regular CI pipelines. Add the
--enable-dnsrps --enable-dnsrps-dl switches to the ./configure
invocation in one of the CI jobs run for all merge requests so that
DNSRPS-related build issues can be detected in advance.
It is important to note that this change by itself does NOT enable
actual testing of the DNSRPS feature as doing that requires a DNSRPS
provider library to be present on the test host.
Building the bin/tests/system/rpz/dnsrps helper binary is currently not
possible at all as the necessary compiler and linker flag definitions
are missing from bin/tests/system/Makefile.am. Add these as a basis for
addressing the problem.
Unfortunately, this is where the "mostly" bit mentioned in this commit's
subject line comes into play. The dlopen() parts of DNSRPS code have
not yet been reworked to use libuv's dlopen() API (uv_dlopen() etc.)
(See commit 37b9511ce1dd9ba66a6620c5ff617016eb81188f for prior work in
this area.) While it is certainly possible to do that, implementing
such a change without testing it in practice against a usable librpz.so
(i.e. a DNSRPS provider library) is bound to cause more trouble and
confusion than keeping the code the way it is right now. However,
making that code buildable as-is requires linking against a C standard
library that exports the dlopen(), dlsym(), and dlclose() symbols used
by the DNSRPS dynamic loading code. glibc 2.34+ satisfies that
requirement, but older glibc versions do not (these come with a separate
libdl shared library that would need to be linked in as well). (Other
C standard library implementations have not been examined.) Since the
long-term plan is to rely on libuv's dlopen() API exclusively and
detecting the shared object containing dlopen() & friends would only
pull in build system complexity for no good reason, assume for now that
the target system provides the dlopen() API in its C standard library.
This change enables the system test suite to be run for a BIND 9 build
prepared using --enable-dnsrps --enable-dnsrps-dl (on systems satisfying
the requirement explained above). However, it is important to note that
this change by itself does NOT enable actual testing of the DNSRPS
feature as doing that requires a DNSRPS provider library to be present
on the test host.
This implements node reference tracing that passes all the internal
layers from dns_db API (and friends) to increment_reference() and
decrement_reference().
It can be enabled by #defining DNS_DB_NODETRACE in <dns/trace.h> header.
The output then looks like this:
incr:node:check_address_records:rootns.c:409:0x7f67f5a55a40->references = 1
decr:node:check_address_records:rootns.c:449:0x7f67f5a55a40->references = 0
incr:nodelock:check_address_records:rootns.c:409:0x7f67f5a55a40:0x7f68304d7040->references = 1
decr:nodelock:check_address_records:rootns.c:449:0x7f67f5a55a40:0x7f68304d7040->references = 0
There's associated python script to find the missing detach located at:
https://gitlab.isc.org/isc-projects/bind9/-/snippets/1038
Change the commandline option -G to take a string that determines what
sync records should be published. It is a comma-separated string with
each element being either "cdnskey", or "cds:<algorithm>", where
<algorithm> is a valid digest type. Duplicates are suppressed.
Now that we can configure a different digest type, update the code
to honor the configuration. Update 'dns_dnssec_syncupdate' so that
the correct CDS record is published, and also when deleting CDS records,
ensure that all possible CDS records are removed from the zone.
Change one of the test cases to use a different digest type (4). The
system tests and kasp script need to be updated to take into account
the new algorithm (instead of the hard coded 2).
Commits ffa4757c792579e3bc8316df6ce4f47093e0bde3 and
77e7eac54c51c5e23bf6e0349237442ea105d02a inadvertently broke
DNSRPS-enabled builds:
- the new member of struct dns_db that holds a reference count for the
database is called 'references', not 'refcount',
- a syntax error was introduced in the designated initializer for
'rpsdb_rdataset_methods',
- rpsdb_destroy() no longer takes a 'dbp' argument.
Address all of the above issues to make DNSRPS-enabled builds work
again.
The test was setting a minimum count for recursive clients which
was not always being met (e.g. 91 instead of 100) producing a false
positive. Lower the lower bound on recursive clients for this
test to 1.
In general, it's better to do one thorough compaction when a batch of
work is complete, which is the way that `update` transactions work.
Conversely, `write` transactions are designed so that lots of little
transactions are not too inefficient, but they need explicit
compaction. This changes `dns_qp_compact()` so that it is easier to
compact any time that makes sense, if there isn't a better way to
schedule compaction. And `dns_qpmulti_commit()` only recycles garbage
when there is enough to make it worthwhile.
Add some qp-trie tracing macros which can be enabled by a
developer. These print a message when a leaf is attached or
detached, indicating which part of the qp-trie implementation
did so. The refcount methods must now return the refcount value
so it can be printed by the trace macros.
The first working multi-threaded qp-trie was stuck with an unpleasant
trade-off:
* Use `isc_rwlock`, which has acceptable write performance, but
terrible read scalability because the qp-trie made all accesses
through a single lock.
* Use `liburcu`, which has great read scalability, but terrible
write performance, because I was relying on `rcu_synchronize()`
which is rather slow. And `liburcu` is LGPL.
To get the best of both worlds, we need our own scalable read side,
which we now have with `isc_qsbr`. And we need to modify the write
side so that it is not blocked by readers.
Better write performance requires an async cleanup function like
`call_rcu()`, instead of the blocking `rcu_synchronize()`. (There
is no blocking cleanup in `isc_qsbr`, because I have concluded
that it would be an attractive nuisance.)
Until now, all my multithreading qp-trie designs have been based
around two versions, read-only and mutable. This is too few to
work with asynchronous cleanup. The bare minimum (as in epoch
based reclamation) is three, but it makes more sense to support an
arbitrary number. Doing multi-version support "properly" makes
fewer assumptions about how safe memory reclamation works, and it
makes snapshots and rollbacks simpler.
To avoid making the memory management even more complicated, I
have introduced a new kind of "packed reader node" to anchor the
root of a version of the trie. This is simpler because it re-uses
the existing chunk lifetime logic - see the discussion under
"packed reader nodes" in `qp_p.h`.
I have also made the chunk lifetime logic simpler. The idea of a
"generation" is gone; instead, chunks are either mutable or
immutable. And the QSBR phase number is used to indicate when a
chunk can be reclaimed.
Instead of the `shared_base` flag (which was basically a one-bit
reference count, with a two version limit) the base array now has a
refcount, which replaces the confusing ad-hoc lifetime logic with
something more familiar and systematic.
Adjust the dns_qp_memusage() and dns_qp_compact() functions
to be more informative and flexible about handling fragmentation.
Avoid wasting space in runt chunks.
Switch from twigs_mutable() to cells_immutable() because that is the
sense we usually want.
Drop the redundant evacuate() function and rename evacuate_twigs() to
evacuate(). Move some chunk test functions closer to their point of
use.
Clarify compact_recursive(). Some small cleanups to comments.
Use isc_time_monotonic() for qp-trie timing stats.
Use #define constants to control debug logging.
Set up DNS name label offsets in dns_qpkey_fromname() so it is easier
to use in cases where the name is not fully hydrated.
The main benchmark is `qpmulti`, which exercizes the qp-trie
transactional API with differing numbers of threads and differing data
sizes, to get some idea of how its performance scales.
The `load-names` benchmark compares the times to populate and query
and the memory used by various BIND data structures: qp-trie, hash
table (chained), hash map (closed), and red-black tree.
The `qp-dump` program is a test utility rather than a benchmark. It
populates a qp-trie and prints it out, either in an ad-hoc text
format, or as input to the graphviz `dot` program.
Ensure dns_qpkey_fromname() and dns_qpkey_toname() are inverses.
Excercise a single-threaded dns_qp_t with a fixed set of random keys
and a small chunk size. Use the table of names to ensure that the trie
is behaving as expected. This is (in effect) randomized testing like
the `qpmulti` unit test, but making use of coverage-guided fuzzing
and (in principle) test case minimization.
Randomized testing with intensive consistency and correctness checks
make it much easier to get good coverage and to shake out bugs than
hand-written unit tests for specific cases.
These tests only run in a single thread, but each test transaction
uses both a write/update and a query/snapshot, to ensure that
modifications are not visible to concurrent readers.
This change adds a number of support routines for the unit tests, and
for benchmarks and fuzz tests to be added later. It isn't necessary to
include the support routines in libdns, since they are not needed by
BIND's installed programs. So `libtest` seems like the best place for
them.
The tests themselves verify that dns_qpkey_fromname() behaves as
expected.
The error occurred when:
* The bump chunk was re-used across multiple write transactions.
In this situation the bump chunk is marked immutable, but the
immutable flag is disregarded for cells after the fender, which
were allocated in the current transaction.
* The bump chunk fills up during an insert operation, so that the
enlarged twigs vector is allocated from a new bump chunk.
* Before this happened, we should have (but didn't) made the twigs
vector mutable. This would have adjusted its refcounts as necessary.
* However, moving to a new bump chunk has a side effect: twigs that
were previously considered mutable because they are after the
fender become immutable.
* Because of this, the old twigs vector was not destroyed as expected.
* So leaves were duplicated without their refcounts being increased.
The effect is that the refcounts were lower than they should have
been, and underflowed. The tests failed to check for refcount
underflow, so this mistake was detected much later than it ideally
could have been.
After the fix, it is now correct not to ensure the twigs are mutable,
because they are about to be copied to a larger vector. Instead, we
need to find out whether `squash_twigs()` destroyed the old twigs, and
adjust the refcounts accordingly.
A qp-trie is a kind of radix tree that is particularly well-suited to
DNS servers. I invented the qp-trie in 2015, based on Dan Bernstein's
crit-bit trees and Phil Bagwell's HAMT. https://dotat.at/prog/qp/
This code incorporates some new ideas that I prototyped using
NLnet Labs NSD in 2020 (optimizations for DNS names as keys)
and 2021 (custom allocator and garbage collector).
https://dotat.at/cgi/git/nsd.git
The BIND version of my qp-trie code has a number of improvements
compared to the prototype developed for NSD.
* The main omission in the prototype was the very sketchy outline of
how locking might work. Now the locking has been implemented,
using a reader/writer lock and a mutex. However, it is designed to
benefit from liburcu if that is available.
* The prototype was designed for two-version concurrency, one
version for readers and one for the writer. The new code supports
multiversion concurrency, to provide a basis for BIND's dbversion
machinery, so that updates are not blocked by long-running zone
transfers.
* There are now two kinds of transaction that modify the trie: an
`update` aims to support many very small zones without wasting
memory; a `write` avoids unnecessary allocation to help the
performance of many small changes to the cache.
* There is also a single-threaded interface for situations where
concurrent access is not necessary.
* The API makes better use of types to make it more clear which
operations are permitted when.
* The lookup table used to convert a DNS name to a qp-trie key is
now initialized by a run-time constructor instead of a programmer
using copy-and-paste. Key conversion is more flexible, so the
qp-trie can be used with keys other than DNS names.
* There has been much refactoring and re-arranging things to improve
the terminology and order of presentation in the code, and the
internal documentation has been moved from a comment into a file
of its own.
Some of the required functionality has been stripped out, to be
brought back later after the basics are known to work.
* Garbage collector performance statistics are missing.
* Fancy searches are missing, such as longest match and
nearest match.
* Iteration is missing.
* Search for update is missing, for cases where the caller needs to
know if the value object is mutable or not.
