WCFS tests follow bytestring model from the beginning because it
operates with binary data and binary messages to/from WCFS server. It
all works ok on py2, but running tests on py3 yielded several problems.
For example str and bytes were mixed in the innermost part of _assertBlk

        def _(ctx, ev):
            assert t.cached()[blk] == cached
            ev.append('read pre')

            # access data with released GIL so that the thread that reads data from
            # head/watch can receive pin message. Be careful to handle cancellation,
            # so that on error in another worker we don't get stuck and the
            # error can be propagated to wait and reported.
            #
            # we handle cancellation by spawning read in another thread and
            # waiting for either ctx cancel, or read thread to complete. This
            # way on ctx cancel (e.g. assertion failure in another worker), the
            # read thread can remain running even after _assertBlk returns, and
            # in particular till the point where the whole test is marked as
            # failed and shut down. But on test shutdown .fmmap is unmapped for
            # all opened tFiles, and so read will hit SIGSEGV. Prepare to catch
            # that SIGSEGV here.
            have_read = chan(1)
            def _():
                try:
                    b = read_exfault_nogil(blkview[0:1])
                except SegmentationFault:
                    b = 'FAULT'
                t._blkaccess(blk)
                have_read.send(b)
            go(_)
            _, _rx = select(
                ctx.done().recv,    # 0
                have_read.recv,     # 1
            )
            if _ == 0:
                raise ctx.err()
            b = _rx

    >       ev.append('read ' + b)
    E       TypeError: can only concatenate str (not "bytes") to str

bytes input was split with str delimiter

    def _loadStats(t): # -> {}
        stats = {}
        for l in t.wc._read(".wcfs/stats").splitlines():
            # key : value
>           k, v = l.split(':')
E           TypeError: a bytes-like object is required, not 'str'

and str object rejected when assigning to C `char*`:

    Traceback (most recent call last):
      File "golang/_golang.pyx", line 156, in golang._golang.__goviac
      File "wcfs/internal/wcfs_test.pyx", line 58, in wendelin.wcfs.internal.wcfs_test._tWCFS._abort_ontimeout
    TypeError: expected bytes, str found

-> Fix all those overlooks by consistently using bytestrings everywhere.

On py3 the implementation depends on nexedi/pygolang!21,
but on py2 it works both with and without pygolang bstr patches.

Preliminary history:

    vnmabus/wendelin.core@af56bd31

but it takes the reverse approach and mixes in pytest.approx for
timestamp assert which is unrelated to the topic and is not correct as
default pytest.approx behaviour is to use 1e-6 relative precision which
results in ~1700s seconds tolerance instead of intended 1µs:

    In [1]: import pytest
    In [2]: import time

    In [3]: t = time.time()

    In [4]: t
    Out[4]: 1727271692.0636573

    In [5]: t == t
    Out[5]: True

    In [6]: t == pytest.approx(t+1000)
    Out[6]: True

    In [7]: t == pytest.approx(t+2000)
    Out[7]: False

So using pytest.approx resulted in tests to become accepting faulty wcfs
behaviour.

Timestamp assert will be handled properly in the next patch.
Co-authored-by: Carlos Ramos Carreño <carlos.ramos@nexedi.com>

wcfs/client/_wcfs.pyx provides Cython wrapper over C++ WCFS client that
works with bytes-based std::string messages. On py2 everything works ok,
but on py3, due to this, it rejects str given as input argument, e.g. as follows:

    ```python
    _____________________________ test_join_autostart ______________________________

        @func
        def test_join_autostart():
            zurl = testzurl
            with raises(RuntimeError, match="wcfs: join .*: server not running"):
                wcfs.join(zurl, autostart=False)

            assert wcfs._wcregistry == {}
            def _():
                assert wcfs._wcregistry == {}
            defer(_)

    >       wc = wcfs.join(zurl, autostart=True)

    wcfs/wcfs_test.py:164:
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    wcfs/__init__.py:225: in join
        wc = WCFS(mntpt, fwcfs, wcsrv)
    ../../venvs/wendelin.core/lib/python3.9/site-packages/decorator.py:232: in fun
        return caller(func, *(extras + args), **kw)
    ../pygolang/golang/__init__.py:125: in _
        return f(*argv, **kw)
    wcfs/__init__.py:167: in __init__
        wc.mountpoint = mountpoint
    wcfs/client/_wcfs.pyx:44: in wendelin.wcfs.client._wcfs.PyWCFS.mountpoint.__set__
        def __set__(PyWCFS pywc, string v):
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    >   ???
    E   TypeError: expected bytes, str found
    ```

because by default Cython treats std::string as related to bytes on py side.

-> Fix it by accepting both str and bytes as input for all methods
   arguments related to strings.

For returned strings care to return them as strings, not bytes, to which
Cython converts std::string by default because calling code expects
returned messages to have string semantic. Though we return the data as
bytestring, not unicode, as the rest of the testsuite also assumes
binary messages reception from WCFS server.

NOTE even though it was me to originally suggest in private to use

    cython: c_string_type=str, c_string_encoding=utf8

so that str type is accepted as input, later, when having a broader
look, I realized that there are two problems with the above directives.
First the directives affect not only the input, but also any std::string
returned becomes returned as unicode instead of bytes/bytestr previously.
However as explained above the higher level expects binary semantic from
returned messages. And second if WCFS sends a message with invalid UTF-8
data, it will result in exception thrown on the client instead of
actually returning sent data to the caller. This makes debugging more
difficult and last thing I want to happen is, when WCFS sends some
garbage, to get a UnicodeDecodeError instead of actually seeing the message
and higher level assert saying that that message is unexpected with
providing details.

So do all the in- and out- conversions by hand instead with controlling
desired semantics ourselves.

On py3 the implementation depends on nexedi/pygolang!21,
but on py2 it works both with and without pygolang bstr patches.

Preliminary history:

    vnmabus/wendelin.core@47c27b03Co-authored-by: Carlos Ramos Carreño <carlos.ramos@nexedi.com>

Treegen.py was using bytes valv and iterating it to get tree keys to
be set, but on py3 iterating bytes yields integer not bytes and so with
py3 e.g. TestΔBTail was failing as

    --- FAIL: TestΔBTail (1.21s)
    panic: root['treegen/values']: key ['a']: expected str, got int64 [recovered]
            panic: file:///tmp/TestΔBTail1569960846/001/1.fs: @03fb8a9c91bba733: get blktab: root['treegen/values']: key ['a']: expected str, got int64 [recovered]

-> Fix it by reworking treegen.py to operate in strings domain and
   adjusting treeenv.go loader to use pickle.AsString correspondingly.

   On py3 the implementation depends on nexedi/pygolang!21,
   but on py2 it works both with and without pygolang bstr patches.

Preliminary history:

    vnmabus/wendelin.core@eca099bc
    vnmabus/wendelin.core@5a2b639c
    vnmabus/wendelin.core@fadc5a07

but there we were operating in mixed string/bytes mode with cluttering
the code with .encode('ascii') calls and potentially missing to handle
some logic right because on py3 str == bytes returns False, not raises,
and with mixed types it is easy to miss some logic where conversion is
needed if the outcome depends on values comparison.

Switching to work in strings domain uniformly avoids those problem in
principle and by doing only one thing locally.
Co-authored-by: Carlos Ramos Carreño <carlos.ramos@nexedi.com>

Previously TestZBlk was xfailing as e.g.

        --- FAIL: TestZBlk/py3_pickle3 (0.00s)
    panic: ZBlk0(0000000000000002): loadBlkData: wendelin.bigfile.file_zodb.ZBlk0(0000000000000002): activate: pysetstate: expect str; got ogórek.Bytes [recovered]
            panic: ZBlk0(0000000000000002): loadBlkData: wendelin.bigfile.file_zodb.ZBlk0(0000000000000002): activate: pysetstate: expect str; got ogórek.Bytes

because on py3 ZBlk data is saved as bytes while zblk.go code was trying
to decode it as bytestring (str from py2).

-> Fix that by adjusting ZBlk/go to follow py3 model with ZBlk data being
   considered to be bytes but also accepting bytestr from py2 for that.

Now on go side loading ZBlk works for all py2_pickle{1,2,3} and
py3_pickle3 data.

This brings ZODB/go updates to support Python3 from
neo!8 that we will need to
support Python3(*). For now do not add any py3 support on wcfs side - just
update neo/go with preserving wcfs/py2 in working state.

Note that this ZODB/go update brings backward incompatible changes to
activate StrictUnicode and PyDict modes(+) on unpickling and also changes
API of zodb.Map to follow that PyDict mode. We thus need to update
go bits inside wcfs because else compilation and tests, expectedly,
start to break in the following ways

    # lab.nexedi.com/nexedi/wendelin.core/wcfs/internal/xbtree/xbtreetest
    internal/xbtree/xbtreetest/treeenv.go:292:24: zroot.Data undefined (type *zodb.Map has no field or method Data)

    # lab.nexedi.com/nexedi/wendelin.core/wcfs/internal/zdata [lab.nexedi.com/nexedi/wendelin.core/wcfs/internal/zdata.test]
    ./δftail_test.go:737:16: zroot.Data undefined (type *zodb.Map has no field or method Data)

    --- FAIL: TestZBlk (0.00s)
        --- FAIL: TestZBlk/py2_pickle1 (0.00s)
    panic: ZBlk0(0000000000000002): loadBlkData: wendelin.bigfile.file_zodb.ZBlk0(0000000000000002): activate: pysetstate: expect str; got ogórek.ByteString [recovered]
            panic: ZBlk0(0000000000000002): loadBlkData: wendelin.bigfile.file_zodb.ZBlk0(0000000000000002): activate: pysetstate: expect str; got ogórek.ByteString

    --- FAIL: TestΔFtail (0.98s)
    panic: root['treegen/values']: key ["a"]: expected str, got ogórek.ByteString [recovered]
            panic: file:///tmp/TestΔFtail4275282346/001/1.fs: @03fb8a25642d1e88: get blktab: root['treegen/values']: key ["a"]: expected str, got ogórek.ByteString [recovered]
            panic: file:///tmp/TestΔFtail4275282346/001/1.fs: @03fb8a25642d1e88: get blktab: root['treegen/values']: key ["a"]: expected str, got ogórek.ByteString

    --- FAIL: TestΔBTail (1.13s)
    panic: root['treegen/values']: key ["a"]: expected str, got ogórek.ByteString [recovered]
            panic: file:///tmp/TestΔBTail3238267558/001/1.fs: @03fb8a212cd06933: get blktab: root['treegen/values']: key ["a"]: expected str, got ogórek.ByteString [recovered]
            panic: file:///tmp/TestΔBTail3238267558/001/1.fs: @03fb8a212cd06933: get blktab: root['treegen/values']: key ["a"]: expected str, got ogórek.ByteString

The changes are minimal just to keep wcfs/py2 working ok. We will do more changes in the follow-up patches to support py3.

All the changes in go.mod and go.sum are produced automatically by sole `go get lab.nexedi.com/kirr/neo/go@t+ypy3`.

(*) see neo@efde5253...6235fb60 for full list of changes.
(+) see neo@078b6262, neo@1e87fe5b,
    https://github.com/kisielk/og-rek/pull/68 and https://github.com/kisielk/og-rek/pull/75 for details.

Our "as int64" code was put into ogórek as generalized utility in
https://github.com/kisielk/og-rek/commit/010fbd2e.

Going from v1.2.0 to e691997e3596 brings in StrictUnicode + PyDict modes and other
improvements: https://github.com/kisielk/og-rek/compare/v1.2.0...e691997e3596. We will
need those improvements in the next patches.

Previously we were testing ZBlk loading on Go side only with data generated by
python2 and pickle protocol=2. However even on py2 there are more pickle
protocols that are in use, and also there is python3.

-> Modernize testdata/zblk_test_gen.py to use run_with_all_zodb_pickle_kinds
   that was recently added as part of nexedi/zodbtools@f9d36ba7
   and generate test data with both python2 and python3. It is handy to
   use py2py3-venv(*) to prepare python environment to do that.

   Adjust tests on Go side to verify how ZBlk is loaded for all generated zkinds.

py2_pickle1, py2_pickle2 and py2_pickle3 are handled well.
ZBlk test for py3_pickle3 currently fails with

        --- FAIL: TestZBlk/py3_pickle3 (0.01s)
    panic: ZBlk0(0000000000000002): loadBlkData: wendelin.bigfile.file_zodb.ZBlk0(0000000000000002): activate: pysetstate: expect str; got ogórek.Bytes [recovered]

and so is marked with "xfail".

We will fix tests for py3_pickle3 in follow-up patches.

(*) see nexedi/zodbtools@fac2f190

/reviewed-by @kirr
/reviewed-on !32

This patch updates NEO/go to include a patch that fixes
non-deterministic crashs for 'wendelin.core'. Its tradeoff is however a
moderate memory leak. This leak is going to be fixed later when a new
golang version is released. See more details about this here:
kirr/neo@ee23551d

/reviewed-by @kirr
/reviewed-on !32

sendReq has two phases: a) send request, and b) read reply. When there
is an error on the first phase, e.g. client does not read what wcfs is
trying to send, it returns an error like

    pin #2 @03fb63abd6d65b33: sendReq: send .2: context deadline exceeded

however when there is an error on the second phase, e.g. client does not
reply to wcfs request, it currently returns an error like

    pin #2 @03fb63abd6d65b33: sendReq: context deadline exceeded

which is not clear to interpret about which part was problematic.

After this patch the error for the second case becomes

    pin #2 @03fb63abd6d65b33: sendReq: waiting for reply: context deadline exceeded

which is easier to interpret.

/reviewed-by @levin.zimmermann
/reviewed-on nexedi/wendelin.core!31

This patch updates:

- github.com/golang/glog: we already wanted to do so in
    !23,
    but we deferred it to keep go 1.18 support. However in recent patches
    we already dropped go 1.18 support and we can therefore update glog now.
- lab.nexedi.com/kirr/neo/go: add fix in handshake, see here for more information:
    kirr/neo@d75f4ac2 and
    kirr/neo@03db1d8a

This patch doesn't update:

- github.com/hanwen/go-fuse: This was updated upstream and Kirill already
    reviewed and integrated patches in custom branch. However when updating
    go-fuse to v2.4.3-0.20240904154523-9546fc238dc6 (this is
    kirr/go-fuse@9546fc23),
    WCFS tests fail on my machine [1] => let's defer update
- github.com/kisielk/og-rek: there are new patches that will be needed
    in the future, but we didn't update NEO/go og-rek dependency yet,
    so let's defer the update in wendelin.core until we updated og-rek
    in NEO/go
- github.com/johncgriffin/overflow: no update on upstream
- github.com/pkg/errors: no update on upstream
- github.com/stretchr/testify: This was already updated with
    c559ec1a
    'testify' seems to have a major release in the future which may break
    some of our test code, but for now major version 1 is still the
    stable release.

----
kirr: I confirm that
kirr/go-fuse@9546fc23 brings in
regression to WCFS tests. It seems I missed some error in that go-fuse
update and it will need to be bisected and debugged.

---

[1] Test failure log:

========================================== FAILURES ==========================================
______________________________________ test_wcfs_basic _______________________________________

    @func
    def test_wcfs_basic():
        t = tDB(); zf = t.zfile
        defer(t.close)

        # >>> lookup non-BigFile -> must be rejected
        with raises(OSError) as exc:
            t.wc._stat("head/bigfile/%s" % h(t.nonzfile._p_oid))
        assert exc.value.errno == EINVAL

        # >>> file initially empty
        f = t.open(zf)
        f.assertCache([])
        f.assertData ([], mtime=t.at0)

        # >>> (@at1) commit data -> we can see it on wcfs
        at1 = t.commit(zf, {2:'c1'})

        f.assertCache([0,0,0])  # initially not cached
        f.assertData (['','','c1'], mtime=t.head)

        # >>> (@at2) commit again -> we can see both latest and snapshotted states
        # NOTE blocks e(4) and f(5) will be accessed only in the end
        at2 = t.commit(zf, {2:'c2', 3:'d2', 5:'f2'})

        # f @head
>       f.assertCache([1,1,0,0,0,0])

wcfs/wcfs_test.py:1341:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

t = <wcfs.wcfs_test.tFile instance at 0x7ff61457b960>, incorev = [1, 1, 0, 0, 0, 0]

    def assertCache(t, incorev):
>       assert t.cached() == incorev
E       assert [0, 0, 0, 0, 0, 0] == [1, 1, 0, 0, 0, 0]
E         At index 0 diff: 0 != 1
E         Use -v to get the full diff

wcfs/wcfs_test.py:791: AssertionError
------------------------------------ Captured stdout call ------------------------------------

M: commit -> @at0 (03fb5dfbe3c1cd55)

M: commit -> @at1 (03fb5dfbe4936a66)
M:      f<0000000000000002>     [2]

M: commit -> @at2 (03fb5dfbe4d01166)
M:      f<0000000000000002>     [2, 3, 5]
>>> Change history by file:

f<0000000000000002>:
                                0 1 2 3 4 5 6 7
                                a b c d e f g h
        @at0 (03fb5dfbe3c1cd55)
        @at1 (03fb5dfbe4936a66)     2
        @at2 (03fb5dfbe4d01166)     2 3   5

------------------------------------ Captured stderr call ------------------------------------
I0917 12:43:53.392222  124283 wcfs.go:2752] start "/dev/shm/wcfs/0ca22ca24e4cff2d01c10aa546fe5d5ac64bce72" "file:///tmp/testdb_fs.z5ZoMH/1.fs"
I0917 12:43:53.392282  124283 wcfs.go:2758] (built with go1.21.13)
W0917 12:43:53.392404  124283 storage.go:232] zodb: FIXME: open file:///tmp/testdb_fs.z5ZoMH/1.fs: raw cache is not ready for invalidations -> NoCache forced
W0917 12:43:53.567807  124283 wcfs.go:2331] /head/bigfile: lookup "0000000000000001": bigfopen 0000000000000001 @03fb5dfbe3c1cd55: invalid argument: ZODB.Broken("persistent.Persistent") is not a ZBigFile
I0917 12:43:53.710208  124283 wcfs.go:2933] stop "/dev/shm/wcfs/0ca22ca24e4cff2d01c10aa546fe5d5ac64bce72" "file:///tmp/testdb_fs.z5ZoMH/1.fs"
------------------------------------- Captured log call --------------------------------------
WARNING  ZODB.FileStorage:FileStorage.py:412 Ignoring index for /tmp/testdb_fs.z5ZoMH/1.fs
_________________________________ test_wcfs_watch_vs_access __________________________________

    @func
    def test_wcfs_watch_vs_access():
        t = tDB(); zf = t.zfile; at0=t.at0
        defer(t.close)

        f = t.open(zf)
        at1 = t.commit(zf, {2:'c1'})
        at2 = t.commit(zf, {2:'c2', 3:'d2', 5:'f2'})
        at3 = t.commit(zf, {0:'a3', 2:'c3', 5:'f3'})

        f.assertData(['a3','','c3','d2','x','x'])
        f.assertCache([1,1,1,1,0,0])

        # watched + commit -> read -> receive pin messages.
        # read vs pin ordering is checked by assertBlk.
        #
        # f(5) is kept not accessed to check later how wcfs.go handles δFtail
        # rebuild after it sees not yet accessed ZBlk that has change history.
        wl3  = t.openwatch();  w3 = wl3.watch(zf, at3);  assert at3 == t.head
        assert w3.at     == at3
        assert w3.pinned == {}

        wl3_ = t.openwatch();  w3_ = wl3_.watch(zf, at3)
        assert w3_.at     == at3
        assert w3_.pinned == {}

        wl2  = t.openwatch();  w2 = wl2.watch(zf, at2)
        assert w2.at     == at2
        assert w2.pinned == {0:at0, 2:at2}

        # w_assertPin asserts on state of .pinned for {w3,w3_,w2}
        def w_assertPin(pinw3, pinw3_, pinw2):
            assert w3.pinned   == pinw3
            assert w3_.pinned  == pinw3_
            assert w2.pinned   == pinw2

        f.assertCache([1,1,1,1,0,0])
        at4 = t.commit(zf, {1:'b4', 2:'c4', 5:'f4', 6:'g4'})
>       f.assertCache([1,0,0,1,0,0,0])

wcfs/wcfs_test.py:1702:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

t = <wcfs.wcfs_test.tFile instance at 0x7ff614512050>, incorev = [1, 0, 0, 1, 0, 0, ...]

    def assertCache(t, incorev):
>       assert t.cached() == incorev
E       assert [0, 0, 0, 0, 0, 0, ...] == [1, 0, 0, 1, 0, 0, ...]
E         At index 0 diff: 0 != 1
E         Use -v to get the full diff

wcfs/wcfs_test.py:791: AssertionError
------------------------------------ Captured stdout call ------------------------------------

M: commit -> @at0 (03fb5dfc0fd82300)

M: commit -> @at1 (03fb5dfc10b92ecc)
M:      f<0000000000000049>     [2]

M: commit -> @at2 (03fb5dfc10cee9dd)
M:      f<0000000000000049>     [2, 3, 5]

M: commit -> @at3 (03fb5dfc1100c999)
M:      f<0000000000000049>     [0, 2, 5]

C: setup watch f<0000000000000049> @at3 (03fb5dfc1100c999)

C: setup watch f<0000000000000049> @at3 (03fb5dfc1100c999)

C: setup watch f<0000000000000049> @at2 (03fb5dfc10cee9dd)

M: commit -> @at4 (03fb5dfc120ed611)
M:      f<0000000000000049>     [1, 2, 5, 6]
>>> Change history by file:

f<0000000000000049>:
                                0 1 2 3 4 5 6 7
                                a b c d e f g h
        @at0 (03fb5dfc0fd82300)
        @at1 (03fb5dfc10b92ecc)     2
        @at2 (03fb5dfc10cee9dd)     2 3   5
        @at3 (03fb5dfc1100c999) 0   2     5
        @at4 (03fb5dfc120ed611)   1 2     5 6

------------------------------------ Captured stderr call ------------------------------------
I0917 12:44:03.733037  125217 wcfs.go:2752] start "/dev/shm/wcfs/0ca22ca24e4cff2d01c10aa546fe5d5ac64bce72" "file:///tmp/testdb_fs.z5ZoMH/1.fs"
I0917 12:44:03.733126  125217 wcfs.go:2758] (built with go1.21.13)
W0917 12:44:03.733418  125217 storage.go:232] zodb: FIXME: open file:///tmp/testdb_fs.z5ZoMH/1.fs: raw cache is not ready for invalidations -> NoCache forced
I0917 12:44:04.475273  125217 wcfs.go:2933] stop "/dev/shm/wcfs/0ca22ca24e4cff2d01c10aa546fe5d5ac64bce72" "file:///tmp/testdb_fs.z5ZoMH/1.fs"
============================ 2 failed, 42 passed in 55.81 seconds ============================
I0917 12:44:17.882140  125540 wcfs.go:2933] stop "/dev/shm/wcfs/c4d833a0bdea4c51decf5425b8ad2cc4d017280f" "file:///tmp/testdb_fs.bvHBy9/1.fs"
make: *** [Makefile:174: test.wcfs] Error 1

/reviewed-by @kirr
/reviewed-on !30

The WCFS documentation specifies [1]:

- - - 8> - - - 8> - - -

If a client, on purpose or due to a bug or being stopped, is slow to respond
with ack to file invalidation notification, it creates a problem because the
server will become blocked waiting for pin acknowledgments, and thus all
other clients, that try to work with the same file, will get stuck.

[...]

Lacking OS primitives to change address space of another process and not
being able to work it around with ptrace in userspace, wcfs takes approach
to kill a slow client on 30 seconds timeout by default.

- - - <8 - - - <8 - - -

But before, this protection wasn't implemented yet: one
faulty client could therefore freeze the whole system. With this work
this protection is implemented now: faulty clients are killed after the
timeout or any other misbehaviour in their pin handlers.

Working on this topic also resulted in several fixes and improvements
around isolation protocol implementation on the server side.

See individual patches for details.

[1] https://lab.nexedi.com/nexedi/wendelin.core/blob/38dde766/wcfs/wcfs.go#L186-208Co-authored-by: Levin Zimmermann <levin.zimmermann@nexedi.com>

/reviewed-on !18

I would only suggest one very tiny change. In go.mod we have:

    module lab.nexedi.com/nexedi/wendelin.core/wcfs

    go 1.14

I think this needs to be updated to go 1.19 due to atomic.Int64.

And maybe we just need general go mod tidy update.

/reviewed-by @kirr
/reviewed-on !18

The WCFS documentation specifies [1]:

- - - 8> - - - 8> - - -

If a client, on purpose or due to a bug or being stopped, is slow to respond
with ack to file invalidation notification, it creates a problem because the
server will become blocked waiting for pin acknowledgments, and thus all
other clients, that try to work with the same file, will get stuck.

[...]

Lacking OS primitives to change address space of another process and not
being able to work it around with ptrace in userspace, wcfs takes approach
to kill a slow client on 30 seconds timeout by default.

- - - <8 - - - <8 - - -

But before this patch, this protection wasn't implemented yet: one
faulty client could therefore freeze the whole system. With this patch
this protection is implemented now: faulty clients are killed after the
timeout or any other misbehaviour in their pin handlers.

[1] https://lab.nexedi.com/nexedi/wendelin.core/blob/38dde766/wcfs/wcfs.go#L186-208

Preliminary history:

    levin.zimmermann/wendelin.core@24904e82
    levin.zimmermann/wendelin.core@b02dcadcCo-authored-by: Levin Zimmermann <levin.zimmermann@nexedi.com>

/discussed-on !18

If a pin misbehaves or there is IO error or anything else, we want to
stop all communication on the watchlink, cancel on in-flight pin
handlers, and (TODO) kill the client with SIGBUS.

This patch organizes WatchLink shutdown on any pin error.
This functionality is indirectly tested by test_Wcfs_watch_robust and
will be also indirectly tested by faultyprotection tests.

It would be good to have dedicated tests probably, but that is,
hopefully, TODO.

/reviewed-by @levin.zimmermann
/reviewed-on !18

Pinning is critical operation whose failure will soon lead to client
being killed with SIGBUS. WCFS correctness also depend fundamentally on
pin operation, if started, to be handled by the client.

-> rework the READ handler not to cancel pin if a READ interrupt comes
   in from the OS client.

Do this via organizing WatchLink.serveCtx and running pins under this
context instead of under READ context. Later we will adjust pins to also
cancel this context on any error.

Test is, hopefully, TODO.

/reviewed-by @levin.zimmermann
/reviewed-on nexedi/wendelin.core!18

When serve is completing and going to exit, it sends an error message to
the client without any timeout. So if the client is not reading from the
channel, wcfs will get stuck waiting for the message to be consumed.

-> Fix that by trying to send that last error only during 1 second and
   ignoring errors if any

Test is, hopefully, TODO.

/reviewed-by @levin.zimmermann
/reviewed-on nexedi/wendelin.core!18

Bring in more structure:

- final watchlink cleanup is done in its own block
- cancelling spawned handlers is done in another block
- add more comments explaining things

/reviewed-by @levin.zimmermann
/reviewed-on !18

Previously we were using .sk.CloseRead() to interrupt sk.Read(), but
that is not necessary since .sk, relying on xio.Pipe, implements
xio.Reader natively with full support for cancellation.

The original code to cancel via CloseRead comes from mid 2019 and predates

kirr/go123@7ad867a3
kirr/go123@0e368363
kirr/go123@0bdac628
kirr/go123@9db4dfac
kirr/go123@d2dc6c09

And in kirr/wendelin.core@b17aeb8c and
6f0cdaff (wcfs: Provide isolation to clients), it seems, I missed to
update WatchLink.serve code to that.

Do that now because it simplifies code flow organization a bit.

/reviewed-by @levin.zimmermann
/reviewed-on !18

So far we were testing only against faulty client that reads pin
notification ok, but does not reply to the notification. But there could
be more problems:

1) a client does not read pin notification at all
2) a client closes watchlink abruptly after reading pin notification
3) a client replies to pin notification but the reply is not "ack"

The first problem, if not handled leads to whole set of clients to
become stuck on reading the same block as the faulty client. The other
problems also indicate breakage of the isolation protocol from the client
side and that wcfs can no longer be sure that it provides good
uncorrupted data to the client.

In the first case, similarly to "no reply" situation we need to kill the
client to make progress while maintaining safety as well. In the cases 2
and 3 we cannot maintain safety if the faulty client remains in the set
of live and served clients, so it is also logical to send SIGBUS/SIGKILL
to it.

Killing a client with SIGBUS is similar to how OS kernel sends SIGBUS when
a memory-mapped file is accessed and loading file data results in EIO. It is
also similar to wendelin.core 1 where SIGBUS is raised if loading file block
results in an error.

Extend tests to cover all explained scenarios.

/reviewed-by @levin.zimmermann
/reviewed-on !18

wcfs: tests: Add test to exercies faulty client that does not reply to pin triggered by readPinWatchers

Levin writes:

    This patch extends the test scope of 'test_wcfs_pintimeout_kill'. Before
    this patch, the test only ensured that a client that does not
    respond to pin requests during the initial watch request [1] is
    killed. Now it also tests that a faulty client is killed when a block
    is invalidated. Since there are no other situations where the WCFS
    server sends pin requests to a client, the tests now cover all situations
    where a faulty client might not respond. This patch therefore aims to
    increase the security that WCFS is not blocked by a faulty client.

    [1] See !18

Preliminary history:

    levin.zimmermann/wendelin.core@9d42efffCo-authored-by: Levin Zimmermann <levin.zimmermann@nexedi.com>

/discussed-on !18

We will need to use this utilitin from several places in the next patch.

/reviewed-by @levin.zimmermann
/reviewed-on !18

Currently assertBlk uses default timeout() to wait for READ operation to
complete. That works well everywhere except that in faulty
protection tests wcfs server will first need to wait for its own
pintimeout time to kill the faulty client and only then	return read
result to all non-faulty clients.

This way corresponding test, when one client fails to handle pin
notification well triggered due to READ operations, will need to use
adjusted longer timeout for the good client when doing assertBlk.

Adjust assertBlk to allow specifying custom timeout as preparatory step
for that.

/reviewed-by @levin.zimmermann
/reviewed-on !18

And make sure that that good client can setup its watch ok even
through there simultaneously is a faulty client that should get killed.

/reviewed-by @levin.zimmermann
/reviewed-on !18

If we don't the whole testing process will become killed when wcfs
becomes taught to kill clients that do not handle pin notifications
well.

Use multiprocessing to do so and to be able to interoperate with spawned
test process by sending/receiving objects to/from it.

Preliminary history:

    levin.zimmermann/wendelin.core@aef0f0e1Co-authored-by: Levin Zimmermann <levin.zimmermann@nexedi.com>

/discussed-on !18

If wcfs kills client that did not respond to pin notification in
pintimeout time, we need to wait strictly _more_ than that time to detect
whether client was killed or not. And in practice, due to noise in
operating system load and other factors, that waiting time should be
significantly greater to detect lack of expected event. However we were
waiting for exactly 1·pintimeout time and were claiming that there was
no pinkill event right after that.

-> Wait for 2·pintimeout instead of 1·pintimeout to make pinkill detection robust.

/reviewed-by @levin.zimmermann
/reviewed-on !18

The default "pin timeout" is 30s and we are going to add many tests that
exercise pinkilling functionality soon. If every such test takes
2·pintimeout time = 60s, it will result in significant time increase
needed to run WCFS tests. Avoid that by adjusting pin timeout to
one order of magnitude smaller pintimeout=3s during faulty protection
tests.

/reviewed-by @levin.zimmermann
/reviewed-on !18

This testing helper limits whole test time to detect FUSE-related
deadlocks via aborting FUSE connection on timeout. It is working good so
far. But soon we will need pinkill-related tests, where timeout will
need to be detected independently of FUSE connection. Expose tWCFS.ctx
for tests to be able to use this context and do things limited in time.
Adjust FUSE aborting to correlate exactly with this context
cancellation.

/reviewed-by @levin.zimmermann
/reviewed-on !18

We are going to add more tests on this topic + supporting infrastructure.
It makes sense to move everything related to dedicated test file first
as a preparatory step because wcfs_test.py feels already overloaded.

Plain code movement.

/reviewed-by @levin.zimmermann
/reviewed-on !18

WCFS allows issuing simultaneous watch requests and when two watch
requests are simultaneously issued for the same file there was a race in
their handling: the code was relying on w.atMu.W to protect setupWatch
from concurrent readPinWatcher, and also, seemingly from another
setupWatch running on the same file.

But there is a bug about that: lacking atomic primitive to downgrade
RWMutex from wlock to rlock, atMu.W was first fully unlocked and then
rlocked again. The code prepare wrt readPinWatcher to start running in
that unlock->rlock time window, but it was not prepared wrt another
setupWatch starting to run on the same file in that pause time.

-> Fix that via using dedicated Watch.setupMu lock that protects
   setupWatch from setupWatch.

Test is, hopefully, TODO.

My mistake from 6f0cdaff (wcfs: Provide isolation to clients)

/reviewed-by @levin.zimmermann
/reviewed-on !18

Inside readPinWatchers:

    https://lab.nexedi.com/nexedi/wendelin.core/-/blob/wendelin.core-2.0.alpha3-26-g79e6f7b9/wcfs/wcfs.go#L1536-1591

if δFtail.BlkRevAt would return an error, then f.watchMu was not
RUnlocked back, and wg.Wait was not called at all.

-> Fix that by scheduling unlock and wg wait right after f.watchMu is
   rlocked and workgroup is created.

Test is, hopefully, TODO.

My mistake from 6f0cdaff (wcfs: Provide isolation to clients)

/reviewed-by @levin.zimmermann
/reviewed-on !18

The code was already behaving like that but there was XXX to do it. Add
test to verify it is actually done.

Opened WatchLink handle is released after RELEASE because
read in WatchLink.serve, after RELEASE, returns EOF and then the code
inside WCFS does all necessary WatchLink-related cleanup:

https://lab.nexedi.com/nexedi/wendelin.core/-/blob/wendelin.core-2.0.alpha3-26-g79e6f7b9/wcfs/wcfs.go#L1828-1872

/reviewed-by @levin.zimmermann
/reviewed-on !18

This was marked as TODO in server code and not implemented.
Without this cleanup zheadSockTab was growing indefinitely after every
open/close and leaking memory.

-> Fix it via registering RELEASE handler to FUSE and removing
corresponding zheadSockTab entry from there.

/reviewed-by @levin.zimmermann
/reviewed-on !18

Report there number of inside-WCFS instances, e.g. number of tracked
BigFiles, WatchLinks etc, and also number of counted events, for example
how many times a pin event happened.

Soon we will need this statistics to implement tests e.g. for pinkilling
and other functionalities, and it might be also useful to have in general.

/reviewed-by @levin.zimmermann
/reviewed-on !18

ZWatcher says it does not need to lock wlinkMu because it is already
holding zheadMu and setupWatch runs with zheadMu locked. That is indeed
true, but the mistake here is that it i not only setupWatch that makes
access to wlinkTab. For example WatchNode.Open registers new entries
there only under wlinkMu:

https://lab.nexedi.com/nexedi/wendelin.core/-/blob/wendelin.core-2.0.alpha3-26-g79e6f7b9/wcfs/wcfs.go#L1819-1822

-> Fix it by always using wlinkMu when accessing wlinkTab.

My mistake from 6f0cdaff (wcfs: Provide isolation to clients)

Test is, hopefully, TODO.

/reviewed-by @levin.zimmermann
/reviewed-on !18

Previously we were protecting access to zheadSockTab with zheadMu
because this table was accessed from only two places: when opening
.wcfs/zhead and in zwatcher. Soon we are going to add another place that
will access this table and still using big zheadMu seem less and less
logical.

-> Switch to using dedicated lock to protect table of .wcfs/zhead opens
   as preparatory step for that.

/reviewed-by @levin.zimmermann
/reviewed-on !18

Currently zwatcher failure leads to wcfs starting to provide stale data
instead of uptodate data. Fix that by detecting zwatcher failures and
explicitly switching the filesystem to a mode where any access to
anything returns "input/output error".

Zwatcher can fail on e.g. failure to retrieve transactions from ZODB
storage or any other failure. With this patch we make sure this does not
go unnoticed.

/reviewed-by @levin.zimmermann
/reviewed-on !18

go-fuse added functionality to handle Init.MaxPages in
https://github.com/hanwen/go-fuse/commit/265a39266958.

/reviewed-by @levin.zimmermann
/reviewed-on nexedi/wendelin.core!18

We need to drop client-specific options so that NEO URI that only differ
due to client options while actually pointing to the same NEO server
are equal after normalization.

--------
kirr: See nexedi/neoppod!18 for
the discussion on this subject.

/reviewed-by @kirr
/reviewed-on nexedi/wendelin.core!28