* t2:
  .
  wendelin.core v2.0.alpha1

* master:
  wendelin.core v2.0.alpha1

* t2:
  *: Cosmetics
  .
  .
  lib/zodb: Mark test_zconn_at as xfail on plain ZODB4
  .
  .
  wcfs: Server.stop: Make sure to remove mount entry even if we had to use FUSE abort
  tests: Don't leak WCFS log files
  tests: Remove test NEO database after test run is over
  nxdtest: Don't run test.go for multiple GOMAXPROCS
  wcfs: Make sure to remove mountpoint directory on Server.stop
  nxdtest: Run WCFS-related tests in verbose mode on testnodes
  setup: Fix egg_info after addition of δbtail.go

* master:
  *: Cosmetics

* master:
  lib/zodb: Mark test_zconn_at as xfail on plain ZODB4

This way on plain ZODB4 the following non-wcfs tests will continue to
pass

   test.py/fs-!wcfs
   test.py/zeo-!wcfs
   test.py/neo-!wcfs

instead of failing as e.g. in here:

   https://nexedijs.erp5.net/#/test_result_module/20211116-123A66706

On plain ZODB4 WCFS-related functionality - which uses zconn_at - will
continue to raise corresponding assertion in WCFS-related tests, as e.g. in

https://nexedijs.erp5.net/#/test_result_module/20211116-123A66706/6

* master:
  wcfs: Server.stop: Make sure to remove mount entry even if we had to use FUSE abort
  tests: Don't leak WCFS log files
  tests: Remove test NEO database after test run is over
  nxdtest: Don't run test.go for multiple GOMAXPROCS
  wcfs: Make sure to remove mountpoint directory on Server.stop
  nxdtest: Run WCFS-related tests in verbose mode on testnodes
  setup: Fix egg_info after addition of δbtail.go

* t2:
  .
  fixup! wcfs: Handle ZODB invalidations
  .
  .
  wcfs/internal/mm: Complete the package
  fixup! wcfs: client: Provide client package to care about isolation protocol details
  lib/zodb: zconn_at: Fix how ZODB4 is asserted to be patched
  .
  .
  .
  .
  .

Server.stop currently tries to unmount, and if that fails invokes FUSE
abort and kills wcfs.go . However it does not call unmount the second
time after such abort, and this way the filesystem remains mounted (in
ENOTCONN state) and rmdir(mountpoint) fails.

-> Fix it by calling unmount the second time if we had to abort FUSE
connection. In that second try use lazy unmounting, because regular
unmount can still fail with "Device or resource busy" since there
could be still client file descriptors left pointing to the mounted
filesystem. With lazy mode unmounting + followup rmdir, hopefully,
always succeeds.

Here is example test run where one test timed out, FUSE connection was
aborted, but neither the filesystem was unmounted, nor mountpoint
directory was deleted, which led to all followup tests failing in setup
assert that testmountpoint does not exist:

https://nexedijs.erp5.net/#/test_result_module/20211112-1ACEA62D/22

This patch should fix those followup failures + fix another leakage of
WCFS mounts in real services.

By default every WCFS run creates several files in /tmp/wcfs.*.log.* and
without explicit cleanup those files are left hanging on testnodes. Over
last ~6 months we accumulated ~ 300K such files.

Don't allow those files to be leaked by instructing WCFS to log to
stderr during test run. This should be also useful to see details in the
test output.

With NEO we were creating test database on /tmp but we were not deleting
it in the end. As the result many /tmp/neo_XXXXXX non-empty directories
were being leaked.

-> Fix it by creating testdb directory outselves and removing it at the
end, similarly to FileStorage and ZEO.

Fixes: 7fc4ec66 (tests: Allow to test with ZEO & NEO ZODB storages)

We run tests with different GOMAXPROCS because some WCFS bugs are only
likely to trigger when there is only 1 or 2 main OS thread(s) in WCFS.

However test.go does not exercise filesystem functionality - it runs
unit tests for ZBlk decoding, ΔBtail and similar. At the same time
test.go:* currently occupies ~ 50% of whole time to run full testsuite
with the main consumer being ΔBtail random testing.

-> Run test.go only once. This should save ~ 1000s for each run and
lower whole time to run wendelin.core testsuite on testnode from
~60m -> to ~40 minutes.

Else every time test.py/wcfs is run several empty directories are left
in /dev/shm/wcfs - each corresponding to WCFS server that was
automatically spawned and stopped at the end of the test. Over time this
can accumulate to some big number as e.g. ~20000 of such directories
were left on the testnode during last 6 months.

This are the early days of WCFS - we want full details which in default
configuration might not be available to see if WCFS gets stuck for one
reason or another. See added comments for details.

`python setup.py egg_info` stopped working after we added non-ASCII
files, e.g. δbtail.go in 2ab4be93 (wcfs: xbtree: ΔBtail) and δftail.go
in f980471f (wcfs: zdata: ΔFtail):

    (neo) (z-dev) (g.env) kirr@deca:~/src/neo/src/lab.nexedi.com/nexedi/wendelin.core$ python setup.py egg_info
    running egg_info
    writing requirements to wendelin.core.egg-info/requires.txt
    writing wendelin.core.egg-info/PKG-INFO
    writing top-level names to wendelin.core.egg-info/top_level.txt
    writing dependency_links to wendelin.core.egg-info/dependency_links.txt
    writing entry points to wendelin.core.egg-info/entry_points.txt
    package init file '__init__.py' not found (or not a regular file)
    /usr/lib/python2.7/distutils/filelist.py:64: UnicodeWarning: Unicode equal comparison failed to convert both arguments to Unicode - interpreting them as being unequal
      sortable_files.sort()
    Traceback (most recent call last):
      File "setup.py", line 416, in <module>
        """.splitlines()]
      File "/home/kirr/src/tools/go/pygolang/golang/pyx/build.py", line 118, in setup
        setuptools_dso.setup(**kw)
      File "/home/kirr/src/wendelin/venv/z-dev/lib/python2.7/site-packages/setuptools_dso/__init__.py", line 37, in setup
        _setup(**kws)
      File "/home/kirr/src/wendelin/venv/z-dev/lib/python2.7/site-packages/setuptools/__init__.py", line 162, in setup
        return distutils.core.setup(**attrs)
      File "/usr/lib/python2.7/distutils/core.py", line 151, in setup
        dist.run_commands()
      File "/usr/lib/python2.7/distutils/dist.py", line 953, in run_commands
        self.run_command(cmd)
      File "/usr/lib/python2.7/distutils/dist.py", line 972, in run_command
        cmd_obj.run()
      File "/home/kirr/src/wendelin/venv/z-dev/lib/python2.7/site-packages/setuptools/command/egg_info.py", line 296, in run
        self.find_sources()
      File "/home/kirr/src/wendelin/venv/z-dev/lib/python2.7/site-packages/setuptools/command/egg_info.py", line 303, in find_sources
        mm.run()
      File "/home/kirr/src/wendelin/venv/z-dev/lib/python2.7/site-packages/setuptools/command/egg_info.py", line 538, in run
        self.filelist.sort()
      File "/usr/lib/python2.7/distutils/filelist.py", line 64, in sort
        sortable_files.sort()
    UnicodeDecodeError: 'ascii' codec can't decode byte 0xce in position 0: ordinal not in range(128)

This happens becuase by default setuptools collects filenames as str, not
unicode, and our git_lsfiles - also registered into setuptools.file_finders
entrypoint - collects filenames as unicode. Previously everything was working
because there was no on-ASCII filenames, and so unicode vs str coercion worked
automatically. But now, after there is filename like 'δbtail.go', it stopped to
work and raises UnicodeDecodeError.

-> Fix it by adjusting git_lsfiles to collect filenames as UTF-8 encoded
strings instead of unicode.

* master: (40 commits)
  fixup! wcfs: Handle ZODB invalidations
  wcfs/internal/mm: Complete the package
  fixup! wcfs: client: Provide client package to care about isolation protocol details
  lib/zodb: zconn_at: Fix how ZODB4 is asserted to be patched
  lib/zodb: zstor_2zurl: Explicitly reject MappingStorage
  bigfile/zodb: Teach ZBigFile backend to use WCFS
  wcfs: client: Provide virtmem integration
  wcfs: client: Add wczsync package to maintain WCFS connection in sync to ZODB connection
  lib/zodb: Teach zconn_at to work on ZODB4
  lib/zodb: Add ZODB.Connection.onShutdownCallback
  lib/zodb: Teach Connection.onResyncCallback to work on ZODB4
  bigfile/py: Allow PyBigFile backend to expose "mmap overlay" functionality
  bigfile/virtmem: Introduce "mmap overlay" mode
  wcfs: client: Provide client package to care about isolation protocol details
  wcfs: Provide isolation to clients
  wcfs: Handle ZODB invalidations
  wcfs: Add FileSock FUSE utility
  wcfs: zdata: ΔFtail
  wcfs: xbtree: ΔBtail
  wcfs: xbtree: BTree-diff algorithm
  ...

Fix last-minute error that crept in during
4af54da9 :

    (neo) (z-dev) (g.env) kirr@deca:~/src/neo/src/lab.nexedi.com/nexedi/wendelin.core/wcfs$ go test
    # lab.nexedi.com/nexedi/wendelin.core/wcfs
    ./wcfs.go:957:4: Errorf format %s has arg sk of wrong type *lab.nexedi.com/nexedi/wendelin.core/wcfs.FileSock

Amends 4430de41.

Add two functions, that were developed during wendelin.core 2 α, to the
package for completeness:

- map_zero_into_ro complements map_zero_ro, but mmaps into user-provided buffer.
- sync calls msync on the provided memory.

Remove outdated TODO because test_wcfs_watch_before_create passes this
days. It was fixed after ΔFtail was taught about epochs and the fix was
reflected in 63ae8326.

Amends 10f7153a.

Fix how unpatched ZODB4 is reported to lack required patch:

Before:

    Traceback (most recent call last):
      File "/home/kirr/src/wendelin/wendelin.core/lib/tests/test_zodb.py", line 251, in test_zconn_at
        assert zconn_at(conn1) == at0
      File "/home/kirr/src/wendelin/wendelin.core/lib/zodb.py", line 162, in zconn_at
        assert 'conn:MVCC-via-loadBefore-only' in ZODB.nxd_patches, \
    AttributeError: 'module' object has no attribute 'nxd_patches'

After:

    Traceback (most recent call last):
      File "/home/kirr/src/wendelin/wendelin.core/lib/tests/test_zodb.py", line 251, in test_zconn_at
        assert zconn_at(conn1) == at0
      File "/home/kirr/src/wendelin/wendelin.core/lib/zodb.py", line 163, in zconn_at
        "nexedi/ZODB!1")
      File "/home/kirr/src/wendelin/wendelin.core/lib/zodb.py", line 191, in _zassertHasNXDPatch
        (zmajor, patch, details_link))
    AssertionError: ZODB4 is not patched with required Nexedi patch 'conn:MVCC-via-loadBefore-only'
            See nexedi/ZODB!1 for details

Fixes 1f866c00 (lib/zodb: Teach zconn_at to work on ZODB4).

* master: (36 commits)
  lib/zodb: zstor_2zurl: Explicitly reject MappingStorage
  bigfile/zodb: Teach ZBigFile backend to use WCFS
  wcfs: client: Provide virtmem integration
  wcfs: client: Add wczsync package to maintain WCFS connection in sync to ZODB connection
  lib/zodb: Teach zconn_at to work on ZODB4
  lib/zodb: Add ZODB.Connection.onShutdownCallback
  lib/zodb: Teach Connection.onResyncCallback to work on ZODB4
  bigfile/py: Allow PyBigFile backend to expose "mmap overlay" functionality
  bigfile/virtmem: Introduce "mmap overlay" mode
  wcfs: client: Provide client package to care about isolation protocol details
  wcfs: Provide isolation to clients
  wcfs: Handle ZODB invalidations
  wcfs: Add FileSock FUSE utility
  wcfs: zdata: ΔFtail
  wcfs: xbtree: ΔBtail
  wcfs: xbtree: BTree-diff algorithm
  wcfs: xbtree: blib += PPTreeSubSet, ΔPPTreeSubSet
  wcfs: xbtree: blib += RangedMap, RangedKeySet
  wcfs: tests: Tree-based testing environment
  wcfs: Set package
  ...

It is not possible for WCFS to access data of in-RAM storage of another
process. But without explicit explanation the error message is confusing
- it was something like:

    NotImplementedError: don't know how to extract zurl from <ZODB.MappingStorage.MappingStorage object at 0x7f28f04cea10>

which suggests it was just not implemented.

By using WCFS as mmap-overlay for base data(*). WCFS-mode is still opt-in
with default remaining to use old full user-space virtual memory manager
mode as initially introduced in 2015.

Wendelin.core should be draftly usable in WCFS mode now.

This patch is organized as follows:

- file_zodb.cpp provides mmap-overlay operations for WCFS implemented via
  WCFS client library.
- file_zodb.py is adjusted accordingly to use WCFS if requested.
  Low-level things specific to gluing to file_zodb.cpp are moved to _file_zodb.pyx.
- the rest of the changes are drive-by by main ones.

(*) see the following patches for what is mmap-overlay:

- fae045cc  (bigfile/virtmem: Introduce "mmap overlay" mode)
- 23362204  (bigfile/py: Allow PyBigFile backend to expose "mmap overlay" functionality)

Some preliminary history:

kirr/wendelin.core@01916f09    X Draft demo that reading data through wcfs works
kirr/wendelin.core@fd58082a    X Fix build on old GCC
kirr/wendelin.core@f622e751    X tests: Stop wcfs spawned during tests
kirr/wendelin.core@f118617b    X tests: Don't try to stop wcfs that is already exited

Provide integration with virtmem, so that WCFS Mapping can be associated
and managed under virtmem VMA. In other words provide support so that WCFS can
be used as ZBigFile backend in "mmap overlay" mode (see fae045cc "bigfile/virtmem:
Introduce "mmap overlay" mode" for description of mmap-overlay mode).

We'll need this functionality for ZBigFile + WCFS client integration.

Virtmem integration will be tested via running whole wendelin.core functional
testsuite in wcfs-mode after the next patch.

Quoting added description:

---- 8< ----

Integration with wendelin.core virtmem layer
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This client package can be used standalone, but additionally provides
integration with wendelin.core userspace virtual memory manager: when a
Mapping is created, it can be associated as serving base layer for a
particular virtmem VMA via FileH.mmap(vma=...). In that case, since virtmem
itself adds another layer of dirty pages over read-only base provided by
Mapping(+)

                 ┌──┐                      ┌──┐
                 │RW│                      │RW│    ← virtmem VMA dirty pages
                 └──┘                      └──┘
                           +
                                                   VMA base = X@at view provided by Mapping:

                                          ___        /@revA/bigfile/X
        __                                           /@revB/bigfile/X
               _                                     /@revC/bigfile/X
                           +                         ...
     ───  ───── ──────────────────────────   ─────   /head/bigfile/X

the Mapping will interact with virtmem layer to coordinate
updates to mapping virtual memory.

How it works
~~~~~~~~~~~~

Wcfs client integrates with virtmem layer to support virtmem handle
dirtying pages of read-only base-layer that wcfs client provides via
isolated Mapping. For wcfs-backed bigfiles every virtmem VMA is interlinked
with Mapping:

      VMA     -> BigFileH -> ZBigFile -----> Z
       ↑↓                                    O
     Mapping  -> FileH    -> wcfs server --> DB

When a page is write-accessed, virtmem mmaps in a page of RAM in place of
accessed virtual memory, copies base-layer content provided by Mapping into
there, and marks that page as read-write.

Upon receiving pin message, the pinner consults virtmem, whether
corresponding page was already dirtied in virtmem's BigFileH (call to
__fileh_page_isdirty), and if it was, the pinner does not remmap Mapping
part to wcfs/@revX/f and just leaves dirty page in its place, remembering
pin information in fileh._pinned.

Once dirty pages are no longer needed (either after discard/abort or
writeout/commit), virtmem asks wcfs client to remmap corresponding regions
of Mapping in its place again via calls to Mapping.remmap_blk for previously
dirtied blocks.

The scheme outlined above does not need to split Mapping upon dirtying an
inner page.

See bigfile_ops interface (wendelin/bigfile/file.h) that explains base-layer
and overlaying from virtmem point of view. For wcfs this interface is
provided by small wcfs client wrapper in bigfile/file_zodb.cpp.

(+) see bigfile_ops interface (wendelin/bigfile/file.h) that gives virtmem
    point of view on layering.

----------------------------------------

Some preliminary history:

kirr/wendelin.core@f330bd2f    X wcfs/client: Overview += interaction with virtmem layer

For ZBigFile + WCFS client integration we'll need to open WCFS
connections that observer database at the same state as current ZODB
connection. Later that WCFS connection needs to adjust its on-WCFS view
in accordance to how ZODB connection adjusts its one.

Wczsync provides a function to do so: pywconnOf(zconn) will open WCFS
connection and maintain it in sync with ZODB connection zconn.

Some preliminary history:

8bf8f23b    X bigfile/_file_zodb: Fix logic around ZSync usage
571cb737    fixup! X bigfile/_file_zodb: Fix logic around ZSync usage
a9a82d5a    X bigfile/_file_zodb: Fix ZSync to close not only wconn, but also wconn.wc through which wconn was created
cf92937f    X wcfs: Move wconn<->zconn sync functionality into wcfs.client._wczsync
7203d7ab    X wcfs: Fix ZSync to close wconn on zdb.close, even if zconn stays alive

In 3bd82127 (lib/zodb: Add zconn_at draft (ZODB5 only)) we added
zconn_at function to find out as of which state a ZODB connection is
viewing the database. That was ZODB5-only however.

Let's add support for ZODB4 now - by requiring ZODB4-wc2 - a version of
ZODB4 with MVCC backported from ZODB5: nexedi/ZODB!1

This makes wendelin.core to work on either ZODB5 or ZODB4-wc2, but not
plain ZODB4. However as zconn_at will be used only for WCFS-integration,
non-wcfs mode will continue to work on all ZODB5, ZODB4-wc2 and plain
ZODB4.

ZBigFile + WCFS client integration will use zconn_at to open WCFS
connection that corresponds to ZODB connection.

Preliminary history:

kirr/wendelin.core@1c3b7750    X zconn_at for ZODB4

Add patch to ZODB.Connection to support callback on after database is
closed. ZBigFile + WCFS client integration will use this callback to
close WCFS connection when corresponding ZODB.DB is closed.

Preliminary history:

a26d9659    X lib/zodb: Connection += onShutdownCallback

In 959ae2d0 (lib/zodb: Add patch to ZODB.Connection to support callback
on connection DB view change) we added patch for ZODB.Connection to
support callback when database view of the connection changes. At that
time the patch was working for ZODB5 and ZODB4 was TODO.
Let's add support for ZODB4 (both ZODB4 and ZODB4-wc2) now.

As a reminder: ZBigFile + WCFS client integration will use this callback
to keep WCFS connection in sync with ZODB connection.

Preliminary history:

533a4cfa     X onResyncCallback for ZODB4

This patch logically continues previous change `bigfile/virtmem:
Introduce "mmap overlay" mode` and exposes mmap-overlay functionality to
Python: if PyBigFile backend provides .blkmmapper PyCapsule the
mmap-related methods will be extracted from it and passed on through to
virtmem - see _bigfile.h for details.

ZBigFile will use this to hook into using WCFS.