Make LoopbackNode and LoopbackRoot public, and add an example of how
to extend them.

Fixes #364.

Change-Id: Idcce1bf3765e93ece3bcf9d14de8a957b8c6b63a

Closes #379.

Change-Id: Ieb821fe7e68a3b7822306ad620dcdf834b5dfc12

Document LoopbackNode, LoopbackRoot. Use loopbackRoot.newNode() for
creating new nodes

Change-Id: I625c7706

Change-Id: I19d52f14f63f1481b2b1aa9dcd46c91fe4e1ad99

This leaves only one type to implement for the loopback file system,
which will simplify extending the loopback functionality.

Change-Id: I8906755f3bdf2ea63557d5bb25f50651521364c7

This provides a test for GitHub PR #378, ie. the previous commit

Change-Id: I9473722e

Change-Id: I8845cac5c18d2640b46971564f94f7ff1741a0ee

On OSX, syscall.O_TRUNC on the Create call apparently triggers a
SETATTR call with size 0, which must be responded to correctly.

Change-Id: Icb99891eae99ced6ffbd5fb1dadf42ffad687534

Some of the error codes due to the poll hack get returned back to the
OSX mount process, which leads to failing mounts.

Change-Id: I5b10509c3b8173343caf3f67c0e12a25ddfae32b

syscall.Dirent declares a 256-byte "name" field. In reality, this
field is only as long as necessary to transmit the name, so more
entries can be packed in a page.

When casting the result to syscall.Dirent, the result might run over
the end of the byte buffer, which the race detector doesn't like.

Address this by using our own flavor of syscall.Dirent. All linux
flavors use the same structure layout, except for the amount of
padding at the end.

Change-Id: I618f7ef9e167894e1ab25b2113dcd20d7b76ceb4

nodeid and inode number used to be identical, which is
why both could be marked as "iXXX". This is no longer the
case, so make nodeids distinguishable.

Example:

23:47:17.637736 rx 9156: MKDIR n28 {0777 (00)} ["d90X"] 5b
23:47:17.637801 tx 9156:     OK, {n112 g1 tE=1s tA=1s {M040755 SZ=4096 L=2 1026:1026 B8*4096 i0:2769795 A 1601761637.637385 M 1601761637.637385 C 1601761637.637385}}

v4: also update orphaned inode warning

Change-Id: Ib29dabfd4cf6692cf4118191f8dc73529562426f

Using the inode numbers as the nodeid causes problems
when the fs reuses inode numbers. This is the case with
any overlay filesystem that is backed by ext4 like the
loopback example or gocryptfs.

We already had the expSleep() and re-add hack,

	7090b027 fs: wait out apparent inode type change
	68f70527 fs: addNewChild(): handle concurrent FORGETs

to mitigate some of the problems (at the risk of deadlocking
forever), but I could not find a way to work around the following
case uncovered by fsstress:

The kernel expects a fresh nodeid from MKDIR (see #372 for a
debug log).

This is now guaranteed by passing the O_EXCL to addNewChild().
However, this also means that the hard link detection must
happen in addNewChild() as opposed to newInodeUnlocked()
before. The expSleep and re-add hacks are no longer needed
and have been dropped.

This survived 24 hours (42587 iterations) of fsstress testing.
Tested was the loopback example running on top of ext4 on
Linux 5.8.10.

Fixes https://github.com/hanwen/go-fuse/issues/372 .

v2: Rename inoMap -> stableAttrs, nodeidMap -> kernelNodeIds
    acc. to feedback from Han-Wen.
v3: initialize Inode.nodeId early
v4: drop leftover file stash.txt

Change-Id: Ibb36a886f15d48727daa10b9717ea88e45a6b8af

With rename and link, it hangs within 20ms, so we can reduce the
runtime.

Also add deadlock detection & statistics printout.

A good run looks like this:

	$ TMPDIR=/var/tmp go test -run TestFsstress -v
	=== RUN   TestFsstress
	    simple_test.go:601: Operation statistics:
	    simple_test.go:604:      creat:    33 ok, 132978 fail,  0 hung
	    simple_test.go:604:       link:    85 ok,  37196 fail,  0 hung
	    simple_test.go:604:      mkdir:    60 ok, 155273 fail,  0 hung
	    simple_test.go:604:     mkfifo:    45 ok, 161937 fail,  0 hung
	    simple_test.go:604: mknod_fifo:    55 ok, 154459 fail,  0 hung
	    simple_test.go:604:  mknod_reg:    77 ok, 180614 fail,  0 hung
	    simple_test.go:604: mknod_sock:    83 ok, 139479 fail,  0 hung
	    simple_test.go:604:    readdir:    13 ok,      0 fail,  0 hung
	    simple_test.go:604:     remove:   180 ok,     40 fail,  0 hung
	    simple_test.go:604:     rename:   646 ok,    137 fail,  0 hung
	    simple_test.go:604:      rmdir:    48 ok,  48342 fail,  0 hung
	    simple_test.go:604:    symlink:    30 ok, 119954 fail,  0 hung
	    simple_test.go:604:     unlink:   150 ok,   6121 fail,  0 hung

	--- PASS: TestFsstress (1.02s)
	PASS
	ok  	github.com/hanwen/go-fuse/v2/fs	1.022s

A bad run like this:

	go-fuse/fs$ TMPDIR=/var/tmp go test -run TestFsstress -v
	=== RUN   TestFsstress
	    simple_test.go:592: timeout waiting for goroutines to exit (deadlocked?)
	    simple_test.go:601: Operation statistics:
	    simple_test.go:604:      creat:     0 ok,     44 fail, 10 hung
	    simple_test.go:604:       link:     0 ok,      6 fail, 10 hung
	    simple_test.go:604:      mkdir:     1 ok,    283 fail, 10 hung
	    simple_test.go:604:     mkfifo:     1 ok,    140 fail, 10 hung
	    simple_test.go:604: mknod_fifo:     1 ok,   1246 fail, 10 hung
	    simple_test.go:604:  mknod_reg:     0 ok,     19 fail, 10 hung
	    simple_test.go:604: mknod_sock:     0 ok,    110 fail, 10 hung
	    simple_test.go:604:    readdir:     1 ok,      0 fail,  1 hung
	    simple_test.go:604:     remove:     1 ok,      0 fail, 10 hung
	    simple_test.go:604:     rename:     0 ok,     12 fail, 10 hung
	    simple_test.go:604:      rmdir:     1 ok,    346 fail, 10 hung
	    simple_test.go:604:    symlink:     1 ok,   1456 fail, 10 hung
	    simple_test.go:604:     unlink:     2 ok,     15 fail, 10 hung
	    simple_test.go:51: /usr/bin/fusermount: failed to unmount /var/tmp/TestFsstress302646914/mnt: Device or resource busy
	         (code exit status 1)

	--- FAIL: TestFsstress (2.30s)
	FAIL

	[hangs]

Change-Id: I9eb0ce02eb1df766be257d6a87de53c6ffa6d21e

TestFsstress is loosely modeled after xfstest's fsstress. It performs rapid
parallel removes / creates / readdirs. Coupled with inode reuse, this test
used to deadlock go-fuse quite quickly.

Change-Id: Ia3af099e08c74d3c160062c1ed414430b6c1e7c9

If this happens, it means our node accounting is messed up.
Abort the process by panicing instead of wrapping around
to UINT_MAX.

Change-Id: Id662ab03877d44a16785bfd164a96173a3b7519f

If kernel internally serializes lookup requests for a directory, the
test will deadlock, becaue it tries to issue two such request and pause
lookup handlers, untill both requests come in.

For example here is how this test hangs on Ubuntu Xenial 16.04:

kirr@kubu:~/t/go-fuse$ go test -count=1 -v -run TestNodeParallelLookup ./fuse/test/
=== RUN   TestNodeParallelLookup
18:24:38.494651 rx 1: INIT i0 {7.23 Ra 0x20000 POSIX_LOCKS,ATOMIC_O_TRUNC,EXPORT_SUPPORT,DONT_MASK,FLOCK_LOCKS,READDIRPLUS_AUTO,ASYNC_DIO,WRITEBACK_CACHE,SPLICE_WRITE,SPLICE_READ,IOCTL_DIR,AUTO_INVAL_DATA,READDIRPLUS,NO_OPEN_SUPPORT,ASYNC_READ,BIG_WRITES,SPLICE_MOVE}
18:24:38.494713 tx 1:     OK, {7.23 Ra 0x20000 ASYNC_READ,BIG_WRITES,AUTO_INVAL_DATA,READDIRPLUS,NO_OPEN_SUPPORT 0/0 Wr 0x10000 Tg 0x0}
18:24:38.495351 rx 2: LOOKUP i1 [".go-fuse-epoll-hack"] 20b
18:24:38.495467 tx 2:     OK, {i18446744073709551615 g0 tE=0s tA=0s {M0100644 SZ=0 L=1 0:0 B0*0 i0:18446744073709551615 A 0.000000 M 0.000000 C 0.000000}}
18:24:38.495530 rx 3: OPEN i18446744073709551615 {O_RDONLY,0x8000}
18:24:38.495575 tx 3:     OK, {Fh 18446744073709551615 }
18:24:38.495624 rx 4: POLL i18446744073709551615
18:24:38.495659 tx 4:     38=function not implemented
18:24:38.495706 rx 5: FLUSH i18446744073709551615 {Fh 18446744073709551615}
18:24:38.495741 tx 5:     34=numerical result out of range
18:24:38.495812 rx 6: RELEASE i18446744073709551615 {Fh 18446744073709551615 0x8000  L0}
18:24:38.495849 tx 6:     34=numerical result out of range
18:24:38.495904 rx 7: LOOKUP i1 ["world"] 6b
18:24:38.495957 I: <- lookup "world"
< hang >

Amends: 17c0c400 (nodefs: Allow for several Lookup requests to be served simultaneously)
Updates: https://github.com/hanwen/go-fuse/issues/261

Change-Id: I5d0a76d1190af805351326c378f69cf8ff781a37

GOMAXPROCS=1 currently triggers tests hang:
https://github.com/hanwen/go-fuse/issues/261

Change-Id: I3dc98c8bbdaac7a4ce86639e405ba1a1cef4c295

Change-Id: I8291dceac66bd02bc8fbb845d1f125c4cf22f48e

When a filesystem is mounted with the default_permissions mount
option (which you want to do when other users can access the
mount), the kernel issues extra GETATTR calls to determine access
rights. The GETATTR was not handled and pollHack failed with
"numerical result out of range", preventing the mount from succeeding.

Handle GETATTR so mounting with default_permissions works again.

Before:

	$ gocryptfs -fusedebug -extpass "echo test" -ko default_permissions a b
	Reading password from extpass program "echo", arguments: ["test"]
	Decrypting master key
	2020/09/08 19:09:21 rx 2: INIT i0 {7.31 Ra 0x20000 ABORT_ERROR,MAX_PAGES,ATOMIC_O_TRUNC,EXPORT_SUPPORT,READDIRPLUS_AUTO,ASYNC_DIO,NO_OPEN_SUPPORT,PARALLEL_DIROPS,ASYNC_READ,BIG_WRITES,SPLICE_MOVE,WRITEBACK_CACHE,HANDLE_KILLPRIV,NO_OPENDIR_SUPPORT,CACHE_SYMLINKS,EXPLICIT_INVAL_DATA,POSIX_LOCKS,SPLICE_WRITE,SPLICE_READ,IOCTL_DIR,AUTO_INVAL_DATA,READDIRPLUS,DONT_MASK,FLOCK_LOCKS,POSIX_ACL}
	2020/09/08 19:09:21 tx 2:     OK, {7.28 Ra 0x20000 AUTO_INVAL_DATA,READDIRPLUS,NO_OPEN_SUPPORT,PARALLEL_DIROPS,ASYNC_READ,BIG_WRITES 0/0 Wr 0x20000 Tg 0x0}
	2020/09/08 19:09:21 rx 4: GETATTR i1 {Fh 0}
	2020/09/08 19:09:21 tx 4:     OK, {tA=1s {M040755 SZ=80 L=2 1026:1026 B0*4096 i0:1 A 1599584934.254242 M 1599584467.201817 C 1599584467.201817}}
	2020/09/08 19:09:21 rx 6: GETATTR i1 {Fh 0}
	2020/09/08 19:09:21 tx 6:     OK, {tA=1s {M040755 SZ=80 L=2 1026:1026 B0*4096 i0:1 A 1599584934.254242 M 1599584467.201817 C 1599584467.201817}}
	2020/09/08 19:09:21 rx 8: LOOKUP i1 [".go-fuse-epoll-hack"] 20b
	2020/09/08 19:09:21 tx 8:     OK, {i18446744073709551615 g0 tE=0s tA=0s {M0100644 SZ=0 L=1 0:0 B0*0 i0:18446744073709551615 A 0.000000 M 0.000000 C 0.000000}}
	2020/09/08 19:09:21 rx 10: LOOKUP i1 [".Trash"] 7b
	2020/09/08 19:09:21 tx 10:     2=no such file or directory, {i0 g0 tE=1s tA=0s {M00 SZ=0 L=0 0:0 B0*0 i0:0 A 0.000000 M 0.000000 C 0.000000}}
	2020/09/08 19:09:21 rx 12: GETATTR i18446744073709551615 {Fh 0}
	2020/09/08 19:09:21 tx 12:     34=numerical result out of range, {tA=0s {M00 SZ=0 L=0 0:0 B0*0 i0:0 A 0.000000 M 0.000000 C 0.000000}}
	fs.Mount failed: numerical result out of range

After:

	$ gocryptfs -fusedebug -extpass "echo test" -ko default_permissions a b
	Reading password from extpass program "echo", arguments: ["test"]
	Decrypting master key
	2020/09/08 19:21:33 rx 2: INIT i0 {7.31 Ra 0x20000 READDIRPLUS,POSIX_ACL,CACHE_SYMLINKS,SPLICE_WRITE,IOCTL_DIR,AUTO_INVAL_DATA,FLOCK_LOCKS,ASYNC_DIO,HANDLE_KILLPRIV,ABORT_ERROR,ATOMIC_O_TRUNC,BIG_WRITES,DONT_MASK,SPLICE_MOVE,PARALLEL_DIROPS,EXPORT_SUPPORT,SPLICE_READ,READDIRPLUS_AUTO,WRITEBACK_CACHE,NO_OPEN_SUPPORT,ASYNC_READ,POSIX_LOCKS,MAX_PAGES,NO_OPENDIR_SUPPORT,EXPLICIT_INVAL_DATA}
	2020/09/08 19:21:33 tx 2:     OK, {7.28 Ra 0x20000 NO_OPEN_SUPPORT,ASYNC_READ,AUTO_INVAL_DATA,READDIRPLUS,BIG_WRITES,PARALLEL_DIROPS 0/0 Wr 0x20000 Tg 0x0}
	2020/09/08 19:21:33 rx 4: GETATTR i1 {Fh 0}
	2020/09/08 19:21:33 tx 4:     OK, {tA=1s {M040755 SZ=80 L=2 1026:1026 B0*4096 i0:1 A 1599585687.491337 M 1599585688.791343 C 1599585688.791343}}
	2020/09/08 19:21:33 rx 6: GETATTR i1 {Fh 0}
	2020/09/08 19:21:33 tx 6:     OK, {tA=1s {M040755 SZ=80 L=2 1026:1026 B0*4096 i0:1 A 1599585687.491337 M 1599585688.791343 C 1599585688.791343}}
	2020/09/08 19:21:33 rx 8: LOOKUP i1 [".go-fuse-epoll-hack"] 20b
	2020/09/08 19:21:33 tx 8:     OK, {i18446744073709551615 g0 tE=0s tA=0s {M0100644 SZ=0 L=1 0:0 B0*0 i0:18446744073709551615 A 0.000000 M 0.000000 C 0.000000}}
	2020/09/08 19:21:33 rx 10: GETATTR i18446744073709551615 {Fh 0}
	2020/09/08 19:21:33 tx 10:     OK, {tA=0s {M0100644 SZ=0 L=1 0:0 B0*0 i0:18446744073709551615 A 0.000000 M 0.000000 C 0.000000}}
	2020/09/08 19:21:33 rx 12: OPEN i18446744073709551615 {O_RDONLY,0x8000}
	2020/09/08 19:21:33 tx 12:     OK, {Fh 18446744073709551615 }
	2020/09/08 19:21:33 rx 14: POLL i18446744073709551615
	2020/09/08 19:21:33 tx 14:     38=function not implemented
	2020/09/08 19:21:33 rx 16: FLUSH i18446744073709551615 {Fh 18446744073709551615}
	2020/09/08 19:21:33 tx 16:     34=numerical result out of range
	2020/09/08 19:21:33 rx 18: RELEASE i18446744073709551615 {Fh 18446744073709551615 0x8000  L0}
	2020/09/08 19:21:33 tx 18:     34=numerical result out of range
	Filesystem mounted and ready.

Change-Id: Idfaea994ee6a4b8f28acbe8343063f6250cbef35

This provides feedback to file system authors about what we receive
from the kernel. This can help figure out which system is to blame for
data corruption.

Change-Id: I7cd7f340bf705c9972c95cfc6d3d8612f1ce8b34

Use LOOKUP & OPEN instead of CREATE so it also
works on read-only mounts.

go-fuse/fs$ go test -run TestRoMount -v
=== RUN   TestRoMount
20:31:07.892736 rx 2: INIT i0 {7.31 Ra 0x20000 NO_OPEN_SUPPORT,ASYNC_READ,POSIX_LOCKS,EXPORT_SUPPORT,AUTO_INVAL_DATA,SPLICE_MOVE,SPLICE_READ,HANDLE_KILLPRIV,ABORT_ERROR,EXPLICIT_INVAL_DATA,BIG_WRITES,SPLICE_WRITE,READDIRPLUS,WRITEBACK_CACHE,IOCTL_DIR,READDIRPLUS_AUTO,ASYNC_DIO,PARALLEL_DIROPS,ATOMIC_O_TRUNC,DONT_MASK,FLOCK_LOCKS,POSIX_ACL,MAX_PAGES,CACHE_SYMLINKS,NO_OPENDIR_SUPPORT}
20:31:07.892799 tx 2:     OK, {7.28 Ra 0x20000 BIG_WRITES,READDIRPLUS,PARALLEL_DIROPS,ASYNC_READ,AUTO_INVAL_DATA,NO_OPEN_SUPPORT 0/0 Wr 0x10000 Tg 0x0}
20:31:07.892967 rx 4: LOOKUP i1 [".go-fuse-epoll-hack"] 20b
20:31:07.893002 tx 4:     OK, {i18446744073709551615 g0 tE=0s tA=0s {M0100644 SZ=0 L=1 0:0 B0*0 i0:18446744073709551615 A 0.000000 M 0.000000 C 0.000000}}
20:31:07.893030 rx 6: OPEN i18446744073709551615 {O_RDONLY,0x8000}
20:31:07.893037 tx 6:     OK, {Fh 18446744073709551615 }
20:31:07.893053 rx 8: POLL i18446744073709551615
20:31:07.893059 tx 8:     38=function not implemented
20:31:07.893074 rx 10: FLUSH i18446744073709551615 {Fh 18446744073709551615}
20:31:07.893079 tx 10:     34=numerical result out of range
20:31:07.893131 rx 12: RELEASE i18446744073709551615 {Fh 18446744073709551615 0x8000  L0}
20:31:07.893153 tx 12:     34=numerical result out of range
20:31:07.896705 received ENODEV (unmount request), thread exiting
20:31:07.896719 received ENODEV (unmount request), thread exiting
20:31:07.896888 received ENODEV (unmount request), thread exiting

Change-Id: I6de861bdccf03184a4ca3deeefb1cfdc930aabe3
--- PASS: TestRoMount (0.01s)
PASS
ok  	github.com/hanwen/go-fuse/v2/fs	0.015s

Change-Id: Ic66ca153f5b739e5e081988fdc48d51cde5470f0

Currently fails like this

	18:13:57.008805 Mount fail: read-only file system

because pollHack requires write access.

This will be fixed in pollHack in a later commit.

Change-Id: I37b459339eda2e8270ca8094455db3ddbf764911

Also add a test if "ro" works directly in the fs
package.

Currently fails like this (will be fixed later):

	--- FAIL: TestRoMount (0.01s)
	    simple_test.go:116: read-only file syste

Change-Id: I8194360b1d092268784b9c2b17de274b86633aa2

Regression test for https://github.com/hanwen/go-fuse/issues/344
"[v2 API] xfstests generic/257 fails (getdents seek trouble)"

Change-Id: Icefab07f6762f8e56de525713facf992797d4435

"seeking" works by skipping forward to the requested offset,
first rewinding to zero if seeking back.

The performance is obviously bad, however, seeking
inside a directory does not seem to be too common.

I think the solution is good enough until we see a
use case where this causes performance issues.

Fixes https://github.com/hanwen/go-fuse/issues/344

Change-Id: Ia7f7fbffaf932c16919eafede6b70f4aff245c25

Change-Id: Ie2aeb012346b2fbcc32de09ea05b39069291d803

Change-Id: Ife141f38f2b7598223935963e2916b0b9a609cca

Commit d0fca860 introduced big lookup lock with the idea to "make sure
we don't return forgotten nodes to the kernel". However this way it also
started to prevent several Lookup handlers to be running simultaneously,
which can deadlock if e.g. Lookup handler somehow synchronizes with
other thread which caused the lookup:

https://github.com/hanwen/go-fuse/commit/d0fca860#commitcomment-37772099

On the surface the fix is easy: if we need to prevent lookups running in
parallel to forget, we can turn lookupLock into shared one wrt Lookup,
but exclusive wrt Forget.

However a more correct fix would be to review nodefs locking completely:
there is already per-filesystem treeLock RWMutex, which is _already_
used to synchronize for forgets and lookups. From this point of view
lookupLock is unneeded and the correct fix that d0fca860 should have been
doing is to correct the scope of treeLock to be used more precisely.

However that would be a more intrusive change, and given that nodefs is
considered deprecated today, imho it is better to proceed with making
lookupLock a shared one.

The test that is added deadlocks without provided fix.

I suggest not to reject this patch based on rationale that "nodefs is
deprecated" as there still are real filesystems that use nodefs.

I had not reviewed v2 go-fuse/fs locking yet.

Change-Id: I18e01457f474dea31dc17186dfe6db582c2e6337

This used to create a hidden folder in the user's home
directory to avoid /tmp, which is on tmpfs on modern
distros.

Use /var/tmp instead, which is also a real filesystem,
and avoid cluttering the home dir.

Change-Id: Ifa0a1dbdf7a2c4b08e53d20e28f287207ff8ef47

Per default, "go test ./..." tests multiple packages in
parallel.

From "go help build":

	-p n
		the number of programs, such as build commands or
		test binaries, that can be run in parallel.
		The default is the number of CPUs available.

This seems rather innocent, but a consequence of tests
running in parallel is that the all the output of each test
is buffered until it completes. This prevents multiple tests
interleaving their output.

This also means that when a test hangs, we get no output at
all, which is pretty bad.

Disable parallelization and trade test time for better
debugability of hung tests.

Change-Id: I4c670b65baa2df3bef70bce622b830530a316ee7

This gets added on every build and every test run,
dirtying the git tree again and again.

Give in and let Go 1.13 have it's entry in go.mod.

Change-Id: I13679e54fca09ab818bc0167dff3f1ad851e763e

Running `go test ./... -race` showed a data race
at `rootNode.deleted`. This race cannot really happen,
but the race detector does not know that as the calls
go through FUSE an appear to not be synchronized.

Use atomic loads and stores to make the race detector
happy.

Change-Id: I26bd3e7d8efdd5b967fdb360eb17d7f71a8005c8

If "dist" is not specified, Travis uses Ubuntu 16.04
with kernel 4.15.0-1028-gcp. This kernel misses fixes
to FUSE which cause hangs in TestParallelDiropsHang.

Specifying "dist: bionic" makes Travis use kernel
5.0.0-1026-gcp.

Fixes https://github.com/hanwen/go-fuse/issues/281
Change-Id: Ic0f9987726eb11c608ec0cf42b73e089ec1cd2db

Change-Id: If158380a909a6bf78212c75c8dddc57e8c955448

The server.Serve routine can be called both inline and as
goroutine. In the latter case, it is a synchronization error for Serve
to call serve.loops.Add() by itself, leading to a detected race.

Change-Id: I36f24bd36d1ae77d71e7d69a54ebdf5dbee9bd62

The loopback example is usually used to debug and develop.
Enable the new diagnostics logging facility, unless -q (quiet)
is passed.

Change-Id: I9ae5214fc33616656832a219fc1470f421786b8c

Some ".deleted" logic was in place, but did not work
properly when the Inode was in the root directory.

Fix that by introducing the `found` variable and
add a test that verifies that it works.

Also, return `.go-fuse.$RANDOM/deleted` to make it
very unlikely that the placeholder name matches an
actual file or directory. Introducing the `/deleted`
subdir makes sure operations creating a file or
directory fail reliably with ENOENT.

Tests now look like this:

  $ go test ./fs -run TestPosix/RenameOpenDir -count 1  -v
  === RUN   TestPosix
  === RUN   TestPosix/RenameOpenDir
  [...]
  --- PASS: TestPosix (0.01s)
      --- SKIP: TestPosix/RenameOpenDir (0.01s)
          test.go:383: Fstat failed: no such file or directory. Known limitation - see https://github.com/hanwen/go-fuse/issues/55
  PASS
  ok    github.com/hanwen/go-fuse/v2/fs 0.014s

Change-Id: I2eb6fd48a11df543c9b7daf62647cb9d8a892568

The test seemed to pass because the inode number is overridden
in rawBridge.getattr, but looking at the permissions shows that
the wrong directory is stat()ed:

  $ go test ./fs -run TestPosix/RenameOpenDir -count 1  -v
  [...]
  17:49:46.454077 received ENODEV (unmount request), thread exiting
  17:49:46.454343 received ENODEV (unmount request), thread exiting
  --- PASS: TestPosix (0.01s)
      --- SKIP: TestPosix/RenameOpenDir (0.01s)
          test.go:392: got permissions 0755, want 0700. Known limitation - see https://github.com/hanwen/go-fuse/issues/55
  PASS
  ok    github.com/hanwen/go-fuse/v2/fs 0.016s

Also, add a log message whenever the inode number is overridden,
this should (probably) not happen during normal operation. And
it actually only happens once in the test suite (in RenameOpenDir):

  $ go test ./... -count 1 -v 2>&1 | grep "overriding ino"
  14:48:44.143694 warning: rawBridge.getattr: overriding ino 188663 with 186314

See https://github.com/hanwen/go-fuse/issues/55

Change-Id: I8b2ddb84c35a3b28b4f5e032e7113f8d484a5981

Change-Id: I4fabf222a306e5d3abdfda28422b046cd75c9a8c

The type assertion was meant to operate on `f.file`,
not on `n.ops` again.

Fixes xfstests generic/228.

Change-Id: I8f8ca0cead91a512a6d7826dd7e7e5d1887ae627

Set `opts.NullPermissions = true` to stop us from falsifying
file permissions on "000" files.

Fixes xfstests generic/088.

Change-Id: Ibabbdc97b1ae2531ca093bae6bb441ae15d3238e