Filesystems usually show the underlying device in the first
column of df. Follow suite and show the original dir, making
"df" and "mount" output more useful.

The actual reason for this change, however, is that it facilitates
running xfstests against go-fuse loopback. The xfstests machinery
checks that the expected device is mounted at the right place.

Commit https://github.com/rfjakob/fuse-xfstests/commit/182841fea487419f493d9b547bf703bee9e39322
adds support for go-fuse loopback to xfstests and depends on this
change.

Before:

  $ df -T
  Filesystem                 Type           1K-blocks       Used Available Use% Mounted on
  loopback                   fuse.loopback  237371192  149885928  75357828  67% /home/jakob/go/src/github.com/hanwen/go-fuse/example/loopback/b

After:

  $ df -T
  Filesystem                 Type           1K-blocks       Used Available Use% Mounted on
  a                          fuse.loopback  237371192  150332024  74911732  67% /home/jakob/go/src/github.com/hanwen/go-fuse/example/loopback/b

Change-Id: I3d5a2e7ab021af4eed657e66654b636e08292219

Per default, "rawBridge" is shown here, which does not tell the user
much about the filesystem. Set to "loopback" as shown below.

Before:

  $ df -T
  Filesystem                 Type            1K-blocks       Used Available Use% Mounted on
  rawBridge                  fuse.rawBridge  237371192  149873220  75370536  67% /home/jakob/go/src/github.com/hanwen/go-fuse/example/loopback/b

After:

  $ df -T
  Filesystem                 Type           1K-blocks       Used Available Use% Mounted on
  loopback                   fuse.loopback  237371192  149885928  75357828  67% /home/jakob/go/src/github.com/hanwen/go-fuse/example/loopback/b

Change-Id: Iaaa18b4193b31567f6589669e8c443715afbd362

Add posix.LinkUnlinkRename to test this behavior; this is the approach
that git uses for writing pack files.

Thanks to Nicola Girardi <idrarig.alocin@gmail.com> for reporting this
bug.

Change-Id: Idb34e32f1dbb3c6c617aa82e29c4f0ac6f8a544d

Change-Id: Ie50ade19cf86abbbc6d6d5710f26ca03d7873098

Failure was:

    zipfs_test.go:74: got block count 8, want 1

This got broken by "fs: set Blksize and Blocks automatically based on Size",
fix it by setting Blksize.

Change-Id: I1d3798082b2e8a7fcda908b9b88d8b51fb11da78

Change-Id: I272909148667e1f0246914ef7fdd1052bf3b5bc3

Change-Id: I1c098b6c06ab62aa7877e47aa3d99f37e9a83e5c

Change-Id: Iac5c1a8329ceb0d8538029bd737cfede2af4d9a2

Change-Id: I811c6a070bfdc3582da816f302354f4a7516beab

Change-Id: I7dfd919df765679bf9c09ec74cefc6c53bfc56b3

Travis CI appears to be too slow for the race detector. 

Change-Id: I5f4e7dc379938cf8000ab2d8ba95e09fab8ed6c9

Pool.Get() can trigger a GC, and we see this GC being hung in stack
traces for the TestDeleteNotify test case.

See issue #261.

Change-Id: I278a05fc3c6a59c701686aebd410511c5502d9d5

Reported-by: Philipp Gillé
Change-Id: I3db9f54016c17744bafa57a813531a99c01e47fa

The API is poorly thought out, as a node can be child in multiple
parents with the same name. Similary, a reversing keys and values is
not possible. A child may have the same parent with different names.

Change-Id: I3888606016b56f06d80ef56ebc7b8725a819c1a9

Change-Id: I451f56511a2b796c6a90df49e6c288d6675af363

Change-Id: I9d9e7a098c0b2de29aad78a6938e39867522f919

Change-Id: Ie5c189f220ebebaf7da8813d9092649619fb2b8d

This makes the default setting more useful.

Change-Id: Iab40ad0ab0e2c9b75b786a883f6ad989178ee5b5

Change-Id: I3464790cd8fd05a4f0e787a3895bf3e81569b29a

This speeds them up, and avoids writing to log files, decreasing
chances of flakiness.

Change-Id: I2a8f254d085303143285d2812e297e879d145652

Change-Id: I71cd7cb713c7e864305ebad73a1b072395c13b27

This simplifies writing R/O filesystems, which do not need flushing.

Change-Id: I428627799904e30f486ff82bcafe2f9c4db88d01

Change-Id: Iaf012013f81c29faeb84f4096dd31d5b6d58e0f5

Change-Id: I87db804ce6df8b21f4cfba8557395b0067a177da

Add dynamic_example_test.go to Readdir/Lookup.

Change-Id: If7cd2a29166b9952af0ca362cba89df1d98b634b

Change-Id: I36aea1eee9937fab4d33657ca4514866750ac55a

Change-Id: I1fe9bf5c77a332002b3b0a15b75853102549b511

Change-Id: Iffe9bf5c77a332002b3b0a15b75853102549b511

Change-Id: Iefe9bf5c77a332002b3b0a15b75853102549b511

In cooperation with GerritHub, a repo-specific deploy key was setup,
which avoids granting blanket r/w access to the Gerrithub server.

This reverts commit 09a2813e.

Change-Id: I09a2813e

This apparently happens in NFS mounts of FUSE file systems when
combined with lots of FS activity. Maybe some part of the client is
caching readdir results in the wrong way?

In any event, returning OK (signifying EOF on the dirstream) is
harmless.

Change-Id: Ib09d77eae0f1af8bce46b07f386fdda20b2ccb95

This complements commit "fuse: allow filesystems to disable
CAP_AUTO_INVAL_DATA" and teaches go-fuse to request explicit data cache
invalidation mode if fuse.MountOptions.ExplicitDataCacheControl is set.

See https://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git/commit/?id=ad2ba64dd489
and https://lwn.net/ml/linux-fsdevel/20190315212556.9315-1-kirr%40nexedi.com/ for rationale and details.

This test was flaky even before ce2558b4 (fuse/test: disable
TestFopenKeepCache) because after file change it was reporting to kernel
both different size (before=6, after=5) and potentially different mtime.
The kernel is known to invalidate file's data cache on size change, and
also to invalidate file's data cache on mtime change if
CAP_AUTO_INVAL_DATA was negotiated at FUSE handshake. Until recently
go-fuse was always using CAP_AUTO_INVAL_DATA mode.

The test was somehow passing on kernels < Linux 4.20 due to the fact
that the write was coming soon after previous lookup/getattr and thus
likely before attributes timeout. The kernel was still seeing old mtime
and size and was not invalidating file cache. If I add just "sleep
enough time for file attributes to expire..." + followup stat from the
patch, the test fails reliably even on older kernels where it used to be
passing:

	=== RUN   TestFopenKeepCache
	17:44:33.397329 rx 1: INIT i0 {7.27 Ra 0x20000 SPLICE_READ,HANDLE_KILLPRIV,IOCTL_DIR,READDIRPLUS,PARALLEL_DIROPS,ABORT_ERROR,POSIX_LOCKS,DONT_MASK,SPLICE_WRITE,SPLICE_MOVE,ASYNC_READ,FLOCK_LOCKS,WRITEBACK_CACHE,POSIX
	17:44:33.397413 tx 1:     OK, {7.23 Ra 0x20000 ASYNC_READ,NO_OPEN_SUPPORT,BIG_WRITES,AUTO_INVAL_DATA,READDIRPLUS,PARALLEL_DIROPS 0/0 Wr 0x10000 Tg 0x0}
	17:44:33.398589 rx 2: LOOKUP i1 [".go-fuse-epoll-hack"] 20b
	17:44:33.398644 tx 2:     2=no such file or directory, {i0 g0 tE=0s tA=0s {M00 SZ=0 L=0 0:0 B0*0 i0:0 A 0.000000 M 0.000000 C 0.000000}}
	17:44:33.398686 rx 3: CREATE i1 {0100100 [WRONLY,TRUNC,CREAT,0x8000] (022)} [".go-fuse-epoll-hack"] 20b
	17:44:33.398710 tx 3:     OK, {i18446744073709551615 g0 {M0100644 SZ=0 L=1 0:0 B0*0 i0:18446744073709551615 A 0.000000 M 0.000000 C 0.000000} &{18446744073709551615 0 0}}
	17:44:33.398745 rx 4: POLL i18446744073709551615
	17:44:33.398753 tx 4:     38=function not implemented
	17:44:33.399446 rx 5: FLUSH i18446744073709551615 {Fh 18446744073709551615}
	17:44:33.399466 tx 5:     5=input/output error
	17:44:33.399540 rx 6: RELEASE i18446744073709551615 {Fh 18446744073709551615 WRONLY,0x8000  L0}
	17:44:33.399548 tx 6:     5=input/output error
	17:44:33.399567 rx 7: LOOKUP i1 ["file.txt"] 9b
	17:44:33.399648 tx 7:     OK, {i3 g2 tE=1s tA=0.01s {M0100644 SZ=6 L=1 1000:1000 B8*4096 i0:841351 A 1552833873.399069 M 1552833873.399069 C 1552833873.399069}}
	17:44:33.399936 rx 8: OPEN i3 {O_RDONLY,0x8000}
	17:44:33.399976 tx 8:     OK, {Fh 2 CACHE}
	17:44:33.400045 rx 9: READ i3 {Fh 2 [0 +4096)  L 0 NONBLOCK,0x8000}
	17:44:33.400065 tx 9:     OK,  4096b data (fd data)
	17:44:33.400185 rx 10: GETATTR i3 {Fh 2}
	17:44:33.400261 tx 10:     OK, {tA=0.01s {M0100644 SZ=6 L=1 1000:1000 B8*4096 i0:841351 A 1552833873.399069 M 1552833873.399069 C 1552833873.399069}}
	17:44:33.400296 rx 11: FLUSH i3 {Fh 2}
	17:44:33.400305 tx 11:     OK
	17:44:33.400324 rx 12: RELEASE i3 {Fh 2 NONBLOCK,0x8000  L0}
	17:44:33.400334 tx 12:     OK

		sleep here

	17:44:33.500843 rx 13: GETATTR i3 {Fh 0}
	17:44:33.500939 tx 13:     OK, {tA=0.01s {M0100644 SZ=5 L=1 1000:1000 B8*4096 i0:841351 A 1552833873.399069 M 1552833873.399069 C 1552833873.399069}}
	17:44:33.501118 rx 14: OPEN i3 {O_RDONLY,0x8000}
	17:44:33.501195 tx 14:     OK, {Fh 2 CACHE}
	17:44:33.501468 rx 15: READ i3 {Fh 2 [0 +4096)  L 0 NONBLOCK,0x8000}
	17:44:33.501500 tx 15:     OK,  4096b data (fd data)
	17:44:33.501582 rx 16: GETATTR i3 {Fh 2}
	17:44:33.501625 tx 16:     OK, {tA=0.01s {M0100644 SZ=5 L=1 1000:1000 B8*4096 i0:841351 A 1552833873.499071 M 1552833873.399069 C 1552833873.399069}}
	17:44:33.502176 rx 17: FLUSH i3 {Fh 2}
	17:44:33.502210 tx 17:     OK
	17:44:33.502268 rx 18: RELEASE i3 {Fh 2 NONBLOCK,0x8000  L0}
	17:44:33.502296 tx 18:     OK
	17:44:33.547469 received ENODEV (unmount request), thread exiting
	17:44:33.547471 received ENODEV (unmount request), thread exiting
	17:44:33.547469 received ENODEV (unmount request), thread exiting
	--- FAIL: TestFopenKeepCache (0.15s)
	    cache_test.go:147: ReadFile: got "after", want cached "before"

In other words the test was racy and was passing only due to likely
conditions to win a race in particular environment. Here is example debug trace
when that particular conditions are met:

	17:52:00.119419 rx 7: LOOKUP i1 ["file.txt"] 9b
	17:52:00.119818 tx 7:     OK, {i3 g2 tE=1s tA=0.01s {M0100644 SZ=6 L=1 1000:1000 B8*4096 i0:853832 A 1552834320.116131 M 1552834320.116131 C 1552834320.116131}}
	17:52:00.122865 rx 8: OPEN i3 {O_RDONLY,0x8000}
	17:52:00.122889 tx 8:     OK, {Fh 2 CACHE}
	17:52:00.122933 rx 9: READ i3 {Fh 2 [0 +4096)  L 0 NONBLOCK,0x8000}
	17:52:00.122957 tx 9:     OK,  4096b data (fd data)
	17:52:00.123014 rx 10: GETATTR i3 {Fh 2}
	17:52:00.123031 tx 10:     OK, {tA=0.01s {M0100644 SZ=6 L=1 1000:1000 B8*4096 i0:853832 A 1552834320.116131 M 1552834320.116131 C 1552834320.116131}}
	17:52:00.123050 rx 11: FLUSH i3 {Fh 2}
	17:52:00.123056 tx 11:     OK
	17:52:00.123071 rx 12: RELEASE i3 {Fh 2 NONBLOCK,0x8000  L0}
	17:52:00.123082 tx 12:     OK

	17:52:00.123105 rx 13: OPEN i3 {O_RDONLY,0x8000} 		<-- NOTE: OPEN, but no GETATTR around
	17:52:00.123124 tx 13:     OK, {Fh 2 CACHE}
	17:52:00.123146 rx 14: FLUSH i3 {Fh 2}
	17:52:00.123152 tx 14:     OK
	17:52:00.123164 rx 15: RELEASE i3 {Fh 2 NONBLOCK,0x8000  L0}
	17:52:00.123183 tx 0:     NOTIFY_INVAL_ENTRY, {parent i1 sz 8} "file.txt"
	17:52:00.123186 tx 15:     OK

However starting from Linux 4.20 the kernel started to always issue
GETATTR request around second OPEN, for example:

	18:34:22.323238 rx 26: LOOKUP i1 ["file.txt"] 9b
	18:34:22.323309 tx 26:     OK, {i3 g2 tE=1s tA=1s {M0100644 SZ=6 L=1 1000:1000 B8*4096 i0:1531145 A 1550252062.321237 M 1550252062.321237 C 1550252062.321237}}
	18:34:22.323339 rx 28: OPEN i3 {O_RDONLY,0x8000}
	18:34:22.323384 tx 28:     OK, {Fh 2 CACHE}
	18:34:22.323441 rx 30: READ i3 {Fh 2 [0 +4096)  L 0 NONBLOCK,0x8000}
	18:34:22.323477 tx 30:     OK,  4096b data (fd data)
	18:34:22.323534 rx 32: FLUSH i3 {Fh 2}
	18:34:22.323546 tx 32:     OK
	18:34:22.323577 rx 34: RELEASE i3 {Fh 2 NONBLOCK,0x8000  L0}
	18:34:22.323594 tx 34:     OK
	18:34:22.323611 rx 36: OPEN i3 {O_RDONLY,0x8000}		<-- NOTE: OPEN with GETATTR around
	18:34:22.323636 tx 36:     OK, {Fh 2 CACHE}
	18:34:22.323661 rx 38: GETATTR i3 {Fh 0}
	18:34:22.323684 tx 38:     OK, {tA=1s {M0100644 SZ=5 L=1 1000:1000 B8*4096 i0:1531145 A 1550252062.322237 M 1550252062.322237 C 1550252062.322237}}
	18:34:22.323729 rx 40: READ i3 {Fh 2 [0 +4096)  L 0 NONBLOCK,0x8000}
	18:34:22.323740 tx 40:     OK,  4096b data (fd data)

which almost always triggers conditions to invalidate data cache on kernel side
(different size and different mtime).

The kernel is not doing anything wrong here - it is allowed to issue
GETATTR request at any time. It is thus only a kernel behaviour change,
still being valid from FUSE protocol point of view, not a kernel
regression.

-> Fix the test

- by disabling CAP_AUTO_INVAL_DATA via ExplicitDataCacheControl. This
  should stop kernel from dropping data cache on mtime change;
- by using the same size for before and after states. This avoid hitting
  cache being dropped when kernel sees file size being changed.

Make the test more picky trying to hit the pain points:

- make sure that mtime of file.txt at before and after states are
  different. Without added sleep the panic on mtime δ == 0 is triggered
  reliably on my notebook.
- issue explicit stat before second open to force kernel to
  relookup/regetattr the file and reread the attributes.

Hopefully finally fixes https://github.com/hanwen/go-fuse/issues/168.

We have many calls to ioutil.WriteFile and ioutil.ReadFile + checking
for error. Move those calls into utility functions which call t.Fatal if
they see any error. No need to use additional error prefix as both
ioutil.WriteFile and ReadFile produce os.PathError which always has
opertion and path on which it was performed.

Add nodefs.Mount - utility to mount root over mountpoint with given
options. We already had nodefs.MountRoot, but that was taking only
nodefs.Options and there was no way to pass fuse.MountOptions in. The
new utility accepts both fuse.MountOptions and nodefs.Options, each
covering their level.

This should be generally useful(*), as well as it will be used in a next
patch in TestFopenKeepCache where fuse.MountOptions.PreciseDataCacheControl
will need to be used.

(*) see e.g. https://lab.nexedi.com/kirr/wendelin.core/blob/8f497094/wcfs/misc.go#L258
as example that users unroll their Mount versions to be able to pass in
fuse.MountOptions.

CAP_AUTO_INVAL_DATA is capability of kernel, but from the point of view
of a filesystem it is not a capability, but a behaviour request: if set,
it requests to kernel - filesystem client - to perform data cache
invalidations based on heuristics. Current heuristic is to drop data
cache for a file if kernel sees file's mtime being changed:

	https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/fuse/inode.c?id=v5.0-0-g1c163f4c7b3f#n238
	https://git.kernel.org/linus/eed2179efe

However this could be unwanted behaviour if filesystem is careful to
explicitly invalidate local file cache: despite filesystem attempts to
preciously keep data cache, the whole cache of the file is unnecessarily
dropped.

-> To fix add a new mount options for filesystems to indicate they are
careful with respect to data cache invalidations and thus should be
fully responsible for invalidating data cache. Teach go-fuse to not send
CAP_AUTO_INVAL_DATA in this mode to kernel on FUSE handshake.

Note, as of upcoming Linux 5.1 (estimated to be released mid 2019), FUSE
client in kernel still automatically and unconditionally drops whole
data cache of a file if its sees size change. Kernel and go-fuse patches
to fix that are here:

	https://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git/commit/?id=ad2ba64dd489
	https://github.com/hanwen/go-fuse/pull/273

The kernel patch is likely to enter mainline kernel when 5.2 merge
window opens. We'll remove XXX in a follow-up go-fuse patch that adds
support for CAP_EXPLICIT_INVAL_DATA.