When a process forks and execs a new process, the child will not be
interested in the parent's file descriptor to /dev/fuse.
Signed-off-by: Shayan Pooya <shayan@arista.com>

TestUnionFsFdLeak looks at global state of the program, and is flaky:
the splice pool keeps open file descriptors, and its number depends on
how many read threads are scheduled in parallel.

Some versions of FUSE need this; fixes pathfs owner tests.

Inode.Parent() has to take the treeLock before looking
at the parents map.

Fixes https://github.com/hanwen/go-fuse/issues/166

The locking code is not hooked in the fuse/ server code, so this
just exercises the kernel's default locking implementation.

The parent tracking moved into nodefs in
commit 0107672a, so there is no need for
taking that lock anymore.

Go 1.9 uses epoll() for more efficient file I/O. File I/O causes a
call to epoll, and the runtime makes this call take up a GOMAXPROCS
slot.

The FUSE kernel module also supports poll: polling on a file residing
in a FUSE file system causes the kernel to sends a POLL request to the
userspace process.  If the process responds with ENOSYS, the kernel
will stop forwarding poll requests to the FUSE process.

In a test for Go FUSE file systems, it is normal to serve the
filesystem out of the same process that opens files in the file
system. If this happens in Go 1.9, the epoll call can take the only
GOMAXPROCS slot left, leaving the process unable to respond to the
FUSE POLL opcode, deadlocking the process.

This change add support for a magic file "/ .go-fuse-epoll-hack" with
node ID uint64(-1), and on starting up the file system, the library
calls poll() on this file, triggering the POLL opcode before the Go
runtime had a chance to do so.

There are two problem scenarios left:

* File system tests that start I/O before calling WaitMount() still
  risk deadlocking themselves.

* The Linux kernel keeps track of feature support in fuse_conn, which notes

         * The following bitfields are only for optimization purposes
         * and hence races in setting them will not cause malfunction

  if our forced ENOSYS gets lost due to a race condition in the
  kernel, this can still trigger.

Fixes golang/go#21014 and #165

This avoids involving the go 1.9 poller in I/O, which causes hangs, as
the poller does not understand the fcntl(O_NONBLOCK) tweak that we
executed on the pipe's file descriptors.

Fixes #164

The root user can issue the umount syscall and does not need the
fusermount binary. Therefore, it is not necessary to fork and exec a new
process just to run the umount binary.

Golang has a global lock held for forking (See exec_unix.go in the golang
source tree):
"Acquire the fork lock so that no other threads create new fds that are
not yet close-on-exec before we fork."

So it would be best if processes would refrain from forking
unnecessarily.
Signed-off-by: Shayan Pooya <shayan@arista.com>

This fixes 'du'.

Fixes #159.

Fixes #160.

This first race was easy to find and fix in the tests themselves.

It exposes another race in nodefs.FileSystemConnector where a node's
mount (and therefore, treeLock) is is not the same as the grand-parent
node's is.

Updates #138.

Fixes #134

Change-Id: I04eb8c16d45dbeef872036aab4091741b981505c

Fixes #127.

This enhances nodes which embed defaultNode (which is most of them),
allowing those implementations to omit a GetAttr() method. Without this,
when the kernel calls GetAttr() for an open file, FUSE will return a
size of zero, causing a read() of the file to always return 0, even
though fuse returns a nonzero number of bytes.

One can leverage this behavior to create a Linux procfs-like file, which
stat shows to be zero bytes, but can be successfully read.

N.B. This behavior is only useful if the FileSystemConnector Options
specify AttrTimeout of zero. Otherwise, the result of the first call to
GetAttr() (file == nil) is cached, and the kernel allows zero bytes to
be read. With this caching disabled, the next GetAttr() call (file !=
nil) will be used to control the number of readable bytes.

1) Fix the "a" instead of "m" typo in loopbackFile.Utimens.
   Besides the incorrect behavoir, this causes a crash if "a"
   is nil.
   Obsoletes https://github.com/hanwen/go-fuse/pull/100 .

2) Enable nanosecond resolution for dates after 1970.
   syscall.NsecToTimespec is broken for dates before 1970 but
   works fine otherwise, so let's keep the nanoseconds there.

3) Deduplicate the time conversion code in nodefs and paths into
   the new function fuse.UtimeToTimespec.

4) Add a test case.

Panic if we insert invalid branchResult into the cache.

Should provide more data for bug #109.

Ensure all.bash tests compilation on both Darwin and Linux.

Fixes #125.

This makes it evident which tests leak mount points.

Move shared test utilities into internal/testutil/ package.

This is less overhead, and fixes the darwin tests that use InitIn.

Fixed handling of ENOSYS in unionfs.

When mounting using relative paths, "touch" on directories
used to fail.

"touch" on files works accidentially because it uses a
file descriptor internally.

  $ loopback b a &
  $ cd b
  $ mkdir foo
  $ touch foo
  touch: setting times of 'foo': Not a directory

strace:

  [pid 30185] utimensat(0, "a/foo", [{1468441847, 0}, {1468441847, 0}], AT_SYMLINK_NOFOLLOW <unfinished ...>
  [pid 30185] <... utimensat resumed> )   = -1 ENOTDIR (Not a directory)