Add option for autounmount

Even though filesystem notifications aren't implemented for FUSE, I decided to
try my hand at implementing the autounmount feature (#128). I based it on the
EncFS autounmount code, which records filesystem accesses and checks every X
seconds whether it's idled long enough to unmount.

I've tested the feature locally, but I haven't added any tests for this flag.
I also haven't worked with Go before. So please let me know if there's
anything that should be done differently.

One particular concern: I worked from the assumption that the open files table
is unique per-filesystem. If that's not true, I'll need to add an open file
count and associated lock to the Filesystem type instead.

https://github.com/rfjakob/gocryptfs/pull/265

1 files changed, 8 insertions, 0 deletions

diff --git a/internal/openfiletable/open_file_table.go b/internal/openfiletable/open_file_table.go
index e21c96d..4a8ce28 100644
--- a/internal/openfiletable/open_file_table.go
+++ b/internal/openfiletable/open_file_table.go
@@ -112,3 +112,11 @@ func (c *countingMutex) Lock() {
 func WriteOpCount() uint64 {
 	return atomic.LoadUint64(&t.writeOpCount)
 }
+
+// CountOpenFiles returns how many entries are currently in the table
+// in a threadsafe manner.
+func CountOpenFiles() int {
+	t.Lock()
+	defer t.Unlock()
+	return len(t.entries)
+}