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, 5 insertions, 0 deletions

diff --git a/internal/fusefrontend/fs.go b/internal/fusefrontend/fs.go
index 1b6941e..c0d6151 100644
--- a/internal/fusefrontend/fs.go
+++ b/internal/fusefrontend/fs.go
@@ -47,6 +47,11 @@ type FS struct {
 	// "gocryptfs -fsck" reads from the channel to also catch these transparently-
 	// mitigated corruptions.
 	MitigatedCorruptions chan string
+	// Track accesses to the filesystem so that we can know when to autounmount.
+	// An access is considered to have happened on every call to encryptPath,
+	// which is called as part of every filesystem operation.
+	// (This flag uses a uint32 so that it can be reset with CompareAndSwapUint32.)
+	AccessedSinceLastCheck uint32
 }
 
 var _ pathfs.FileSystem = &FS{} // Verify that interface is implemented.