Summary:
The higher level goal is to make it easier to deal
with the graceful restart scenario.
This diff removes the SessionDeleter class and effectively renames
the Channel class to FuseChannel. The FuseChannel represents
the channel to the kernel; it can be constructed from a fuse
device descriptor that has been obtained either from the privhelper
at mount time, or from the graceful restart procedure. Importantly
for graceful restart, it is possible to move the fuse device
descriptor out of the FuseChannel so that it can be transferred
to a new eden process.
The graceful restart procedure requires a bit more control over
the lifecycle of the fuse event loop so this diff also takes over
managing the thread pool for the worker threads. The threads
are owned by the MountPoint class which continues to be responsible
for starting and stopping the fuse session and notifying EdenServer
when it has finished. A nice side effect of this change is that
we can remove a couple of inelegant aspects of the integration;
the stack size env var stuff and the redundant extra thread
to wait for the loop to finish.
I opted to expose the dispatcher ops struct via an `extern` to
simplify the code in the MountPoint class and avoid adding special
interfaces for passing the ops around; they're constant anyway
so this doesn't feel especially egregious.
Reviewed By: bolinfest
Differential Revision: D5751521
fbshipit-source-id: 5ba4fff48f3efb31a809adfc7787555711f649c9
