Feature #7939

Updated by Brett Smith about 4 years ago

Today, arv-mount daemonizes very early, before it initializes FUSE or makes any API calls. If those later steps fail, arv-mount will not give the user any indication of that. They'll just see that nothing is actually mounted. Examples of things that can go wrong:

* The user doesn't have permission to use FUSE
* The user specified @--allow-other@ but @user_allow_other@ is not set in @/etc/fuse.conf@
* The user has a bad Arvados client configuration (wrong API server; invalid API token)
* The user tried to mount a collection that they can't read

When nothing can be mounted as a consequence of user or administrator error, that error should be reported on stderr, and arv-mount should exit nonzero, so the user immediately knows that there's been a problem, and ideally gets details about what that problem is. For the scope of this story, errors from uncaught exceptions are fine. Obviously we want better error reporting, but that can happen in a later story.

We've tried to fix this in the past, but it's non-trivial because our daemonization code closes all file descriptors by default, and FUSE initialization opens @/dev/fuse@, with no apparent API to find the file descriptor it's using. See commit:f573c35a8f.

Fix:

* Never daemonize (call @self.daemon_ctx.open@) until we're about
If you do find a way to call llfuse.main().
* When we construct the DaemonContext,
find that file descriptor, you can pass @preserve_files=range(3, number of inodes limit)@. Anything arv-mount opens, we trust it in the @preserve_files@ argument list to @daemon.DaemonContext@, and then daemonize just before @llfuse.main()@. If you do this, you'll also need after daemonization.
* Ensure that,
to pass in cases where we know we need to open a specific collection, we do that before daemonization. the file descriptor for the user's log file, if any.

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