fusefs: kernel-based implementation of auto_unmount

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Summary

As it was suggested in D51549 here goes an attempt to implement the auto_unmount feature from within the kernel.

Corresponding libfuse changes are there: https://github.com/libfuse/libfuse/compare/master...arrowd:libfuse:kernel-bsd-auto-unmount

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• Fix hang by marking fdata dead

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I have fixed the hang, but the filesystem still does not get unmounted.

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• Replace VOP_UNMOUNT with dounmount
• Plunk vfs_ref before to avoid deadlock

This implementation seems to work now

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sys/fs/fuse/fuse_vfsops.c

421

It seems to be too late to arm this flag there. I guess I'll have to set it from userspace.

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• Use cdev destructor to clean up the mount point instead of a .d_close method

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This seems to work now. The change turned out to be surprisingly small.

@asomers Could you take a look?

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Ping.

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Ping.

[asomers]

Wow! This looks much simpler than the original userspace-based implementation. I like it. I wrote some tests, too. I can commit those separately if you like, after you commit the main code. The only thing that's missing is a mention of the new option in mount_fusefs.8 . Could you please add that?

sys/fs/fuse/fuse_ipc.h

243

This is going to conflict with e8449c0e0fcb8a3eb5872cbee5c3dde4b05a5f50 . Easy to resolve.

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• Rebase
• Update the man page

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I can commit those separately if you like, after you commit the main code.

Thank you for following up with tests! I trust you to push them.

[asomers]

Approved, but don't forget to bump the man page's .Dd date.