Disk sync at shutdown and fusefs filesystems

[Alejandro Pulver]

Hello.

The port fusefs-ntfs (NTFS-3G is the official name) is a NTFS
read/write driver using FUSE (a user-space kernel independent API for
writing filesystem drivers). The latter uses a (user-space) cache for
improving performance as there isn't a block device cache in the
kernel, and it was originally made in Linux with that assumption.

The problem with NTFS-3G (and all other FUSE based drivers maybe) is
that it doesn't flush the cache data to the disk at shutdown, but it
does when unmounted (and I guess this doesn't happen automatically). I
noticed this when files I write before manually unmounting persist, and
otherwise sometimes they don't.

So I guess with native (here I mean written directly for the system kernel,
using the kernel cache) FreeBSD filesystems the kernel flushes the cache at
shutdown, but they aren't unmounted.

Generally this isn't a problem since most FUSE filesystems are
"virtual" (for example: over SSH, FTP, HTTP, etc.) and don't use cache
nor need flushing. But this isn't the case with NTFS-3G.

Are my assumptions right? Then I have to look for some way to manually
unmount FUSE filesystems at shutdown, because they are already mounted
at startup. I thought about instructing the fusefs-kmod rc.d script to
unmount FUSE filesystems before attempting to unload the kernel module
(currently it only loads/unloads fuse.ko).

Thanks and Best Regards,
Ale
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