How to register FUSE filesystem type with mount(8) and fstab?

In general, one "registers" a new mount filesystem type by creating an executable mount.fstype.

$ ln -s /usr/bin/vdbfs.py /usr/sbin/mount.vdbfs

If vdbfs.py takes mount-ish arguments (i.e. dev path [-o opts]), then mount -t vdbfs and using vdbfs as the 3rd field in fstab will work. If it doesn't, you can create a wrapper which does take arguments of that form and maps them to whatever your vdbfs.py takes.

FUSE should also install a mount.fuse executable; mount.fuse 'vdbfs.py#dev' path -o opts will go on and call vdbfs.py dev path -o opts. In that case, you can use fuse as your filesystem type and prefix your device with vdbfs.py#.

So to clarify ephemient's answer, there are two options:

1. Edit /etc/fstab like this:

   # <file system>   <mount point>      <type>  <options>         <dump>  <pass>
   # ...
   vdbfs.py#<dev>    /srv/virtual-db    fuse    user,<other-opts>    0    0
   

   Or,

2. Create an executable prefixed with "mount." (ensuring it can be used with mount-like options):

   $ ln -s /usr/bin/vdbfs.py /usr/sbin/mount.vdbfs
   

   And edit /etc/fstab like this:

   # <file system> <mount point> <type>    <options>         <dump>  <pass>
   # ...
   <dev>    /srv/virtual-db    vdbfs.py    user,<other-opts>    0    0
   

With regards to auto-mounting at start up and manually mounting with mount, the user and noauto options are relevant and fully supported by fuse itself so you don't have to implement them yourself. The user option lets a non-priveleged user who is a member of the "fuse" group mount your filesystem with the mount command, and noauto directs your filesystem not to automatically mount at startup. If you don't specify noauto, it will automatically mount.

To clarify @patryk.beza comment on the accepted answer, the correct way to mount a FUSE file system is by setting the file system type to fuse.<subtype>.

For example, to mount an s3fs-fuse implementation, which does not provide a specific /sbin/mount.* wrapper and uses normally the s3fs user command to mount S3 buckets, one can use this command as root:

mount -t fuse.s3fs bucket-name /path/to/dir -o <some,options>

or this line in /etc/fstab:

bucket-name /path/to/dir fuse.s3fs <some,options> 0 0

or this SystemD mount unit (for example, /etc/systemd/system/path-to-dir.mount):

[Unit]
Description=S3 Storage
After=network.target

[Mount]
What=bucket-name
Where=/path/to/dir
Type=fuse.s3fs
Options=<some,options>

[Install]
WantedBy=multi-user.target

How this works: mount recognizes the concept of "filesystem subtypes" when the type is formatted with a period (i.e. <type>.<subtype>), so that a type with the format fuse.someimpl is recognized to be the responsibility of the FUSE mount helper /sbin/mount.fuse. The FUSE mount helper then resolves the someimpl part to the FUSE implementation, in the same way as the # format is used in the original answer (I think this is just a path search for a program named <subtype>, but I'm not 100% sure about it).