Re: [PATCH 3/8] bdi: add a ->dev_name field to struct backing_dev_info

[Christoph Hellwig <hch@lst.de>]

On Mon, Apr 20, 2020 at 01:41:57PM +0200, Hans de Goede wrote:
> AFAICT for vboxsf the bdi-name can be anything as long as it is unique, hence
> the "vboxsf-" prefix to make this unique vs other block-devices and the
> ".%d" postfix is necessary because the same export can be mounted multiple
> times (without using bind mounts), see:
> https://github.com/jwrdegoede/vboxsf/issues/3

Shouldn't vboxsf switch to get_tree_single instead of get_tree_nodev?
Having two independent dentry trees for a single actual file system
can be pretty dangerous.

>
> The presence of the source inside the bdi-name is only for informational
> purposes really, so truncating that should be fine, maybe switch to:
>
> "vboxsf%d-%s" as format string and swap the sbi->bdi_id and fc->source
> in the args, then if we truncate anything it will be the source (which
> as said is only there for informational purposes) and the name will
> still be guaranteed to be unique.

Can we just switch to vboxsf%d where %d іs a simple monotonically
incrementing count?  That is what various other file systems (e.g. ceph)
do.