Re: [PATCH RFC v2 00/19] fuse: fuse-over-io-uring

[Kent Overstreet <kent.overstreet@linux.dev>]

On Wed, Jun 12, 2024 at 03:53:42PM GMT, Bernd Schubert wrote:
> I will definitely look at it this week. Although I don't like the idea
> to have a new kthread. We already have an application thread and have
> the fuse server thread, why do we need another one?

Ok, I hadn't found the fuse server thread - that should be fine.

> > 
> > The next thing I was going to look at is how you guys are using splice,
> > we want to get away from that too.
> 
> Well, Ming Lei is working on that for ublk_drv and I guess that new approach
> could be adapted as well onto the current way of io-uring.
> It _probably_ wouldn't work with IORING_OP_READV/IORING_OP_WRITEV.
> 
> https://lore.gnuweeb.org/io-uring/20240511001214.173711-6-ming.lei@redhat.com/T/
> 
> > 
> > Brian was also saying the fuse virtio_fs code may be worth
> > investigating, maybe that could be adapted?
> 
> I need to check, but really, the majority of the new additions
> is just to set up things, shutdown and to have sanity checks.
> Request sending/completing to/from the ring is not that much new lines.

What I'm wondering is how read/write requests are handled. Are the data
payloads going in the same ringbuffer as the commands? That could work,
if the ringbuffer is appropriately sized, but alignment is a an issue.

We just looked up the device DMA requirements and with modern NVME only
4 byte alignment is required, but the block layer likely isn't set up to
handle that.

So - prearranged buffer? Or are you using splice to get pages that
userspace has read into into the kernel pagecache?