On Wed, Jun 12, 2024 at 06:15:57PM GMT, Bernd Schubert wrote: > > > On 6/12/24 17:55, Kent Overstreet wrote: > > On Wed, Jun 12, 2024 at 03:40:14PM GMT, Bernd Schubert wrote: > > > On 6/12/24 16:19, Kent Overstreet wrote: > > > > 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@xxxxxxxxxx/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. > > > > > > That is exactly the big discussion Miklos and I have. Basically in my > > > series another buffer is vmalloced, mmaped and then assigned to ring entries. > > > Fuse meta headers and application payload goes into that buffer. > > > In both kernel/userspace directions. io-uring only allows 80B, so only a > > > really small request would fit into it. > > > > Well, the generic ringbuffer would lift that restriction. > > Yeah, kind of. Instead allocating the buffer in fuse, it would be now allocated > in that code. At least all that setup code would be moved out of fuse. I will > eventually come to your patches today. > Now we only need to convince Miklos that your ring is better ;) > > > > > > Legacy /dev/fuse has an alignment issue as payload follows directly as the fuse > > > header - intrinsically fixed in the ring patches. > > > > *nod* > > > > That's the big question, put the data inline (with potential alignment > > hassles) or manage (and map) a separate data structure. > > > > Maybe padding could be inserted to solve alignment? > > Right now I have this struct: > > struct fuse_ring_req { > union { > /* The first 4K are command data */ > char ring_header[FUSE_RING_HEADER_BUF_SIZE]; > > struct { > uint64_t flags; > > /* enum fuse_ring_buf_cmd */ > uint32_t in_out_arg_len; > uint32_t padding; > > /* kernel fills in, reads out */ > union { > struct fuse_in_header in; > struct fuse_out_header out; > }; > }; > }; > > char in_out_arg[]; > }; > > > Data go into in_out_arg, i.e. headers are padded by the union. > I actually wonder if FUSE_RING_HEADER_BUF_SIZE should be page size > and not a fixed 4K. I would make the commands variable sized, so that commands with no data buffers don't need padding, and then when you do have a data command you only pad out that specific command so that the data buffer starts on a page boundary.
