On Tue, May 02, 2023 at 10:57:30PM +0800, Ming Lei wrote: > On Sun, Apr 30, 2023 at 10:35:29AM +0100, Pavel Begunkov wrote: > > There are several problems with splice requests, aka IORING_OP_SPLICE: > > 1) They are always executed by a worker thread, which is a slow path, > > as we don't have any reliable way to execute it NOWAIT. > > 2) It can't easily poll for data, as there are 2 files it operates on. > > It would either need to track what file to poll or poll both of them, > > in both cases it'll be a mess and add lot of overhead. > > 3) It has to have pipes in the middle, which adds overhead and is not > > great from the uapi design perspective when it goes for io_uring > > requests. > > 4) We want to operate with spliced data as with a normal buffer, i.e. > > write / send / etc. data as normally while it's zerocopy. > > > > It can partially be solved, but the root cause is a suboptimal for > > io_uring design of IORING_OP_SPLICE. Introduce a new request type > > called IORING_OP_GET_BUF, inspired by splice(2) as well as other > > proposals like fused requests. The main idea is to use io_uring's > > registered buffers as the middle man instead of pipes. Once a buffer > > is fetched / spliced from a file using a new fops callback > > ->iou_get_buf, it's installed as a registered buffers and can be used > > by all operations supporting the feature. > > > > Once the userspace releases the buffer, io_uring will wait for all > > requests using the buffer to complete and then use a file provided > > callback ->release() to return the buffer back. It operates on the > > In the commit of "io_uring: add an example for buf-get op", I don't see > any code to release the buffer, can you explain it in details about how > to release the buffer in userspace? And add it in your example? > > Here I guess the ->release() is called in the following code path: > > io_buffer_unmap > io_rsrc_buf_put > io_rsrc_put_work > io_rsrc_node_ref_zero > io_put_rsrc_node > > If it is true, what is counter-pair code for io_put_rsrc_node()? It is io_req_set_rsrc_node() called from io_prep_rw() and io_send_zc_prep(). So only fs IO and net zc supports it, however the fixed buffer is used in ->prep(), that means this way can't work when the rw/net_send_zc OP follows IORING_OP_GET_BUF by IO_LINK. This way is one big defect because IOSQE_IO_LINK does simplify application a lot. Thanks, Ming
