From 79cfe9e59c2a12c3b3faeeefe38d23f3d8030972 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Mon, 21 Oct 2024 13:34:10 -0600 Subject: io_uring/register: add IORING_REGISTER_RESIZE_RINGS Once a ring has been created, the size of the CQ and SQ rings are fixed. Usually this isn't a problem on the SQ ring side, as it merely controls the available number of requests that can be submitted in a single system call, and there's rarely a need to change that. For the CQ ring, it's a different story. For most efficient use of io_uring, it's important that the CQ ring never overflows. This means that applications must size it for the worst case scenario, which can be wasteful. Add IORING_REGISTER_RESIZE_RINGS, which allows an application to resize the existing rings. It takes a struct io_uring_params argument, the same one which is used to setup the ring initially, and resizes rings according to the sizes given. Certain properties are always inherited from the original ring setup, like SQE128/CQE32 and other setup options. The implementation only allows flag associated with how the CQ ring is sized and clamped. Existing unconsumed SQE and CQE entries are copied as part of the process. If either the SQ or CQ resized destination ring cannot hold the entries already present in the source rings, then the operation is failed with -EOVERFLOW. Any register op holds ->uring_lock, which prevents new submissions, and the internal mapping holds the completion lock as well across moving CQ ring state. To prevent races between mmap and ring resizing, add a mutex that's solely used to serialize ring resize and mmap. mmap_sem can't be used here, as as fork'ed process may be doing mmaps on the ring as well. The ctx->resize_lock is held across mmap operations, and the resize will grab it before swapping out the already mapped new data. Signed-off-by: Jens Axboe --- include/uapi/linux/io_uring.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include/uapi/linux/io_uring.h') diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h index 86cb385fe0b5..60b9c98595fa 100644 --- a/include/uapi/linux/io_uring.h +++ b/include/uapi/linux/io_uring.h @@ -615,6 +615,11 @@ enum io_uring_register_op { /* send MSG_RING without having a ring */ IORING_REGISTER_SEND_MSG_RING = 31, + /* 32 reserved for zc rx */ + + /* resize CQ ring */ + IORING_REGISTER_RESIZE_RINGS = 33, + /* this goes last */ IORING_REGISTER_LAST, -- cgit v1.2.3