From fc68fcda049108478ee4704d8a3ad3e05cc72fd0 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Mon, 11 Sep 2023 13:35:42 -0600
Subject: [PATCH] io_uring/rw: add support for IORING_OP_READ_MULTISHOT
This behaves like IORING_OP_READ, except:
1) It only supports pollable files (eg pipes, sockets, etc). Note that
for sockets, you probably want to use recv/recvmsg with multishot
instead.
2) It supports multishot mode, meaning it will repeatedly trigger a
read and fill a buffer when data is available. This allows similar
use to recv/recvmsg but on non-sockets, where a single request will
repeatedly post a CQE whenever data is read from it.
3) Because of #2, it must be used with provided buffers. This is
uniformly true across any request type that supports multishot and
transfers data, with the reason being that it's obviously not
possible to pass in a single buffer for the data, as multiple reads
may very well trigger before an application has a chance to process
previous CQEs and the data passed from them.
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
include/uapi/linux/io_uring.h | 1 +
io_uring/opdef.c | 13 ++++++-
io_uring/rw.c | 67 +++++++++++++++++++++++++++++++++++
io_uring/rw.h | 2 ++
4 files changed, 82 insertions(+), 1 deletion(-)
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 8e61f8b7c2ced..d127948b0d8a8 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -240,6 +240,7 @@ enum io_uring_op {
IORING_OP_URING_CMD,
IORING_OP_SEND_ZC,
IORING_OP_SENDMSG_ZC,
+ IORING_OP_READ_MULTISHOT,
/* this goes last, obviously */
IORING_OP_LAST,
diff --git a/io_uring/opdef.c b/io_uring/opdef.c
index f409040655007..a3fb1f9b3998e 100644
--- a/io_uring/opdef.c
+++ b/io_uring/opdef.c
@@ -430,9 +430,17 @@ const struct io_issue_def io_issue_defs[] = {
.prep = io_eopnotsupp_prep,
#endif
},
+ [IORING_OP_READ_MULTISHOT] = {
+ .needs_file = 1,
+ .unbound_nonreg_file = 1,
+ .pollin = 1,
+ .buffer_select = 1,
+ .audit_skip = 1,
+ .prep = io_read_mshot_prep,
+ .issue = io_read_mshot,
+ },
};
-
const struct io_cold_def io_cold_defs[] = {
[IORING_OP_NOP] = {
.name = "NOP",
@@ -650,6 +658,9 @@ const struct io_cold_def io_cold_defs[] = {
.fail = io_sendrecv_fail,
#endif
},
+ [IORING_OP_READ_MULTISHOT] = {
+ .name = "READ_MULTISHOT",
+ },
};
const char *io_uring_get_opcode(u8 opcode)
diff --git a/io_uring/rw.c b/io_uring/rw.c
index 83ae911c2868c..ec0cc38ea6824 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -123,6 +123,22 @@ int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe)
return 0;
}
+/*
+ * Multishot read is prepared just like a normal read/write request, only
+ * difference is that we set the MULTISHOT flag.
+ */
+int io_read_mshot_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+ int ret;
+
+ ret = io_prep_rw(req, sqe);
+ if (unlikely(ret))
+ return ret;
+
+ req->flags |= REQ_F_APOLL_MULTISHOT;
+ return 0;
+}
+
void io_readv_writev_cleanup(struct io_kiocb *req)
{
struct io_async_rw *io = req->async_data;
@@ -869,6 +885,57 @@ int io_read(struct io_kiocb *req, unsigned int issue_flags)
return ret;
}
+int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags)
+{
+ unsigned int cflags = 0;
+ int ret;
+
+ /*
+ * Multishot MUST be used on a pollable file
+ */
+ if (!file_can_poll(req->file))
+ return -EBADFD;
+
+ ret = __io_read(req, issue_flags);
+
+ /*
+ * If we get -EAGAIN, recycle our buffer and just let normal poll
+ * handling arm it.
+ */
+ if (ret == -EAGAIN) {
+ io_kbuf_recycle(req, issue_flags);
+ return -EAGAIN;
+ }
+
+ /*
+ * Any successful return value will keep the multishot read armed.
+ */
+ if (ret > 0) {
+ /*
+ * Put our buffer and post a CQE. If we fail to post a CQE, then
+ * jump to the termination path. This request is then done.
+ */
+ cflags = io_put_kbuf(req, issue_flags);
+
+ if (io_fill_cqe_req_aux(req,
+ issue_flags & IO_URING_F_COMPLETE_DEFER,
+ ret, cflags | IORING_CQE_F_MORE)) {
+ if (issue_flags & IO_URING_F_MULTISHOT)
+ return IOU_ISSUE_SKIP_COMPLETE;
+ return -EAGAIN;
+ }
+ }
+
+ /*
+ * Either an error, or we've hit overflow posting the CQE. For any
+ * multishot request, hitting overflow will terminate it.
+ */
+ io_req_set_res(req, ret, cflags);
+ if (issue_flags & IO_URING_F_MULTISHOT)
+ return IOU_STOP_MULTISHOT;
+ return IOU_OK;
+}
+
int io_write(struct io_kiocb *req, unsigned int issue_flags)
{
struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
diff --git a/io_uring/rw.h b/io_uring/rw.h
index 4b89f9659366a..c5aed03d42a4d 100644
--- a/io_uring/rw.h
+++ b/io_uring/rw.h
@@ -23,3 +23,5 @@ int io_writev_prep_async(struct io_kiocb *req);
void io_readv_writev_cleanup(struct io_kiocb *req);
void io_rw_fail(struct io_kiocb *req);
void io_req_rw_complete(struct io_kiocb *req, struct io_tw_state *ts);
+int io_read_mshot_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags);
--
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