Normally MSG_RING requires both a source and a destination ring. But
some users don't always have a ring avilable to send a message from, yet
they still need to notify a target ring.
Add support for using io_uring_register(2) without having a source ring,
using a file descriptor of -1 for that. Internally those are called
blind registration opcodes. Implement IORING_REGISTER_SEND_MSG_RING as a
blind opcode, which simply takes an sqe that the application can put on
the stack and use the normal liburing helpers to initialize it. Then the
app can call:
io_uring_register(-1, IORING_REGISTER_SEND_MSG_RING, &sqe, 1);
and get the same behavior in terms of the target, where a CQE is posted
with the details given in the sqe.
For now this takes a single sqe pointer argument, and hence arg must
be set to that, and nr_args must be 1. Could easily be extended to take
an array of sqes, but for now let's keep it simple.
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
include/uapi/linux/io_uring.h | 3 +++
io_uring/msg_ring.c | 29 +++++++++++++++++++++++++++++
io_uring/msg_ring.h | 1 +
io_uring/register.c | 30 ++++++++++++++++++++++++++++++
4 files changed, 63 insertions(+)
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 1fe79e750470..86cb385fe0b5 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -612,6 +612,9 @@ enum io_uring_register_op {
/* clone registered buffers from source ring to current ring */
IORING_REGISTER_CLONE_BUFFERS = 30,
+ /* send MSG_RING without having a ring */
+ IORING_REGISTER_SEND_MSG_RING = 31,
+
/* this goes last */
IORING_REGISTER_LAST,
diff --git a/io_uring/msg_ring.c b/io_uring/msg_ring.c
index b8c527f08cd5..edea1ffd501c 100644
--- a/io_uring/msg_ring.c
+++ b/io_uring/msg_ring.c
@@ -331,6 +331,35 @@ int io_msg_ring(struct io_kiocb *req, unsigned int issue_flags)
return IOU_OK;
}
+int io_uring_sync_msg_ring(struct io_uring_sqe *sqe)
+{
+ struct io_msg io_msg = { };
+ struct fd f;
+ int ret;
+
+ ret = __io_msg_ring_prep(&io_msg, sqe);
+ if (unlikely(ret))
+ return ret;
+
+ /*
+ * Only data sending supported, not IORING_MSG_SEND_FD as that one
+ * doesn't make sense without a source ring to send files from.
+ */
+ if (io_msg.cmd != IORING_MSG_DATA)
+ return -EINVAL;
+
+ ret = -EBADF;
+ f = fdget(sqe->fd);
+ if (fd_file(f)) {
+ ret = -EBADFD;
+ if (io_is_uring_fops(fd_file(f)))
+ ret = __io_msg_ring_data(fd_file(f)->private_data,
+ &io_msg, IO_URING_F_UNLOCKED);
+ fdput(f);
+ }
+ return ret;
+}
+
void io_msg_cache_free(const void *entry)
{
struct io_kiocb *req = (struct io_kiocb *) entry;
diff --git a/io_uring/msg_ring.h b/io_uring/msg_ring.h
index 3030f3942f0f..38e7f8f0c944 100644
--- a/io_uring/msg_ring.h
+++ b/io_uring/msg_ring.h
@@ -1,5 +1,6 @@
// SPDX-License-Identifier: GPL-2.0
+int io_uring_sync_msg_ring(struct io_uring_sqe *sqe);
int io_msg_ring_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
int io_msg_ring(struct io_kiocb *req, unsigned int issue_flags);
void io_msg_ring_cleanup(struct io_kiocb *req);
diff --git a/io_uring/register.c b/io_uring/register.c
index eca26d4884d9..52b2f9b74af8 100644
--- a/io_uring/register.c
+++ b/io_uring/register.c
@@ -28,6 +28,7 @@
#include "kbuf.h"
#include "napi.h"
#include "eventfd.h"
+#include "msg_ring.h"
#define IORING_MAX_RESTRICTIONS (IORING_RESTRICTION_LAST + \
IORING_REGISTER_LAST + IORING_OP_LAST)
@@ -588,6 +589,32 @@ struct file *io_uring_register_get_file(unsigned int fd, bool registered)
return ERR_PTR(-EOPNOTSUPP);
}
+/*
+ * "blind" registration opcodes are ones where there's no ring given, and
+ * hence the source fd must be -1.
+ */
+static int io_uring_register_blind(unsigned int opcode, void __user *arg,
+ unsigned int nr_args)
+{
+ switch (opcode) {
+ case IORING_REGISTER_SEND_MSG_RING: {
+ struct io_uring_sqe sqe;
+
+ if (!arg || nr_args != 1)
+ return -EINVAL;
+ if (copy_from_user(&sqe, arg, sizeof(sqe)))
+ return -EFAULT;
+ /* no flags supported */
+ if (sqe.flags)
+ return -EINVAL;
+ if (sqe.opcode == IORING_OP_MSG_RING)
+ return io_uring_sync_msg_ring(&sqe);
+ }
+ }
+
+ return -EINVAL;
+}
+
SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
void __user *, arg, unsigned int, nr_args)
{
@@ -602,6 +629,9 @@ SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
if (opcode >= IORING_REGISTER_LAST)
return -EINVAL;
+ if (fd == -1)
+ return io_uring_register_blind(opcode, arg, nr_args);
+
file = io_uring_register_get_file(fd, use_registered_ring);
if (IS_ERR(file))
return PTR_ERR(file);
--
2.45.2
