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io_uring/msg_ring: add support for sending a sync message

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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.

Link: https://lore.kernel.org/r/20240924115932.116167-3-axboe@kernel.dk
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe
2024-09-24 05:57:31 -06:00
parent 95d6c9229a
commit a377132154
4 changed files with 63 additions and 0 deletions
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29
io_uring/msg_ring.c
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@@ -331,6 +331,35 @@ done:
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;