On 11/12/24 2:01 PM, Jens Axboe wrote:
> This is why io_kiocb->async_data exists. uring_cmd is already using that
> for the sqe, I think you'd want to add a 2nd "void *op_data" or
> something in there, and have the uring_cmd alloc cache get clear that to
> NULL and have uring_cmd alloc cache put kfree() it if it's non-NULL.
> 
> We'd also need to move the uring_cache struct into
> include/linux/io_uring_types.h so that btrfs can get to it (and probably
> rename it to something saner, uring_cmd_async_data for example).

Here are two patches that implement that basic thing on the io_uring
uring_cmd side. With that, you can then do:

> static int btrfs_uring_encoded_write(struct io_uring_cmd *cmd, unsigned int issue_flags)
> {
> 	struct io_kiocb *req = cmd_to_io_kiocb(cmd);
> 	struct uring_cmd_async_data *data = req->async_data;
> 	struct btrfs_ioctl_encoded_io_args *args;
> 
> 	if (!data->op_data) {
> 		data->op_data = kmalloc(sizeof(*args), GFP_NOIO);
> 		if (!data->op_data)
> 			return -ENOMEM;
> 		if (copy_from_user(data->op_data, sqe_addr, sizeof(*args))
> 			return -EFAULT;
> 	}
> 	...
> }

and have it be both stable, and not need to worry about freeing it
either. Hope that helps. Totally untested...

-- 
Jens Axboe