Re: [RFC PATCH v5 5/5] btrfs: ioctl: introduce btrfs_uring_import_iovec()

[Pavel Begunkov <asml.silence@xxxxxxxxx>]

On 3/19/25 06:12, Sidong Yang wrote:
> This patch introduces btrfs_uring_import_iovec(). In encoded read/write
> with uring cmd, it uses import_iovec without supporting fixed buffer.
> btrfs_using_import_iovec() could use fixed buffer if cmd flags has
> IORING_URING_CMD_FIXED.

Looks fine to me. The only comment, it appears btrfs silently ignored
IORING_URING_CMD_FIXED before, so theoretically it changes the uapi.
It should be fine, but maybe we should sneak in and backport a patch
refusing the flag for older kernels?

Reviewed-by: Pavel Begunkov <asml.silence@xxxxxxxxx>

> Signed-off-by: Sidong Yang <sidong.yang@xxxxxxxxxx>
> ---
>   fs/btrfs/ioctl.c | 34 +++++++++++++++++++++++++---------
>   1 file changed, 25 insertions(+), 9 deletions(-)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 6c18bad53cd3..e5b4af41ca6b 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -4802,7 +4802,29 @@ struct btrfs_uring_encoded_data {
>   	struct iov_iter iter;
>   };
>   
> -static int btrfs_uring_encoded_read(struct io_uring_cmd *cmd, unsigned int issue_flags)
> +static int btrfs_uring_import_iovec(struct io_uring_cmd *cmd,
> +				    unsigned int issue_flags, int rw)
> +{
> +	struct btrfs_uring_encoded_data *data =
> +		io_uring_cmd_get_async_data(cmd)->op_data;
> +	int ret;
> +
> +	if (cmd->flags & IORING_URING_CMD_FIXED) {
> +		data->iov = NULL;
> +		ret = io_uring_cmd_import_fixed_vec(cmd, data->args.iov,
> +						    data->args.iovcnt, rw,
> +						    &data->iter, issue_flags);
> +	} else {
> +		data->iov = data->iovstack;
> +		ret = import_iovec(rw, data->args.iov, data->args.iovcnt,
> +				   ARRAY_SIZE(data->iovstack), &data->iov,
> +				   &data->iter);
> +	}
> +	return ret;
> +}
> +
> +static int btrfs_uring_encoded_read(struct io_uring_cmd *cmd,
> +				    unsigned int issue_flags)
>   {
>   	size_t copy_end_kernel = offsetofend(struct btrfs_ioctl_encoded_io_args, flags);
>   	size_t copy_end;
> @@ -4874,10 +4896,7 @@ static int btrfs_uring_encoded_read(struct io_uring_cmd *cmd, unsigned int issue
>   			goto out_acct;
>   		}
>   
> -		data->iov = data->iovstack;
> -		ret = import_iovec(ITER_DEST, data->args.iov, data->args.iovcnt,
> -				   ARRAY_SIZE(data->iovstack), &data->iov,
> -				   &data->iter);
> +		ret = btrfs_uring_import_iovec(cmd, issue_flags, ITER_DEST);
>   		if (ret < 0)
>   			goto out_acct;
>   
> @@ -5022,10 +5041,7 @@ static int btrfs_uring_encoded_write(struct io_uring_cmd *cmd, unsigned int issu
>   		if (data->args.len > data->args.unencoded_len - data->args.unencoded_offset)
>   			goto out_acct;
>   
> -		data->iov = data->iovstack;
> -		ret = import_iovec(ITER_SOURCE, data->args.iov, data->args.iovcnt,
> -				   ARRAY_SIZE(data->iovstack), &data->iov,
> -				   &data->iter);
> +		ret = btrfs_uring_import_iovec(cmd, issue_flags, ITER_SOURCE);
>   		if (ret < 0)
>   			goto out_acct;
>   

--
Pavel Begunkov