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

[Sidong Yang <sidong.yang@furiosa.ai>]

On Thu, Mar 20, 2025 at 12:01:42PM +0000, Pavel Begunkov wrote:
> 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?

I think it's okay to leave the old version as it is. Making it to refuse
the flag could break user application.

Thanks,
Sidong

> 
> Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
> 
> > 
> > Signed-off-by: Sidong Yang <sidong.yang@furiosa.ai>
> > ---
> >   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
>