linux-kernel - Re: [PATCH v2 10/12] [xen] fix "direction" argument of iov_iter

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Date:   Fri, 28 Oct 2022 08:48:22 -0400
From:   John Stoffel <john@...d.stoffel.home>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Christoph Hellwig <hch@...radead.org>,
        David Howells <dhowells@...hat.com>, willy@...radead.org,
        dchinner@...hat.com, Steve French <smfrench@...il.com>,
        Shyam Prasad N <nspmangalore@...il.com>,
        Rohith Surabattula <rohiths.msft@...il.com>,
        Jeff Layton <jlayton@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>, torvalds@...ux-foundation.org,
        linux-cifs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 10/12] [xen] fix "direction" argument of
 iov_iter_kvec()

On Fri, Oct 28, 2022 at 03:33:50AM +0100, Al Viro wrote:
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> ---
>  drivers/xen/pvcalls-back.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c
> index d6f945fd4147..21b9c850a382 100644
> --- a/drivers/xen/pvcalls-back.c
> +++ b/drivers/xen/pvcalls-back.c
> @@ -129,13 +129,13 @@ static bool pvcalls_conn_back_read(void *opaque)
>  	if (masked_prod < masked_cons) {
>  		vec[0].iov_base = data->in + masked_prod;
>  		vec[0].iov_len = wanted;
> -		iov_iter_kvec(&msg.msg_iter, WRITE, vec, 1, wanted);
> +		iov_iter_kvec(&msg.msg_iter, READ, vec, 1, wanted);


Wouldn't it make more sense to use READER and WRITER here, since the
current READ/WRITE are 100% non-obvious?  This is probably a bigger
change, but this just looks wrong and will be so easy for people to
screw up again and again down the line.


>  	} else {
>  		vec[0].iov_base = data->in + masked_prod;
>  		vec[0].iov_len = array_size - masked_prod;
>  		vec[1].iov_base = data->in;
>  		vec[1].iov_len = wanted - vec[0].iov_len;
> -		iov_iter_kvec(&msg.msg_iter, WRITE, vec, 2, wanted);
> +		iov_iter_kvec(&msg.msg_iter, READ, vec, 2, wanted);
>  	}
>  
>  	atomic_set(&map->read, 0);
> @@ -188,13 +188,13 @@ static bool pvcalls_conn_back_write(struct sock_mapping *map)
>  	if (pvcalls_mask(prod, array_size) > pvcalls_mask(cons, array_size)) {
>  		vec[0].iov_base = data->out + pvcalls_mask(cons, array_size);
>  		vec[0].iov_len = size;
> -		iov_iter_kvec(&msg.msg_iter, READ, vec, 1, size);
> +		iov_iter_kvec(&msg.msg_iter, WRITE, vec, 1, size);
>  	} else {
>  		vec[0].iov_base = data->out + pvcalls_mask(cons, array_size);
>  		vec[0].iov_len = array_size - pvcalls_mask(cons, array_size);
>  		vec[1].iov_base = data->out;
>  		vec[1].iov_len = size - vec[0].iov_len;
> -		iov_iter_kvec(&msg.msg_iter, READ, vec, 2, size);
> +		iov_iter_kvec(&msg.msg_iter, WRITE, vec, 2, size);
>  	}
>  
>  	atomic_set(&map->write, 0);
> -- 
> 2.30.2
> 

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