linux-kernel - Re: [PATCH v5 07/11] iov_iter: Add a kernel-type iterator-only iteration function

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Message-ID: <20230922093401.GW224399@kernel.org>
Date:   Fri, 22 Sep 2023 10:34:01 +0100
From:   Simon Horman <horms@...nel.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Christian Brauner <christian@...uner.io>,
        David Laight <David.Laight@...lab.com>,
        Matthew Wilcox <willy@...radead.org>,
        Jeff Layton <jlayton@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-mm@...ck.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 07/11] iov_iter: Add a kernel-type iterator-only
 iteration function

On Wed, Sep 20, 2023 at 11:22:27PM +0100, David Howells wrote:
> Add an iteration function that can only iterate over kernel internal-type
> iterators (ie. BVEC, KVEC, XARRAY) and not user-backed iterators (ie. UBUF
> and IOVEC).  This allows for smaller iterators to be built when it is known
> the caller won't have a user-backed iterator.
> 
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Alexander Viro <viro@...iv.linux.org.uk>
> cc: Jens Axboe <axboe@...nel.dk>
> cc: Christoph Hellwig <hch@....de>
> cc: Christian Brauner <christian@...uner.io>
> cc: Matthew Wilcox <willy@...radead.org>
> cc: Linus Torvalds <torvalds@...ux-foundation.org>
> cc: David Laight <David.Laight@...LAB.COM>
> cc: linux-block@...r.kernel.org
> cc: linux-fsdevel@...r.kernel.org
> cc: linux-mm@...ck.org
> ---
>  include/linux/iov_iter.h | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/include/linux/iov_iter.h b/include/linux/iov_iter.h
> index 270454a6703d..a94d605d7386 100644
> --- a/include/linux/iov_iter.h
> +++ b/include/linux/iov_iter.h
> @@ -271,4 +271,35 @@ size_t iterate_and_advance(struct iov_iter *iter, size_t len, void *priv,
>  	return iterate_and_advance2(iter, len, priv, NULL, ustep, step);
>  }
>  
> +/**
> + * iterate_and_advance_kernel - Iterate over a kernel iterator
> + * @iter: The iterator to iterate over.
> + * @len: The amount to iterate over.
> + * @priv: Data for the step functions.

nit: an entry for @priv2 belongs here

> + * @step: Processing function; given kernel addresses.
> + *
> + * Like iterate_and_advance2(), but rejected UBUF and IOVEC iterators and does
> + * not take a user-step function.
> + */
> +static __always_inline
> +size_t iterate_and_advance_kernel(struct iov_iter *iter, size_t len, void *priv,
> +				  void *priv2, iov_step_f step)
> +{

...