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Date: Fri, 22 Sep 2023 10:34:01 +0100
From: Simon Horman <horms@kernel.org>
To: David Howells <dhowells@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>, Al Viro <viro@zeniv.linux.org.uk>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Christoph Hellwig <hch@lst.de>,
	Christian Brauner <christian@brauner.io>,
	David Laight <David.Laight@aculab.com>,
	Matthew Wilcox <willy@infradead.org>,
	Jeff Layton <jlayton@kernel.org>, linux-fsdevel@vger.kernel.org,
	linux-block@vger.kernel.org, linux-mm@kvack.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 07/11] iov_iter: Add a kernel-type iterator-only
 iteration function
Message-ID: <20230922093401.GW224399@kernel.org>
References: <20230920222231.686275-1-dhowells@redhat.com>
 <20230920222231.686275-8-dhowells@redhat.com>
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In-Reply-To: <20230920222231.686275-8-dhowells@redhat.com>

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@redhat.com>
> cc: Alexander Viro <viro@zeniv.linux.org.uk>
> cc: Jens Axboe <axboe@kernel.dk>
> cc: Christoph Hellwig <hch@lst.de>
> cc: Christian Brauner <christian@brauner.io>
> cc: Matthew Wilcox <willy@infradead.org>
> cc: Linus Torvalds <torvalds@linux-foundation.org>
> cc: David Laight <David.Laight@ACULAB.COM>
> cc: linux-block@vger.kernel.org
> cc: linux-fsdevel@vger.kernel.org
> cc: linux-mm@kvack.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)
> +{

...