Re: [PATCH 4/5] iov: add iov_count()

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Jun 21, 2024 at 04:56:39PM +0200, Laurent Vivier wrote:
> Add a function that count how many buffers from a given
> iovec list we need to contain a given number of bytes.
> It also provides how many bytes are used in the last
> buffer if it is not fully filled.

Isn't this equivalent to the iov_skip_bytes() function we already have?

> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  iov.c | 35 +++++++++++++++++++++++++++++++++++
>  iov.h |  2 ++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/iov.c b/iov.c
> index 3741db21790f..793788b5d2bc 100644
> --- a/iov.c
> +++ b/iov.c
> @@ -155,3 +155,38 @@ size_t iov_size(const struct iovec *iov, size_t iov_cnt)
>  
>  	return len;
>  }
> +
> +/**
> + * iov_count - Calculate the number of I/O vectors and the size of
> + *             the last one to store a given number of bytes.
> + *
> + * @iov:       Pointer to the array of struct iovec describing the
> + *             scatter/gather I/O vector.
> + * @iov_cnt:   Number of elements in the iov array.
> + * @size:      number of bytes we need to store in iovec
> + * @last_iov_length: output parameter, length used in the last iovec
> + * 		if return value is 0, this output parameter is
> + * 		undefined.
> + *
> + * Returns:	The number of iovec needed to store @size bytes.
> + */
> +/* cppcheck-suppress unusedFunction */
> +size_t iov_count(const struct iovec *iov, size_t iov_cnt,
> +                 size_t size, size_t *last_iov_length)
> +{
> +	size_t n = 0;
> +
> +	while (size && n < iov_cnt) {
> +		if (size <= iov[n].iov_len) {
> +			*last_iov_length = size;
> +			return n + 1;
> +		}
> +		size -= iov[n].iov_len;
> +		n++;
> +	}
> +
> +	if (n > 0)
> +		*last_iov_length = iov[n - 1].iov_len;
> +
> +	return n;
> +}
> diff --git a/iov.h b/iov.h
> index a9e1722713b3..0fa456d7051b 100644
> --- a/iov.h
> +++ b/iov.h
> @@ -28,4 +28,6 @@ size_t iov_from_buf(const struct iovec *iov, size_t iov_cnt,
>  size_t iov_to_buf(const struct iovec *iov, size_t iov_cnt,
>                    size_t offset, void *buf, size_t bytes);
>  size_t iov_size(const struct iovec *iov, size_t iov_cnt);
> +size_t iov_count(const struct iovec *iov, size_t iov_cnt,
> +		 size_t size, size_t *last_iov_length);
>  #endif /* IOVEC_H */

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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