Re: [PATCH v2 02/10] iov: Add iov_memcpy() to copy data between iovec arrays

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

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On Fri, Apr 03, 2026 at 06:38:03PM +0200, Laurent Vivier wrote:
> Add a helper to copy data from a source iovec array to a destination
> iovec array, each starting at an arbitrary byte offset, iterating
> through both arrays simultaneously and copying in chunks matching the
> smaller of the two current segments.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  iov.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  iov.h |  3 +++
>  2 files changed, 55 insertions(+)
> 
> diff --git a/iov.c b/iov.c
> index 0188acdf5eba..dabc4f1ceea3 100644
> --- a/iov.c
> +++ b/iov.c
> @@ -197,6 +197,58 @@ void iov_memset(const struct iovec *iov, size_t iov_cnt, size_t offset, int c,
>  	}
>  }
>  
> +/**
> + * iov_memcpy() - Copy data between two iovec arrays
> + * @dst_iov:		Destination iovec array
> + * @dst_iov_cnt:	Number of elements in destination iovec array
> + * @dst_offset:		Destination offset
> + * @src_iov:		Source iovec array
> + * @src_iov_cnt:	Number of elements in source iovec array
> + * @offs:		Source offset
> + * @length:		Number of bytes to copy
> + *
> + * Return: total number of bytes copied
> + */
> +/* cppcheck-suppress unusedFunction */
> +size_t iov_memcpy(struct iovec *dst_iov, size_t dst_iov_cnt, size_t dst_offset,
> +		  const struct iovec *src_iov, size_t src_iov_cnt,
> +		  size_t src_offset, size_t length)
> +{
> +	unsigned int i, j;
> +	size_t total = 0;
> +
> +	i = iov_skip_bytes(src_iov, src_iov_cnt, src_offset, &src_offset);
> +	j = iov_skip_bytes(dst_iov, dst_iov_cnt, dst_offset, &dst_offset);
> +
> +	/* copying data */
> +	while (length && i < src_iov_cnt && j < dst_iov_cnt) {
> +		size_t n = MIN(dst_iov[j].iov_len - dst_offset,
> +			       src_iov[i].iov_len - src_offset);
> +
> +		if (n > length)
> +			n = length;
> +
> +		memcpy((char *)dst_iov[j].iov_base + dst_offset,
> +		       (const char *)src_iov[i].iov_base + src_offset, n);
> +
> +		dst_offset += n;
> +		src_offset += n;
> +		total += n;
> +		length -= n;
> +
> +		if (dst_offset == dst_iov[j].iov_len) {
> +			dst_offset = 0;
> +			j++;
> +		}
> +		if (src_offset == src_iov[i].iov_len) {
> +			src_offset = 0;
> +			i++;
> +		}
> +	}
> +
> +	return total;
> +}
> +
>  /**
>   * iov_tail_prune() - Remove any unneeded buffers from an IOV tail
>   * @tail:	IO vector tail (modified)
> diff --git a/iov.h b/iov.h
> index d295d05b3bab..3c63308e554f 100644
> --- a/iov.h
> +++ b/iov.h
> @@ -32,6 +32,9 @@ size_t iov_size(const struct iovec *iov, size_t iov_cnt);
>  size_t iov_truncate(struct iovec *iov, size_t iov_cnt, size_t size);
>  void iov_memset(const struct iovec *iov, size_t iov_cnt, size_t offset, int c,
>  		size_t length);
> +size_t iov_memcpy(struct iovec *dst_iov, size_t dst_iov_cnt, size_t dst_offset,
> +		  const struct iovec *src_iov, size_t src_iov_cnt,
> +		  size_t src_offset, size_t length);
>  
>  /*
>   * DOC: Theory of Operation, struct iov_tail
> -- 
> 2.53.0
> 

-- 
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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