Subject: Re: [PATCH v3 net-next 01/21] iov_iter: Introduce new procedures for copy to iter/pages

From: Christoph Hellwig <[email-masked]>
Date: Mon, 1 Feb 2021 18:35:48 +0100

On Mon, Feb 01, 2021 at 12:04:49PM +0200, Boris Pismenny wrote:
> +static __always_inline __must_check
> +size_t ddp_copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
> +{
> +	if (unlikely(!check_copy_size(addr, bytes, true)))
> +		return 0;
> +	else
> +		return _ddp_copy_to_iter(addr, bytes, i);
> +}

No need for the else after a return, and the normal kernel convention
double underscores for magic internal functions.

But more importantly: does this belong into the generic header without
and comments what the ddp means and when it should be used?

> +static void ddp_memcpy_to_page(struct page *page, size_t offset, const char *from, size_t len)

Overly long line.  But we're also looking into generic helpers for
this kind of things, not sure if they made it to linux-next in the
meantime, but please check.

> +size_t _ddp_copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
> +{
> +	const char *from = addr;
> +	if (unlikely(iov_iter_is_pipe(i)))
> +		return copy_pipe_to_iter(addr, bytes, i);
> +	if (iter_is_iovec(i))
> +		might_fault();
> +	iterate_and_advance(i, bytes, v,
> +		copyout(v.iov_base, (from += v.iov_len) - v.iov_len, v.iov_len),
> +		ddp_memcpy_to_page(v.bv_page, v.bv_offset,
> +				   (from += v.bv_len) - v.bv_len, v.bv_len),
> +		memcpy(v.iov_base, (from += v.iov_len) - v.iov_len, v.iov_len)
> +		)
> +
> +	return bytes;
> +}

This bloats every kernel build, so please move it into a conditionally
built file.  And please document the whole thing.