Re: [PATCH 03/25] ALSA: core: Add memory copy helpers between iov_iter and iomem

On Mon, Aug 14, 2023 at 01:55:01PM +0200, Takashi Iwai wrote:

Add two more helpers for copying memory between iov_iter and iomem, which will be used by the new PCM copy ops in a few drivers. The existing helpers became wrappers of those now.

Note that copy_from/to_iter() returns the copied bytes, hence the error condition is inverted from copy_from/to_user().

...

• return copy_to_user(dst, (const void __force*)src, count) ? -EFAULT : 0;

• return !copy_to_iter((const void __force *)src, count, dst) ? -EFAULT : 0;

Inverted means, I believe, this

return copy_to_iter((const void __force *)src, count, dst) == count ? 0 : -EFAULT;

as far as I understand the idea behind the copy_to_user() return value.

Ditto for other cases.