[PATCH 14/14] fs: don't change the address limit for ->read_iter in __kernel_read

[Al Viro]

On Thu, May 28, 2020 at 07:40:43AM +0200, Christoph Hellwig wrote:
> If we read to a file that implements ->read_iter there is no need
> to change the address limit if we send a kvec down.  Implement that
> case, and prefer it over using plain ->read with a changed address
> limit if available.

Ditto re never converting something that bails out on uaccess_kernel()
in ->read() over to ->read_iter().