[PATCH 09/14] fs: don't change the address limit for ->write_iter in __kernel_write

[Al Viro]

On Thu, May 28, 2020 at 07:40:38AM +0200, Christoph Hellwig wrote:
> If we write to a file that implements ->write_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 ->write with a changed address
> limit if available.

Umm...  It needs a comment along the lines of "weird shits like
/dev/sg that currently check for uaccess_kernel() will just
have to make sure they never switch to ->write_iter()"