Re: [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable

[Al Viro]

On Fri, Aug 27, 2021 at 06:49:12PM +0200, Andreas Gruenbacher wrote:
> Introduce a new fault_in_iov_iter_writeable helper for safely faulting
> in an iterator for writing.  Uses get_user_pages() to fault in the pages
> without actually writing to them, which would be destructive.
> 
> We'll use fault_in_iov_iter_writeable in gfs2 once we've determined that
> the iterator passed to .read_iter isn't in memory.

Again, the calling conventions are wrong.  Make it success/failure or
0/-EFAULT.  And it's inconsistent for iovec and non-iovec cases as it is.