Re: [PATCH 2/6] iov_iter: new iov_iter_pin_pages*(), for FOLL_PIN pages

+ssize_t iov_iter_pin_pages(struct iov_iter *i,
+		   struct page **pages, size_t maxsize, unsigned int maxpages,
+		   size_t *start)
+{
+	size_t len;
+	int n, res;
+
+	if (maxsize > i->count)
+		maxsize = i->count;
+	if (!maxsize)
+		return 0;
+
+	WARN_ON_ONCE(!iter_is_iovec(i));
+
+	if (likely(iter_is_iovec(i))) {
+		unsigned int gup_flags = 0;
+		unsigned long addr;
+
+		if (iov_iter_rw(i) != WRITE)
+			gup_flags |= FOLL_WRITE;
+		if (i->nofault)
+			gup_flags |= FOLL_NOFAULT;
+
+		addr = first_iovec_segment(i, &len, start, maxsize, maxpages);
+		n = DIV_ROUND_UP(len, PAGE_SIZE);
+		res = pin_user_pages_fast(addr, n, gup_flags, pages);
+		if (unlikely(res <= 0))
+			return res;
+		return (res == n ? len : res * PAGE_SIZE) - *start;

Trying to be clever like that just makes the code a lot less readable. I
should not have to reason about a return value. Same in the other
function.

-- 
Jens Axboe