ITER_XARRAY get_pages fix; now the return value is a lot saner

(and more similar to logics for other flavours)
 
 Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Merge tag 'pull-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull iov_iter fix from Al Viro:
 "ITER_XARRAY get_pages fix; now the return value is a lot saner (and
  more similar to logics for other flavours)"

* tag 'pull-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  iov_iter: Fix iter_xarray_get_pages{,_alloc}()

lib/iov_iter.c

@@ -1434,7 +1434,7 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i,
 {
 	unsigned nr, offset;
 	pgoff_t index, count;
-	size_t size = maxsize, actual;
+	size_t size = maxsize;
 	loff_t pos;
 
 	if (!size || !maxpages)
@@ -1461,13 +1461,7 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i,
 	if (nr == 0)
 		return 0;
 
-	actual = PAGE_SIZE * nr;
-	actual -= offset;
-	if (nr == count && size > 0) {
-		unsigned last_offset = (nr > 1) ? 0 : offset;
-		actual -= PAGE_SIZE - (last_offset + size);
-	}
-	return actual;
+	return min(nr * PAGE_SIZE - offset, maxsize);
 }
 
 /* must be done on non-empty ITER_IOVEC one */
@@ -1602,7 +1596,7 @@ static ssize_t iter_xarray_get_pages_alloc(struct iov_iter *i,
 	struct page **p;
 	unsigned nr, offset;
 	pgoff_t index, count;
-	size_t size = maxsize, actual;
+	size_t size = maxsize;
 	loff_t pos;
 
 	if (!size)
@@ -1631,13 +1625,7 @@ static ssize_t iter_xarray_get_pages_alloc(struct iov_iter *i,
 	if (nr == 0)
 		return 0;
 
-	actual = PAGE_SIZE * nr;
-	actual -= offset;
-	if (nr == count && size > 0) {
-		unsigned last_offset = (nr > 1) ? 0 : offset;
-		actual -= PAGE_SIZE - (last_offset + size);
-	}
-	return actual;
+	return min(nr * PAGE_SIZE - offset, maxsize);
 }
 
 ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,