1 files changed, 13 insertions, 1 deletions

diff --git a/include/linux/uio.h b/include/linux/uio.h
index e2231e47cec1..d54985e0705e 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -94,8 +94,20 @@ static inline size_t iov_iter_count(struct iov_iter *i)
         return i->count;
 }
 
-static inline void iov_iter_truncate(struct iov_iter *i, size_t count)
+/*
+ * Cap the iov_iter by given limit; note that the second argument is
+ * *not* the new size - it's upper limit for such.  Passing it a value
+ * greater than the amount of data in iov_iter is fine - it'll just do
+ * nothing in that case.
+ */
+static inline void iov_iter_truncate(struct iov_iter *i, u64 count)
 {
+        /*
+         * count doesn't have to fit in size_t - comparison extends both
+         * operands to u64 here and any value that would be truncated by
+         * conversion in assignement is by definition greater than all
+         * values of size_t, including old i->count.
+         */
         if (i->count > count)
                 i->count = count;
 }