[PATCH 1/4] iov_iter: add copy_to_iter_full()

[Jens Axboe <axboe@kernel.dk>]

Add variant of copy_to_iter() that either copies the full amount asked
for and return success, or ensures that the iov_iter is back to where
it started on failure and returns false.

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 include/linux/uio.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 00cebe2b70de..9e9510672b28 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -197,6 +197,16 @@ size_t copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 	return 0;
 }
 
+static __always_inline __must_check
+bool copy_to_iter_full(const void *addr, size_t bytes, struct iov_iter *i)
+{
+	size_t copied = copy_to_iter(addr, bytes, i);
+	if (likely(copied == bytes))
+		return true;
+	iov_iter_revert(i, copied);
+	return false;
+}
+
 static __always_inline __must_check
 size_t copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
 {
-- 
2.43.0