Add an internal struct iovec that we can return as a pointer, with the
fields of the iovec overlapping with the ITER_UBUF ubuf and length
fields.
Then we can have iter_iov() check for the appropriate type, and return
&iter->__ubuf_iovec for ITER_UBUF and iter->__iov for ITER_IOVEC and
things will magically work out for a single segment request regardless
of either type.
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
include/linux/uio.h | 44 +++++++++++++++++++++++++++++++++++---------
1 file changed, 35 insertions(+), 9 deletions(-)
diff --git a/include/linux/uio.h b/include/linux/uio.h
index 5dbd2dcab35c..ed35f4427a0a 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -49,15 +49,35 @@ struct iov_iter {
size_t iov_offset;
int last_offset;
};
- size_t count;
+ /*
+ * Hack alert: overlay ubuf_iovec with iovec + count, so
+ * that the members resolve correctly regardless of the type
+ * of iterator used. This means that you can use:
+ *
+ * &iter->__ubuf_iovec or iter->__iov
+ *
+ * interchangably for the user_backed cases, hence simplifying
+ * some of the cases that need to deal with both.
+ */
union {
- /* use iter_iov() to get the current vec */
- const struct iovec *__iov;
- const struct kvec *kvec;
- const struct bio_vec *bvec;
- struct xarray *xarray;
- struct pipe_inode_info *pipe;
- void __user *ubuf;
+ /*
+ * This really should be a const, but we cannot do that without
+ * also modifying any of the zero-filling iter init functions.
+ * Leave it non-const for now, but it should be treated as such.
+ */
+ struct iovec __ubuf_iovec;
+ struct {
+ union {
+ /* use iter_iov() to get the current vec */
+ const struct iovec *__iov;
+ const struct kvec *kvec;
+ const struct bio_vec *bvec;
+ struct xarray *xarray;
+ struct pipe_inode_info *pipe;
+ void __user *ubuf;
+ };
+ size_t count;
+ };
};
union {
unsigned long nr_segs;
@@ -69,7 +89,13 @@ struct iov_iter {
};
};
-#define iter_iov(iter) (iter)->__iov
+static inline const struct iovec *iter_iov(const struct iov_iter *iter)
+{
+ if (iter->iter_type == ITER_UBUF)
+ return (const struct iovec *) &iter->__ubuf_iovec;
+ return iter->__iov;
+}
+
#define iter_iov_addr(iter) (iter_iov(iter)->iov_base + (iter)->iov_offset)
#define iter_iov_len(iter) (iter_iov(iter)->iov_len - (iter)->iov_offset)
--
2.39.2
