bio_vec-backed iov_iter

New variant of iov_iter - ITER_BVEC in iter->type, backed with
bio_vec array instead of iovec one.  Primitives taught to deal
with such beasts, __swap_write() switched to using that kind
of iov_iter.

Note that bio_vec is just a <page, offset, length> triple - there's
nothing block-specific about it.  I've left the definition where it
was, but took it from under ifdef CONFIG_BLOCK.

Next target: ->splice_write()...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 12 insertions, 2 deletions

diff --git a/include/linux/uio.h b/include/linux/uio.h
index e8a109a75de1..e2231e47cec1 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -19,12 +19,21 @@ struct kvec {
         size_t iov_len;
 };
 
+enum {
+        ITER_IOVEC = 0,
+        ITER_KVEC = 2,
+        ITER_BVEC = 4,
+};
+
 struct iov_iter {
         int type;
-        const struct iovec *iov;
-        unsigned long nr_segs;
         size_t iov_offset;
         size_t count;
+        union {
+                const struct iovec *iov;
+                const struct bio_vec *bvec;
+        };
+        unsigned long nr_segs;
 };
 
 /*
@@ -54,6 +63,7 @@ static inline struct iovec iov_iter_iovec(const struct iov_iter *iter)
 }
 
 #define iov_for_each(iov, iter, start)                          \
+        if (!((start).type & ITER_BVEC))                        \
         for (iter = (start);                                    \
              (iter).count &&                                    \
              ((iov = iov_iter_iovec(&(iter))), 1);              \