iov_iter: Separate type from direction and use accessor functions

In the iov_iter struct, separate the iterator type from the iterator
direction and use accessor functions to access them in most places.

Convert a bunch of places to use switch-statements to access them rather
then chains of bitwise-AND statements.  This makes it easier to add further
iterator types.  Also, this can be more efficient as to implement a switch
of small contiguous integers, the compiler can use ~50% fewer compare
instructions than it has to use bitwise-and instructions.

Further, cease passing the iterator type into the iterator setup function.
The iterator function can set that itself.  Only the direction is required.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 15 insertions, 13 deletions

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 42d39116a556..c42b928b15ef 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -428,17 +428,19 @@ int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
 }
 EXPORT_SYMBOL(iov_iter_fault_in_readable);
 
-void iov_iter_init(struct iov_iter *i, int direction,
+void iov_iter_init(struct iov_iter *i, unsigned int direction,
                         const struct iovec *iov, unsigned long nr_segs,
                         size_t count)
 {
+        WARN_ON(direction & ~(READ | WRITE));
+        direction &= READ | WRITE;
+
         /* It will get better.  Eventually... */
         if (uaccess_kernel()) {
-                direction |= ITER_KVEC;
-                i->type = direction;
+                i->type = ITER_KVEC | direction;
                 i->kvec = (struct kvec *)iov;
         } else {
-                i->type = direction;
+                i->type = ITER_IOVEC | direction;
                 i->iov = iov;
         }
         i->nr_segs = nr_segs;
@@ -1060,12 +1062,12 @@ size_t iov_iter_single_seg_count(const struct iov_iter *i)
 }
 EXPORT_SYMBOL(iov_iter_single_seg_count);
 
-void iov_iter_kvec(struct iov_iter *i, int direction,
+void iov_iter_kvec(struct iov_iter *i, unsigned int direction,
                         const struct kvec *kvec, unsigned long nr_segs,
                         size_t count)
 {
-        BUG_ON(!(direction & ITER_KVEC));
-        i->type = direction;
+        WARN_ON(direction & ~(READ | WRITE));
+        i->type = ITER_KVEC | (direction & (READ | WRITE));
         i->kvec = kvec;
         i->nr_segs = nr_segs;
         i->iov_offset = 0;
@@ -1073,12 +1075,12 @@ void iov_iter_kvec(struct iov_iter *i, int direction,
 }
 EXPORT_SYMBOL(iov_iter_kvec);
 
-void iov_iter_bvec(struct iov_iter *i, int direction,
+void iov_iter_bvec(struct iov_iter *i, unsigned int direction,
                         const struct bio_vec *bvec, unsigned long nr_segs,
                         size_t count)
 {
-        BUG_ON(!(direction & ITER_BVEC));
-        i->type = direction;
+        WARN_ON(direction & ~(READ | WRITE));
+        i->type = ITER_BVEC | (direction & (READ | WRITE));
         i->bvec = bvec;
         i->nr_segs = nr_segs;
         i->iov_offset = 0;
@@ -1086,13 +1088,13 @@ void iov_iter_bvec(struct iov_iter *i, int direction,
 }
 EXPORT_SYMBOL(iov_iter_bvec);
 
-void iov_iter_pipe(struct iov_iter *i, int direction,
+void iov_iter_pipe(struct iov_iter *i, unsigned int direction,
                         struct pipe_inode_info *pipe,
                         size_t count)
 {
-        BUG_ON(direction != ITER_PIPE);
+        BUG_ON(direction != READ);
         WARN_ON(pipe->nrbufs == pipe->buffers);
-        i->type = direction;
+        i->type = ITER_PIPE | READ;
         i->pipe = pipe;
         i->idx = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);
         i->iov_offset = 0;