ITER_PIPE: clean pipe_advance() up

instead of setting ->iov_offset for new position and calling
pipe_truncate() to adjust ->len of the last buffer and discard
everything after it, adjust ->len at the same time we set ->iov_offset
and use pipe_discard_from() to deal with buffers past that.

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

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 95c56d42505b3aaa64ad3e34567f9a32ba186d61..402d49688a169d09e0c2ec626dd203fec43d62a1 100644 (file)
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -845,27 +845,27 @@ static inline void pipe_truncate(struct iov_iter *i)
 static void pipe_advance(struct iov_iter *i, size_t size)
 {
        struct pipe_inode_info *pipe = i->pipe;
-       if (size) {
-               struct pipe_buffer *buf;
-               unsigned int p_mask = pipe->ring_size - 1;
-               unsigned int i_head = i->head;
-               size_t off = i->iov_offset, left = size;
+       unsigned int off = i->iov_offset;
 
+       if (!off && !size) {
+               pipe_discard_from(pipe, i->start_head); // discard everything
+               return;
+       }
+       i->count -= size;
+       while (1) {
+               struct pipe_buffer *buf = pipe_buf(pipe, i->head);
                if (off) /* make it relative to the beginning of buffer */
-                       left += off - pipe->bufs[i_head & p_mask].offset;
-               while (1) {
-                       buf = &pipe->bufs[i_head & p_mask];
-                       if (left <= buf->len)
-                               break;
-                       left -= buf->len;
-                       i_head++;
+                       size += off - buf->offset;
+               if (size <= buf->len) {
+                       buf->len = size;
+                       i->iov_offset = buf->offset + size;
+                       break;
                }
-               i->head = i_head;
-               i->iov_offset = buf->offset + left;
+               size -= buf->len;
+               i->head++;
+               off = 0;
        }
-       i->count -= size;
-       /* ... and discard everything past that point */
-       pipe_truncate(i);
+       pipe_discard_from(pipe, i->head + 1); // discard everything past this one
 }
 
 static void iov_iter_bvec_advance(struct iov_iter *i, size_t size)