ITER_PIPE: helpers for adding pipe buffers

There are only two kinds of pipe_buffer in the area used by ITER_PIPE.

1) anonymous - copy_to_iter() et.al. end up creating those and copying
data there.  They have zero ->offset, and their ->ops points to
default_pipe_page_ops.

2) zero-copy ones - those come from copy_page_to_iter(), and page
comes from caller.  ->offset is also caller-supplied - it might be
non-zero.  ->ops points to page_cache_pipe_buf_ops.

Move creation and insertion of those into helpers - push_anon(pipe, size)
and push_page(pipe, page, offset, size) resp., separating them from
the "could we avoid creating a new buffer by merging with the current
head?" logics.

Acked-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 048026d5aa0d2e36ddf2e7e5e43c21f0da55f857..a5c436e564e8e7b3b0de337ba44853fddccb5d52 100644 (file)
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -231,15 +231,39 @@ Bad:
 #define sanity(i) true
 #endif
 
+static struct page *push_anon(struct pipe_inode_info *pipe, unsigned size)
+{
+       struct page *page = alloc_page(GFP_USER);
+       if (page) {
+               struct pipe_buffer *buf = pipe_buf(pipe, pipe->head++);
+               *buf = (struct pipe_buffer) {
+                       .ops = &default_pipe_buf_ops,
+                       .page = page,
+                       .offset = 0,
+                       .len = size
+               };
+       }
+       return page;
+}
+
+static void push_page(struct pipe_inode_info *pipe, struct page *page,
+                       unsigned int offset, unsigned int size)
+{
+       struct pipe_buffer *buf = pipe_buf(pipe, pipe->head++);
+       *buf = (struct pipe_buffer) {
+               .ops = &page_cache_pipe_buf_ops,
+               .page = page,
+               .offset = offset,
+               .len = size
+       };
+       get_page(page);
+}
+
 static size_t copy_page_to_iter_pipe(struct page *page, size_t offset, size_t bytes,
                         struct iov_iter *i)
 {
        struct pipe_inode_info *pipe = i->pipe;
-       struct pipe_buffer *buf;
-       unsigned int p_tail = pipe->tail;
-       unsigned int p_mask = pipe->ring_size - 1;
-       unsigned int i_head = i->head;
-       size_t off;
+       unsigned int head = pipe->head;
 
        if (unlikely(bytes > i->count))
                bytes = i->count;
@@ -250,32 +274,21 @@ static size_t copy_page_to_iter_pipe(struct page *page, size_t offset, size_t by
        if (!sanity(i))
                return 0;
 
-       off = i->iov_offset;
-       buf = &pipe->bufs[i_head & p_mask];
-       if (off) {
-               if (offset == off && buf->page == page) {
-                       /* merge with the last one */
+       if (offset && i->iov_offset == offset) { // could we merge it?
+               struct pipe_buffer *buf = pipe_buf(pipe, head - 1);
+               if (buf->page == page) {
                        buf->len += bytes;
                        i->iov_offset += bytes;
-                       goto out;
+                       i->count -= bytes;
+                       return bytes;
                }
-               i_head++;
-               buf = &pipe->bufs[i_head & p_mask];
        }
-       if (pipe_full(i_head, p_tail, pipe->max_usage))
+       if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
                return 0;
 
-       buf->ops = &page_cache_pipe_buf_ops;
-       buf->flags = 0;
-       get_page(page);
-       buf->page = page;
-       buf->offset = offset;
-       buf->len = bytes;
-
-       pipe->head = i_head + 1;
+       push_page(pipe, page, offset, bytes);
        i->iov_offset = offset + bytes;
-       i->head = i_head;
-out:
+       i->head = head;
        i->count -= bytes;
        return bytes;
 }
@@ -407,8 +420,6 @@ static size_t push_pipe(struct iov_iter *i, size_t size,
                        int *iter_headp, size_t *offp)
 {
        struct pipe_inode_info *pipe = i->pipe;
-       unsigned int p_tail = pipe->tail;
-       unsigned int p_mask = pipe->ring_size - 1;
        unsigned int iter_head;
        size_t off;
        ssize_t left;
@@ -423,30 +434,23 @@ static size_t push_pipe(struct iov_iter *i, size_t size,
        *iter_headp = iter_head;
        *offp = off;
        if (off) {
+               struct pipe_buffer *buf = pipe_buf(pipe, iter_head);
+
                left -= PAGE_SIZE - off;
                if (left <= 0) {
-                       pipe->bufs[iter_head & p_mask].len += size;
+                       buf->len += size;
                        return size;
                }
-               pipe->bufs[iter_head & p_mask].len = PAGE_SIZE;
-               iter_head++;
+               buf->len = PAGE_SIZE;
        }
-       while (!pipe_full(iter_head, p_tail, pipe->max_usage)) {
-               struct pipe_buffer *buf = &pipe->bufs[iter_head & p_mask];
-               struct page *page = alloc_page(GFP_USER);
+       while (!pipe_full(pipe->head, pipe->tail, pipe->max_usage)) {
+               struct page *page = push_anon(pipe,
+                                             min_t(ssize_t, left, PAGE_SIZE));
                if (!page)
                        break;
 
-               buf->ops = &default_pipe_buf_ops;
-               buf->flags = 0;
-               buf->page = page;
-               buf->offset = 0;
-               buf->len = min_t(ssize_t, left, PAGE_SIZE);
-               left -= buf->len;
-               iter_head++;
-               pipe->head = iter_head;
-
-               if (left == 0)
+               left -= PAGE_SIZE;
+               if (left <= 0)
                        return size;
        }
        return size - left;