switch default_file_splice_read() to use of pipe-backed iov_iter

we only use iov_iter_get_pages_alloc() and iov_iter_advance() -
pages are filled by kernel_readv() via a kvec array (as we used
to do all along), so iov_iter here is used only as a way of
arranging for those pages to be in pipe.

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

diff --git a/fs/splice.c b/fs/splice.c
index 58c322a87f44274b10c3d99f6a0efb0b8248b1fb..0df907ba46ed7eb6c74a351f2eb924f830c10d40 100644 (file)
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -361,7 +361,7 @@ const struct pipe_buf_operations nosteal_pipe_buf_ops = {
 };
 EXPORT_SYMBOL(nosteal_pipe_buf_ops);
 
-static ssize_t kernel_readv(struct file *file, const struct iovec *vec,
+static ssize_t kernel_readv(struct file *file, const struct kvec *vec,
                            unsigned long vlen, loff_t offset)
 {
        mm_segment_t old_fs;
@@ -397,96 +397,65 @@ static ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
                                 struct pipe_inode_info *pipe, size_t len,
                                 unsigned int flags)
 {
+       struct kvec *vec, __vec[PIPE_DEF_BUFFERS];
+       struct iov_iter to;
+       struct page **pages;
        unsigned int nr_pages;
-       unsigned int nr_freed;
-       size_t offset;
-       struct page *pages[PIPE_DEF_BUFFERS];
-       struct partial_page partial[PIPE_DEF_BUFFERS];
-       struct iovec *vec, __vec[PIPE_DEF_BUFFERS];
+       size_t offset, dummy, copied = 0;
        ssize_t res;
-       size_t this_len;
-       int error;
        int i;
-       struct splice_pipe_desc spd = {
-               .pages = pages,
-               .partial = partial,
-               .nr_pages_max = PIPE_DEF_BUFFERS,
-               .flags = flags,
-               .ops = &default_pipe_buf_ops,
-               .spd_release = spd_release_page,
-       };
 
-       if (splice_grow_spd(pipe, &spd))
+       if (pipe->nrbufs == pipe->buffers)
+               return -EAGAIN;
+
+       /*
+        * Try to keep page boundaries matching to source pagecache ones -
+        * it probably won't be much help, but...
+        */
+       offset = *ppos & ~PAGE_MASK;
+
+       iov_iter_pipe(&to, ITER_PIPE | READ, pipe, len + offset);
+
+       res = iov_iter_get_pages_alloc(&to, &pages, len + offset, &dummy);
+       if (res <= 0)
                return -ENOMEM;
 
-       res = -ENOMEM;
+       nr_pages = res / PAGE_SIZE;
+
        vec = __vec;
-       if (spd.nr_pages_max > PIPE_DEF_BUFFERS) {
-               vec = kmalloc(spd.nr_pages_max * sizeof(struct iovec), GFP_KERNEL);
-               if (!vec)
-                       goto shrink_ret;
+       if (nr_pages > PIPE_DEF_BUFFERS) {
+               vec = kmalloc(nr_pages * sizeof(struct kvec), GFP_KERNEL);
+               if (unlikely(!vec)) {
+                       res = -ENOMEM;
+                       goto out;
+               }
        }
 
-       offset = *ppos & ~PAGE_MASK;
-       nr_pages = (len + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
-
-       for (i = 0; i < nr_pages && i < spd.nr_pages_max && len; i++) {
-               struct page *page;
-
-               page = alloc_page(GFP_USER);
-               error = -ENOMEM;
-               if (!page)
-                       goto err;
+       pipe->bufs[to.idx].offset = offset;
+       pipe->bufs[to.idx].len -= offset;
 
-               this_len = min_t(size_t, len, PAGE_SIZE - offset);
-               vec[i].iov_base = (void __user *) page_address(page);
+       for (i = 0; i < nr_pages; i++) {
+               size_t this_len = min_t(size_t, len, PAGE_SIZE - offset);
+               vec[i].iov_base = page_address(pages[i]) + offset;
                vec[i].iov_len = this_len;
-               spd.pages[i] = page;
-               spd.nr_pages++;
                len -= this_len;
                offset = 0;
        }
 
-       res = kernel_readv(in, vec, spd.nr_pages, *ppos);
-       if (res < 0) {
-               error = res;
-               goto err;
-       }
-
-       error = 0;
-       if (!res)
-               goto err;
-
-       nr_freed = 0;
-       for (i = 0; i < spd.nr_pages; i++) {
-               this_len = min_t(size_t, vec[i].iov_len, res);
-               spd.partial[i].offset = 0;
-               spd.partial[i].len = this_len;
-               if (!this_len) {
-                       __free_page(spd.pages[i]);
-                       spd.pages[i] = NULL;
-                       nr_freed++;
-               }
-               res -= this_len;
-       }
-       spd.nr_pages -= nr_freed;
-
-       res = splice_to_pipe(pipe, &spd);
-       if (res > 0)
+       res = kernel_readv(in, vec, nr_pages, *ppos);
+       if (res > 0) {
+               copied = res;
                *ppos += res;
+       }
 
-shrink_ret:
        if (vec != __vec)
                kfree(vec);
-       splice_shrink_spd(&spd);
+out:
+       for (i = 0; i < nr_pages; i++)
+               put_page(pages[i]);
+       kvfree(pages);
+       iov_iter_advance(&to, copied);  /* truncates and discards */
        return res;
-
-err:
-       for (i = 0; i < spd.nr_pages; i++)
-               __free_page(spd.pages[i]);
-
-       res = error;
-       goto shrink_ret;
 }
 
 /*