+static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
+ struct pipe_inode_info *pipe, size_t len,
+ unsigned int flags)
+{
+ struct address_space *mapping = in->f_mapping;
+ struct inode *inode = mapping->host;
+ unsigned int loff, nr_pages, req_pages;
+ struct page *pages[PIPE_DEF_BUFFERS];
+ struct partial_page partial[PIPE_DEF_BUFFERS];
+ struct page *page;
+ pgoff_t index, end_index;
+ loff_t isize, left;
+ int error, page_nr;
+ struct splice_pipe_desc spd = {
+ .pages = pages,
+ .partial = partial,
+ .flags = flags,
+ .ops = &page_cache_pipe_buf_ops,
+ .spd_release = spd_release_page,
+ };
+
+ isize = i_size_read(inode);
+ if (unlikely(*ppos >= isize))
+ return 0;
+
+ left = isize - *ppos;
+ if (unlikely(left < len))
+ len = left;
+
+ if (splice_grow_spd(pipe, &spd))
+ return -ENOMEM;
+
+ index = *ppos >> PAGE_CACHE_SHIFT;
+ loff = *ppos & ~PAGE_CACHE_MASK;
+ req_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+ nr_pages = min(req_pages, pipe->buffers);
+
+ spd.nr_pages = find_get_pages_contig(mapping, index,
+ nr_pages, spd.pages);
+ index += spd.nr_pages;
+ error = 0;
+
+ while (spd.nr_pages < nr_pages) {
+ error = shmem_getpage(inode, index, &page, SGP_CACHE, NULL);
+ if (error)
+ break;
+ unlock_page(page);
+ spd.pages[spd.nr_pages++] = page;
+ index++;
+ }
+
+ index = *ppos >> PAGE_CACHE_SHIFT;
+ nr_pages = spd.nr_pages;
+ spd.nr_pages = 0;
+
+ for (page_nr = 0; page_nr < nr_pages; page_nr++) {
+ unsigned int this_len;
+
+ if (!len)
+ break;
+
+ this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
+ page = spd.pages[page_nr];
+
+ if (!PageUptodate(page) || page->mapping != mapping) {
+ error = shmem_getpage(inode, index, &page,
+ SGP_CACHE, NULL);
+ if (error)
+ break;
+ unlock_page(page);
+ page_cache_release(spd.pages[page_nr]);
+ spd.pages[page_nr] = page;
+ }
+
+ isize = i_size_read(inode);
+ end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
+ if (unlikely(!isize || index > end_index))
+ break;
+
+ if (end_index == index) {
+ unsigned int plen;
+
+ plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
+ if (plen <= loff)
+ break;
+
+ this_len = min(this_len, plen - loff);
+ len = this_len;
+ }
+
+ spd.partial[page_nr].offset = loff;
+ spd.partial[page_nr].len = this_len;
+ len -= this_len;
+ loff = 0;
+ spd.nr_pages++;
+ index++;
+ }
+
+ while (page_nr < nr_pages)
+ page_cache_release(spd.pages[page_nr++]);
+
+ if (spd.nr_pages)
+ error = splice_to_pipe(pipe, &spd);
+
+ splice_shrink_spd(pipe, &spd);
+
+ if (error > 0) {
+ *ppos += error;
+ file_accessed(in);
+ }
+ return error;
+}
+