+static inline loff_t page_seek_hole_data(struct xa_state *xas,
+ struct address_space *mapping, struct page *page,
+ loff_t start, loff_t end, bool seek_data)
+{
+ const struct address_space_operations *ops = mapping->a_ops;
+ size_t offset, bsz = i_blocksize(mapping->host);
+
+ if (xa_is_value(page) || PageUptodate(page))
+ return seek_data ? start : end;
+ if (!ops->is_partially_uptodate)
+ return seek_data ? end : start;
+
+ xas_pause(xas);
+ rcu_read_unlock();
+ lock_page(page);
+ if (unlikely(page->mapping != mapping))
+ goto unlock;
+
+ offset = offset_in_thp(page, start) & ~(bsz - 1);
+
+ do {
+ if (ops->is_partially_uptodate(page, offset, bsz) == seek_data)
+ break;
+ start = (start + bsz) & ~(bsz - 1);
+ offset += bsz;
+ } while (offset < thp_size(page));
+unlock:
+ unlock_page(page);
+ rcu_read_lock();
+ return start;
+}
+
+static inline
+unsigned int seek_page_size(struct xa_state *xas, struct page *page)
+{
+ if (xa_is_value(page))
+ return PAGE_SIZE << xa_get_order(xas->xa, xas->xa_index);
+ return thp_size(page);
+}
+
+/**
+ * mapping_seek_hole_data - Seek for SEEK_DATA / SEEK_HOLE in the page cache.
+ * @mapping: Address space to search.
+ * @start: First byte to consider.
+ * @end: Limit of search (exclusive).
+ * @whence: Either SEEK_HOLE or SEEK_DATA.
+ *
+ * If the page cache knows which blocks contain holes and which blocks
+ * contain data, your filesystem can use this function to implement
+ * SEEK_HOLE and SEEK_DATA. This is useful for filesystems which are
+ * entirely memory-based such as tmpfs, and filesystems which support
+ * unwritten extents.
+ *
+ * Return: The requested offset on successs, or -ENXIO if @whence specifies
+ * SEEK_DATA and there is no data after @start. There is an implicit hole
+ * after @end - 1, so SEEK_HOLE returns @end if all the bytes between @start
+ * and @end contain data.
+ */
+loff_t mapping_seek_hole_data(struct address_space *mapping, loff_t start,
+ loff_t end, int whence)
+{
+ XA_STATE(xas, &mapping->i_pages, start >> PAGE_SHIFT);
+ pgoff_t max = (end - 1) / PAGE_SIZE;
+ bool seek_data = (whence == SEEK_DATA);
+ struct page *page;
+
+ if (end <= start)
+ return -ENXIO;
+
+ rcu_read_lock();
+ while ((page = find_get_entry(&xas, max, XA_PRESENT))) {
+ loff_t pos = xas.xa_index * PAGE_SIZE;
+
+ if (start < pos) {
+ if (!seek_data)
+ goto unlock;
+ start = pos;
+ }
+
+ pos += seek_page_size(&xas, page);
+ start = page_seek_hole_data(&xas, mapping, page, start, pos,
+ seek_data);
+ if (start < pos)
+ goto unlock;
+ if (!xa_is_value(page))
+ put_page(page);
+ }
+ rcu_read_unlock();
+
+ if (seek_data)
+ return -ENXIO;
+ goto out;
+
+unlock:
+ rcu_read_unlock();
+ if (!xa_is_value(page))
+ put_page(page);
+out:
+ if (start > end)
+ return end;
+ return start;
+}
+