+/*
+ * writepage: Called from one of two places:
+ *
+ * 1. we are flushing a delalloc buffer head.
+ *
+ * 2. we are writing out a dirty page. Typically the page dirty
+ * state is cleared before we get here. In this case is it
+ * conceivable we have no buffer heads.
+ *
+ * For delalloc space on the page we need to allocate space and
+ * flush it. For unmapped buffer heads on the page we should
+ * allocate space if the page is uptodate. For any other dirty
+ * buffer heads on the page we should flush them.
+ *
+ * If we detect that a transaction would be required to flush
+ * the page, we have to check the process flags first, if we
+ * are already in a transaction or disk I/O during allocations
+ * is off, we need to fail the writepage and redirty the page.
+ */
+
+STATIC int
+xfs_vm_writepage(
+ struct page *page,
+ struct writeback_control *wbc)
+{
+ int error;
+ int need_trans;
+ int delalloc, unmapped, unwritten;
+ struct inode *inode = page->mapping->host;
+
+ xfs_page_trace(XFS_WRITEPAGE_ENTER, inode, page, 0);
+
+ /*
+ * We need a transaction if:
+ * 1. There are delalloc buffers on the page
+ * 2. The page is uptodate and we have unmapped buffers
+ * 3. The page is uptodate and we have no buffers
+ * 4. There are unwritten buffers on the page
+ */
+
+ if (!page_has_buffers(page)) {
+ unmapped = 1;
+ need_trans = 1;
+ } else {
+ xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);
+ if (!PageUptodate(page))
+ unmapped = 0;
+ need_trans = delalloc + unmapped + unwritten;
+ }
+
+ /*
+ * If we need a transaction and the process flags say
+ * we are already in a transaction, or no IO is allowed
+ * then mark the page dirty again and leave the page
+ * as is.
+ */
+ if (current_test_flags(PF_FSTRANS) && need_trans)
+ goto out_fail;
+
+ /*
+ * Delay hooking up buffer heads until we have
+ * made our go/no-go decision.
+ */
+ if (!page_has_buffers(page))
+ create_empty_buffers(page, 1 << inode->i_blkbits, 0);
+
+ /*
+ * Convert delayed allocate, unwritten or unmapped space
+ * to real space and flush out to disk.
+ */
+ error = xfs_page_state_convert(inode, page, wbc, 1, unmapped);
+ if (error == -EAGAIN)
+ goto out_fail;
+ if (unlikely(error < 0))
+ goto out_unlock;
+
+ return 0;
+
+out_fail:
+ redirty_page_for_writepage(wbc, page);
+ unlock_page(page);
+ return 0;
+out_unlock:
+ unlock_page(page);
+ return error;
+}
+
+STATIC int
+xfs_vm_writepages(
+ struct address_space *mapping,
+ struct writeback_control *wbc)
+{
+ struct bhv_vnode *vp = vn_from_inode(mapping->host);
+
+ if (VN_TRUNC(vp))
+ VUNTRUNCATE(vp);
+ return generic_writepages(mapping, wbc);
+}
+
+/*
+ * Called to move a page into cleanable state - and from there
+ * to be released. Possibly the page is already clean. We always
+ * have buffer heads in this call.
+ *
+ * Returns 0 if the page is ok to release, 1 otherwise.
+ *
+ * Possible scenarios are:
+ *
+ * 1. We are being called to release a page which has been written
+ * to via regular I/O. buffer heads will be dirty and possibly
+ * delalloc. If no delalloc buffer heads in this case then we
+ * can just return zero.
+ *
+ * 2. We are called to release a page which has been written via
+ * mmap, all we need to do is ensure there is no delalloc
+ * state in the buffer heads, if not we can let the caller
+ * free them and we should come back later via writepage.
+ */
+STATIC int
+xfs_vm_releasepage(
+ struct page *page,
+ gfp_t gfp_mask)
+{
+ struct inode *inode = page->mapping->host;
+ int dirty, delalloc, unmapped, unwritten;
+ struct writeback_control wbc = {
+ .sync_mode = WB_SYNC_ALL,
+ .nr_to_write = 1,
+ };
+
+ xfs_page_trace(XFS_RELEASEPAGE_ENTER, inode, page, 0);
+
+ if (!page_has_buffers(page))
+ return 0;
+
+ xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);
+ if (!delalloc && !unwritten)
+ goto free_buffers;
+
+ if (!(gfp_mask & __GFP_FS))
+ return 0;
+
+ /* If we are already inside a transaction or the thread cannot
+ * do I/O, we cannot release this page.
+ */
+ if (current_test_flags(PF_FSTRANS))
+ return 0;
+
+ /*
+ * Convert delalloc space to real space, do not flush the
+ * data out to disk, that will be done by the caller.
+ * Never need to allocate space here - we will always
+ * come back to writepage in that case.
+ */
+ dirty = xfs_page_state_convert(inode, page, &wbc, 0, 0);
+ if (dirty == 0 && !unwritten)
+ goto free_buffers;
+ return 0;
+
+free_buffers:
+ return try_to_free_buffers(page);
+}
+