fuse: Flush files on wb close

Any write request requires a file handle to report to the userspace. Thus
when we close a file (and free the fuse_file with this info) we have to
flush all the outstanding dirty pages.

filemap_write_and_wait() is enough because every page under fuse writeback
is accounted in ff->count. This delays actual close until all fuse wb is
completed.

In case of "write cache" turned off, the flush is ensured by fuse_vma_close().
Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/fuse/file.c

@@ -308,6 +308,12 @@ static int fuse_open(struct inode *inode, struct file *file)
 
 static int fuse_release(struct inode *inode, struct file *file)
 {
+	struct fuse_conn *fc = get_fuse_conn(inode);
+
+	/* see fuse_vma_close() for !writeback_cache case */
+	if (fc->writeback_cache)
+		filemap_write_and_wait(file->f_mapping);
+
 	if (test_bit(FUSE_I_MTIME_DIRTY, &get_fuse_inode(inode)->state))
 		fuse_flush_mtime(file, true);