fs: convert __generic_file_fsync to use errseq_t based reporting

Many simple, block-based filesystems use generic_file_fsync as their
fsync operation. Some others (ext* and fat) also call this function
to handle syncing out data.

Switch this code over to use errseq_t based error reporting so that
all of these filesystems get reliable error reporting via fsync,
fdatasync and msync.

Signed-off-by: Jeff Layton <[e-mail]>

fs/libfs.c

···
 	int err;
 	int ret;
 
-	err = filemap_write_and_wait_range(inode->i_mapping, start, end);
+	err = file_write_and_wait_range(file, start, end);
 	if (err)
 		return err;
 
···
 
 out:
 	inode_unlock(inode);
-	/* must call this unconditionally as it clears AS_* error flags */
-	err = filemap_check_errors(inode->i_mapping);
-	return ret ? ret : err;
+	/* check and advance again to catch errors after syncing out buffers */
+	err = file_check_and_advance_wb_err(file);
+	if (ret == 0)
+		ret = err;
+	return ret;
 }
 EXPORT_SYMBOL(__generic_file_fsync);