> isofs does support read_iter, without that it would not have worked > before either. That is not the problem. It must be related to > the FMODE_WRITE check - i.e. we have a writable FD here, but a file > system that does not actually supports writes. Which honestly feels > weird, but we'll have to figure it out to unbreak these setups. If it is a directory, isofs_dir_operations is used. In this case, isofs does not support read_iter (I used a directory when testing). If it is a regular file, generic_ro_fops is used. In this case, isofs supports read_iter. When a regular file has a writable attribute, the problem will recur because isofs does not support write_iter.
