On Tue, Nov 21, 2023 at 11:26:15AM +0530, Ritesh Harjani wrote: > > instantly spot anything that relies on them - you are just a lot more > > likely to hit an -ENOSPC from ->map_blocks now. > > Which is also true with existing code no? If the block reservation is > not done at the write fault, writeback is likely to fail due to ENOSPC? Yes. Not saying you should change this, I just want to make sure the iomap code handles this fine. I think it does, but I'd rather be sure. > Sure, make sense. Thanks! > I can try and check if the the wrapper helps. Let's wait until we have a few more conversions. > > Did yo run into issues in using the iomap based aops for the other uses > > of ext2_aops, or are just trying to address the users one at a time? > > There are problems for e.g. for dir type in ext2. It uses the pagecache > for dir. It uses buffer_heads and attaches them to folio->private. > ...it uses block_write_begin/block_write_end() calls. > Look for ext4_make_empty() -> ext4_prepare_chunk -> > block_write_begin(). > Now during sync/writeback of the dirty pages (ext4_handle_dirsync()), we > might take a iomap writeback path (if using ext2_file_aops for dir) > which sees folio->private assuming it is "struct iomap_folio_state". > And bad things will happen... Oh, indeed, bufferheads again. > Now we don't have an equivalent APIs in iomap for > block_write_begin()/end() which the users can call for. Hence, Jan > suggested to lets first convert ext2 regular file path to iomap as an RFC. Yes, no problem. But maybe worth documenting in the commit log.
