On 2021/7/27 15:38, Eric Biggers wrote:
That's somewhat helpful, but I've been doing some more investigation and now I'm even more confused. How can f2fs support non-overwrite DIO writes at all (meaning DIO writes in LFS mode as well as DIO writes to holes in non-LFS mode), given that it has no support for unwritten extents? AFAICS, as-is users can
I'm trying to pick up DAX support patch created by Qiuyang from huawei, and it looks it faces the same issue, so it tries to fix this by calling sb_issue_zeroout() in f2fs_map_blocks() before it returns.
easily leak uninitialized disk contents on f2fs by issuing a DIO write that won't complete fully (or might not complete fully), then reading back the blocks that got allocated but not written to. I think that f2fs will have to take the ext2 approach of not allowing non-overwrite DIO writes at all...
Yes, Another option is to enhance f2fs metadata's scalability which needs to update layout of dnode block or SSA block, after that we can record the status of unwritten data block there... it's a big change though... Thanks,
- Eric
