BUG：dir_idx in lwext which is used by libext

[Luca-Cliver]

I attempted to create a large number of files using libext to test the directory indexing mechanism. However, when the number of files exceeded a certain threshold, the file system threw an error indicating a mismatch between the limit and entry_space fields in the directory entry block.The code in the screenshot is part of the dir_dx_get_leaf function, and I added a debug print statement to it.

This indicates that the limit is larger than expected. I found the issue in the function where the directory index block is split.

Here, node_limit is computed before subtracting the space for the checksum tail, making it too large when meta_csum is enabled.The commented line of code is my fix. When validation is enabled, I recalculate the space here and then write the limit. This resolves the issue mentioned earlier. I only captured one part in the screenshot, but in reality, there are two places where this occurs. The two child index blocks created during the split both have this issue.

I believe this solution is more appropriate. I kindly request the senior developers to review it. If the issue was caused by an error on my part, I would be grateful if you could point it out. Apologies for taking up your time.

[nyh]

@wkozaczuk you wrote this ext4 support, maybe you can take a look.
@Luca-Cliver if there is a solution you'd like to propose please send a patch (you can do this in the form of a pull-request) and it will make it easier to review. Thanks!

[wkozaczuk]

@Luca-Cliver Based on what I see, the bug you are reporting seems to be located in the https://github.com/gkostka/lwext4, which the OSv libext module wraps around. More specifically, it is in the function ext4_dir_dx_split_index of the src/ext4_dir_idx.c?

Ideally, this should be reported against https://github.com/gkostka/lwext4, but from what I can tell, this library does not seem to be maintained anymore (you can try), and actually, we have our own clone - https://github.com/osvunikernel/lwext4.

I think you are correct about the solution, so I suggest you create a proper PR against https://github.com/osvunikernel/lwext4 with the changes and ideally a test to illustrate how you fix the issue.

BTW I have fixed another issue in the same place - see osvunikernel/lwext4@c6fed65.