Re: open()ing a directory without O_DIRECTORY

> On Mar 3, 2019, at 2:17 PM, Aymeric Vincent <[email protected]> wrote:
> 
> [email protected] (Christos Zoulas) writes:
> 
>> In article <[email protected]>,
>> Aymeric Vincent  <[email protected]> wrote:
>>> 
>>> There is no trivial way to get rid of this no longer valid contents,
>>> since for good reason you can't write to a directory as a file. You have
>>> to re-create it (not always possible due to permissions) or create long
>>> entries until your data disappears... :-/
>> 
>> Why? The kernel can just zero out the deleted dirents.
> 
> Forgot to mention: "in the current situation". And yes, that's exactly
> what I think, probably the alternative is
> 
> - zero out on unlink() so that the data is no longer on the disk
>   (Everybody seems to have expressed preference for this solution but I
>   think this requires changing all the affected filesystems)
> - zero out in getdents() so that the data cannot be accessed without
>   accessing the raw device, mimicking the behaviour of unlink for the
>   data: data still present on disk but not accessible without accessing
>   the raw device. (This requires forbidding read() and similar on
>   directories)

Well, even if you zero out the new entries as you delete them, you need
to have a way to update filesystems that have old unclean directories.
Perhaps we can have fsck do it, or even better have way (through fcntl/ioctl/
new syscall/or even abusing open flags) to clean and/or
compact an existing directory (which we cannot do right now).

I am not opposed to changing O_DIRECTORY to be required to open
directories (and overriding globally via sysctl), but that does not fix the
underlying issue.

christos