Re: [PATCH 0/5] samples/kernfs: Add a pseudo-filesystem to demonstrate kernfs usage

[David Reaver <me@davidreaver.com>]

Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:

> On Tue, Jan 28, 2025 at 07:02:24PM -0500, Steven Rostedt wrote:
>>
>> And eventfs goes one step further. Because there's a full directory layout
>> that's identical for every event, it has a single descriptor for directory
>> and not for file. As there can be over 10 files per directory/event I
>> didn't want to waste even that memory. This is why I couldn't use kernfs
>> for eventfs, as I was able to still save a couple of megabytes by not
>> having the files have any descriptor representing them (besides a single
>> array for all events).
>
> Ok, that's fine, but the original point of "are you sure you want to use
> kernfs for anything other than what we have today" remains.  It's only a
> limited set of use cases that kernfs is good for, libfs is still the
> best place to start out for a virtual filesystem.  The fact that the
> majority of our "fake" filesystems are using libfs and not kernfs is
> semi-proof of that?
>
> Or is it proof that kernfs is just too undocumented that no one wants to
> move to it?  I don't know, but adding samples like this really isn't the
> answer to that, the answer would be moving an existing libfs
> implementation to use kernfs and then that patch series would be the
> example to follow for others.
>
> thanks,
>
> greg k-h

Thanks for reviewing the patch, Greg!

I put this sample together with the idea that some documentation is
better than none. I researched how kernfs could be useful in tracefs and
debugfs, but I haven't looked deeply into other virtual filesystems, so
I may have overestimated how well kernfs fits other use cases. From this
discussion, I see that a real libfs-to-kernfs port would provide a
better understanding of kernfs' viability elsewhere and also serve as
documentation.

Thanks for the discussion, folks! I learned a lot from this thread.

Thanks,
David Reaver