Re: [PATCH] eventfs: Stop using dcache_readdir() for getdents()

[Linus Torvalds]

On Wed, 3 Jan 2024 at 14:04, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> I actually have something almost working too. Here's the WIP. It only works
> for tracefs, and now eventfs needs to be updated as the "events" directory
> no longer has the right ownership. So I need a way to link the eventfs
> entries to use the tracefs default conditionally.

Ack. So the ->getattr() and ->permission() thing is a bit more
targeted to "look at modes", and is probably better just for that
reason.

Doing it in d_revalidate() is a bit hacky, and impacts path lookup a
bit even when not necessary. But it's still a lot less evil than
walking the dentry tree manually.

So that d_revalidate() patch was more of a "I think you can make it
smaller by just hooking in at this layer"). So d_revalidate ends up
with a smaller patch, I think, but it has the problem that now you
*have* to be able to deal with things in RCU context.

In contrast, doing it in ->getattr() and ->permission() ends up
meaning you can use sleeping locks etc if you need to serialize, for
example. So it's a bit more specific to the whole issue of "deal with
modes and owndership", but it is *also* a bit more flexible in how you
can then do it.

Anyway, your patch looks fine from a quick scan.

                  Linus