On 11/20/20 5:23 PM, Linus Torvalds wrote:
> On Fri, Nov 20, 2020 at 1:36 PM Jens Axboe <[email protected]> wrote:
>>
>> I don't disagree with you on that. I've been a bit gun shy on touching
>> the VFS side of things, but this one isn't too bad. I hacked up a patch
>> that allows io_uring to do LOOKUP_RCU and a quick test seems to indicate
>> it's fine. On top of that, we just propagate the error if we do fail and
>> get rid of that odd retry loop.
>
> Ok, this looks better to me (but is obviously not 5.10 material).
>
> That said, I think I'd prefer to keep 'struct nameidata' internal to
> just fs/namei.c, and maybe we can just expert that
>
> struct nameidata nd;
>
> set_nameidata(&nd, req->open.dfd, req->open.filename);
> file = path_openat(&nd, &op, op.lookup_flags | LOOKUP_RCU);
> restore_nameidata();
> return filp == ERR_PTR(-ECHILD) ? -EAGAIN : filp;
>
> as a helper from namei.c instead? Call it "do_filp_open_rcu()" or something?
Yes, that's probably a better idea. I'll move in that direction.
> That "force_nonblock" test seems a bit off, though. Why is that RCU
> case only done when "!force_nonblock"? It would seem that if
> force_nonblock is set, you want to do this too?
Taking a second look at it, it's inverted. So if force_nonblock == true,
we want to do just the RCU lookup.
But I think the bit that you're missing is that the other case will do
the normal lookup, which does an RCU lookup first. It looks needs to
look like this:
if (force_nonblock)
file = do_filp_open_rcu();
else
file = do_filp_open();
--
Jens Axboe
