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From:   Keiichi Watanabe <keiichiw@chromium.org>
Date:   Wed, 21 Jun 2023 18:40:21 +0900
Message-ID: <CAD90VcZeoagh7a-0qA1SudJ3v53fvyr7t2iwGx_+dnAL7M=jnw@mail.gmail.com>
Subject: Re: [PATCH 2/3] fuse: Add negative_dentry_timeout option
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     =?UTF-8?B?SnVuaWNoaSBVZWthd2EgKOS4iuW3nee0lOS4gCk=?= 
        <uekawa@google.com>, LKML <linux-kernel@vger.kernel.org>,
        mhiramat@google.com, takayas@chromium.org, drosen@google.com,
        sarthakkukreti@google.com, Jonathan Corbet <corbet@lwn.net>,
        linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org
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On Wed, Jun 21, 2023 at 1:07=E2=80=AFPM Miklos Szeredi <miklos@szeredi.hu> =
wrote:
>
> On Wed, 21 Jun 2023 at 00:53, Junichi Uekawa (=E4=B8=8A=E5=B7=9D=E7=B4=94=
=E4=B8=80) <uekawa@google.com> wrote:
> >
> > Hi
> >
> >
> >
> > 2023=E5=B9=B46=E6=9C=8821=E6=97=A5(=E6=B0=B4) 4:28 Miklos Szeredi <mikl=
os@szeredi.hu>:
> >>
> >> On Tue, 20 Jun 2023 at 17:14, Keiichi Watanabe <keiichiw@chromium.org>=
 wrote:
> >> >
> >> > Add `negative_dentry_timeout` mount option for FUSE to cache negativ=
e
> >> > dentries for the specified duration.
> >>
> >> This is already possible, no kernel changes needed.  See e.g.
> >> xmp_init() in libfuse/example/passthrough.c.
> >>
> >
> > Thank you for the pointer!
> >
> > So reading libfuse/fuse.c, fuse_lib_lookup does a reply with e.ino=3D0 =
err=3D0 (instead of ENOENT) with e.entry_timeout=3Dnegative_timeout,
> > for each lookup (and there's no global configuration but that's okay) ?
>
> Yes.


Oh, good to know!
I could make it work in our VMM (crosvm) without any kernel changes.
https://crrev.com/c/4630879
Thanks a lot!

Keiichi


>
>
> Thanks,
> Miklos