linux-kernel - Re: [PATCH RESEND V12 3/8] fuse: Definitions and ioctl for passthrough

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Date:   Fri, 19 Feb 2021 09:40:21 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Peng Tao <bergwolf@...il.com>
Cc:     Alessio Balsini <balsini@...roid.com>,
        Akilesh Kailash <akailash@...gle.com>,
        Amir Goldstein <amir73il@...il.com>,
        Antonio SJ Musumeci <trapexit@...wn.link>,
        David Anderson <dvander@...gle.com>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Jann Horn <jannh@...gle.com>, Jens Axboe <axboe@...nel.dk>,
        Martijn Coenen <maco@...roid.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Lawrence <paullawrence@...gle.com>,
        Stefano Duo <duostefano93@...il.com>,
        Zimuzo Ezeozue <zezeozue@...gle.com>, wuyan <wu-yan@....com>,
        fuse-devel <fuse-devel@...ts.sourceforge.net>,
        kernel-team <kernel-team@...roid.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND V12 3/8] fuse: Definitions and ioctl for passthrough

On Fri, Feb 19, 2021 at 8:05 AM Peng Tao <bergwolf@...il.com> wrote:
>
> On Wed, Feb 17, 2021 at 9:41 PM Miklos Szeredi <miklos@...redi.hu> wrote:

> > What I think would be useful is to have an explicit
> > FUSE_DEV_IOC_PASSTHROUGH_CLOSE ioctl, that would need to be called
> > once the fuse server no longer needs this ID.   If this turns out to
> > be a performance problem, we could still add the auto-close behavior
> > with an explicit FOPEN_PASSTHROUGH_AUTOCLOSE flag later.
> Hi Miklos,
>
> W/o auto closing, what happens if user space daemon forgets to call
> FUSE_DEV_IOC_PASSTHROUGH_CLOSE? Do we keep the ID alive somewhere?

Kernel would keep the ID open until explicit close or fuse connection
is released.

There should be some limit on the max open files referenced through
ID's, though.   E.g. inherit RLIMIT_NOFILE from mounting task.

Thanks,
Miklos