From: Alessio Balsini <balsini@android.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Peng Tao <bergwolf@gmail.com>,
Alessio Balsini <balsini@android.com>,
Akilesh Kailash <akailash@google.com>,
Amir Goldstein <amir73il@gmail.com>,
Antonio SJ Musumeci <trapexit@spawn.link>,
David Anderson <dvander@google.com>,
Giuseppe Scrivano <gscrivan@redhat.com>,
Jann Horn <jannh@google.com>, Jens Axboe <axboe@kernel.dk>,
Martijn Coenen <maco@android.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Paul Lawrence <paullawrence@google.com>,
Stefano Duo <duostefano93@gmail.com>,
Zimuzo Ezeozue <zezeozue@google.com>, wuyan <wu-yan@tcl.com>,
fuse-devel <fuse-devel@lists.sourceforge.net>,
kernel-team <kernel-team@android.com>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RESEND V12 3/8] fuse: Definitions and ioctl for passthrough
Date: Mon, 1 Mar 2021 17:05:01 +0000 [thread overview]
Message-ID: <YD0evc676pdANlHQ@google.com> (raw)
In-Reply-To: <CAJfpegtmXegm0FFxs-rs6UhJq4raktiyuzO483wRatj5HKZvYA@mail.gmail.com>
On Fri, Feb 19, 2021 at 09:40:21AM +0100, Miklos Szeredi wrote:
> On Fri, Feb 19, 2021 at 8:05 AM Peng Tao <bergwolf@gmail.com> wrote:
> >
> > On Wed, Feb 17, 2021 at 9:41 PM Miklos Szeredi <miklos@szeredi.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
I like the idea of FUSE_DEV_IOC_PASSTHROUGH_CLOSE to revoke the
passthrough access, that is something I was already working on. What I
had in mind was simply to break that 1:1 connection between fuse_file
and lower filp setting a specific fuse_file::passthrough::filp to NULL,
but this is slightly different from what you mentioned.
AFAIU you are suggesting to allocate one ID for each lower fs file
opened with passthrough within a connection, and maybe using idr_find at
every read/write/mmap operation to check if passthrough is enabled on
that file. Something similar to fuse2_map_get().
This way the fuse server can pass the same ID to one or more
fuse_file(s).
FUSE_DEV_IOC_PASSTHROUGH_CLOSE would idr_remove the ID, so idr_find
would fail, preventing the use of passthrough on that ID. CMIIW.
After FUSE_DEV_IOC_PASSTHROUGH_CLOSE(ID) it may happen that if some
fuse_file(s) storing that ID are still open and the same ID is reclaimed
in a new idr_alloc, this would lead to mismatching lower fs filp being
used by our fuse_file(s). So also the ID stored in the fuse_file(s)
must be invalidated to prevent future uses of deallocated IDs.
Would it make sense to have a list of fuse_files using the same ID, that
must be traversed at FUSE_DEV_IOC_PASSTHROUGH_CLOSE time?
Negative values (maybe -ENOENT) might be used to mark IDs as invalid,
and tested before idr_find at read/write/mmap to avoid the idr_find
complexity in case passthrough is disabled for that file.
What do you think?
I agree with all the above comments to this patch, i.e., add
FOPEN_PASSTHROUGH, drop fuse_passthrough_out, header version+changelog,
that will be fixed in V13.
Thanks,
Alessio
next prev parent reply other threads:[~2021-03-01 20:24 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-25 15:30 [PATCH RESEND V12 0/8] fuse: Add support for passthrough read/write Alessio Balsini
2021-01-25 15:30 ` [PATCH RESEND V12 1/8] fs: Generic function to convert iocb to rw flags Alessio Balsini
2021-01-25 16:46 ` Alessio Balsini
2021-03-24 7:43 ` Rokudo Yan
2021-03-24 14:02 ` Alessio Balsini
2021-01-25 15:30 ` [PATCH RESEND V12 2/8] fuse: 32-bit user space ioctl compat for fuse device Alessio Balsini
[not found] ` <CAMAHBGzkfEd9-1u0iKXp65ReJQgUi_=4sMpmfkwEOaMp6Ux7pg@mail.gmail.com>
2021-01-27 13:40 ` Alessio Balsini
[not found] ` <CAMAHBGwpKW+30kNQ_Apt8A-FTmr94hBOzkT21cjEHHW+t7yUMQ@mail.gmail.com>
2021-01-28 14:15 ` Alessio Balsini
2021-02-05 9:54 ` Peng Tao
2021-03-16 18:57 ` Arnd Bergmann
2021-02-17 10:21 ` Miklos Szeredi
2021-03-01 12:26 ` Alessio Balsini
2021-03-16 18:53 ` Arnd Bergmann
2021-03-18 16:13 ` Alessio Balsini
2021-03-18 21:15 ` Arnd Bergmann
2021-03-19 15:21 ` Alessio Balsini
2021-01-25 15:30 ` [PATCH RESEND V12 3/8] fuse: Definitions and ioctl for passthrough Alessio Balsini
2021-02-17 13:41 ` Miklos Szeredi
2021-02-19 7:05 ` Peng Tao
2021-02-19 8:40 ` Miklos Szeredi
2021-03-01 17:05 ` Alessio Balsini [this message]
2021-01-25 15:30 ` [PATCH RESEND V12 4/8] fuse: Passthrough initialization and release Alessio Balsini
2021-02-17 13:52 ` Miklos Szeredi
2021-05-05 12:21 ` Amir Goldstein
2021-05-17 11:36 ` Alessio Balsini
2021-05-17 13:21 ` Amir Goldstein
2021-01-25 15:30 ` [PATCH RESEND V12 5/8] fuse: Introduce synchronous read and write for passthrough Alessio Balsini
2021-02-17 14:00 ` Miklos Szeredi
2021-01-25 15:30 ` [PATCH RESEND V12 6/8] fuse: Handle asynchronous read and write in passthrough Alessio Balsini
2021-01-25 15:30 ` [PATCH RESEND V12 7/8] fuse: Use daemon creds in passthrough mode Alessio Balsini
2021-02-05 9:23 ` Peng Tao
2021-02-05 11:21 ` Alessio Balsini
2021-01-25 15:30 ` [PATCH RESEND V12 8/8] fuse: Introduce passthrough for mmap Alessio Balsini
2021-02-17 14:05 ` Miklos Szeredi
2021-04-01 11:24 ` Alessio Balsini
2021-11-18 18:31 ` [PATCH RESEND V12 0/8] fuse: Add support for passthrough read/write Amir Goldstein
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