Re: [PATCH RESEND V11 0/7] fuse: Add support for passthrough read/write

[wu-yan@xxxxxxx]

On 1/22/21 7:06 PM, Alessio Balsini wrote:
> On Tue, Jan 19, 2021 at 12:34:23PM +0000, Alessio Balsini wrote:
> > On Tue, Jan 19, 2021 at 07:06:54PM +0800, Rokudo Yan wrote:
> > > on Mon, Jan 18, 2021 at 5:27 PM Alessio Balsini <balsini@xxxxxxxxxxx> wrote:
> > > > This is the 11th version of the series, rebased on top of v5.11-rc4.
> > > > Please find the changelog at the bottom of this cover letter.
> > > >
> > > > Add support for file system passthrough read/write of files when enabled
> > > > in userspace through the option FUSE_PASSTHROUGH.
> > > [...]
> > >
> > >
> > > Hi Allesio,
> > >
> > > Could you please add support for passthrough mmap too ?
> > > If the fuse file opened with passthrough actived, and then map (shared) to (another) process
> > > address space using mmap interface. As access the file with mmap will pass the vfs cache of fuse,
> > > but access the file with read/write will bypass the vfs cache of fuse, this may cause inconsistency.
> > > eg. the reader read the fuse file with mmap() and the writer modify the file with write(), the reader
> > > may not see the modification immediately since the writer bypass the vfs cache of fuse.
> > > Actually we have already meet an issue caused by the inconsistency after applying fuse passthrough
> > > scheme to our product.
> > >
> > > Thanks,
> > > yanwu.
> >
> > Hi yanwu,
> >
> > Thank you for your interest in this change.
> >
> > FUSE passthrough for mmap is an extension that is already in my TODO
> > list, together with passthrough for directories.
> > For now I would prefer to keep this series minimal to make the review
> > process leaner and simpler.
> > I will start working on extending this series with new features and
> > addressing more corner cases as soon as these changes get merged, what
> > do you think?
> >
> > Thanks,
> > Alessio
>
> Hi yanwu,
>
> Sorry if I overlooked this issue. I added memory-mapping to my tests and
> could reproduce/verify this wrong behavior you mentioned.
>
> I created this WIP (history may change) branch that has the missing mmap
> implementation:
>
>    https://github.com/balsini/linux/commits/fuse-passthrough-v12-develop-v5.11-rc4
>
> I did some mmap testing in the last days with this extra mmap
> implementation and couldn't find any issues, everything seems to be
> working as expected with the extra mmap patch. Can you please confirm
> this is fixed on your end too?
> I'm also going to revert in this branch the stacking policy changes to
> how they were in V10 as suggested by Amir if there are no concerns with
> that.
> I'm waiting for some extra tests to complete and, if no issue is
> detected, I'll post the V12 series super soon.
>
> Thanks,
> Alessio

Hi, Alessio

Thank you for your reply. I have already added mmap for passthrough in 
our product, and the issue mentioned before is fixed. And I will update 
if any new issuses found.

Thanks
yanwu