Re: [fuse-devel] [fuse] getattr() results ignored when writeback cache is active

[Nikolaus Rath <Nikolaus@rath.org>]

On Sep 21 2017, Maxim Patlasov <mpatlasov@virtuozzo.com> wrote:
> Oh, I understand now. Your example actually demonstrates that
> FUSE_WRITEBACK_CACHE must not be used if it's possible to modify
> underlying data (/tmp/issue_93/file_1) externally w.r.t fuse
> filesystem. That's correct. But initial statement:
>
>> this mode of operation is not suitable for any network filesystem 
>> even if no write operations are actually carried out
>
> is not, because it's not impossible to protect underlying data against
> such an external change somehow. A network filesystem is not obliged
> to keep transparent correspondence like /tmp/issue_93_mnt/file_1 <--> 
> /tmp/issue_93/file_1. It can keep all user data (and metadata) in
> internal structures making any external modifications
> impossible. Then, implementing exclusive write semantics would make
> using FUSE_WRITEBACK_CACHE safe. Agree?

I agree with what you're saying, but I don't agree that this should go
into the documentation for which the sentence in dispute was intended
:-). I think in 93% of all cases, the simplified statement will be more
helpful to a potential FUSE user than the correct one.

If this bothers you a lot, can we compromise and just be a little more
vague overall? I.e.,

| This mode of operation is therefore generally not suitable for
| filesystems where modifications may not come through the (local) FUSE
| layer (i.e, most network filesystems).


Best,
-Nikolaus

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