linux-kernel - Re: [fuse-devel] Changes in 4.7.

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Message-ID: <CAJfpegveErYS8+23eNejT8K9Gimtw9w2kXRpyqhqQVSwCFBHgg@mail.gmail.com>
Date:	Tue, 31 May 2016 09:17:56 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Stef Bon <stefbon@...il.com>
Cc:	"fuse-devel@...ts.sourceforge.net" <fuse-devel@...ts.sourceforge.net>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [fuse-devel] Changes in 4.7.

On Tue, May 31, 2016 at 9:08 AM, Stef Bon <stefbon@...il.com> wrote:
> Hi,
>
> I've read some news about the 4.7 kernel :
>
> "And in particular, if
> you're a low-level filesystem person, or involved in other ways in
> path component lookup (security layer etc), go check that everything
> looks ok, and if your filesystem isn't one that does parallel lookups
> or readdirs yet (because locking issues), take a look at that too."
>
> https://lkml.org/lkml/2016/5/29/77
>
> Does this have consequenses for fuse?
> I know that with some filesystems I've written the readdir call locks
> the directory exclusive.

The problem would be if the fuse filesystem assumed serialized
lookup/readdir and they don't do any locking themselves.

We probably need to conditionally re-add the lookup/readdir
serialization to the fuse kernel module, with an INIT flag to
explicitly enable parallel readdir and lookup (i.e. disable the
serialization).

Thanks,
Miklos