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Erik Larsson  
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 More options Jan 5 2010, 10:03 pm
From: Erik Larsson <eri...@kth.se>
Date: Wed, 06 Jan 2010 04:03:06 +0100
Local: Tues, Jan 5 2010 10:03 pm
Subject: Re: Some Answers
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Hi Thomas,

If you look in the XNU source code here:

http://www.opensource.apple.com/source/xnu/xnu-1486.2.11/bsd/vfs/kpi_...

Some way down in the source code you will find the following comment:
     /* Non-threadsafe filesystems are not supported for K64 */

So far MacFUSE has been able to get by just by not passing the
VFS_TBLTHREADSAFE flag in the file system capabilities (see fuse_vfsops.c).
This is not possible anymore in K64 (the kernel extension just won't
load if it's not thread safe).

I suppose Amit was planning to do an initial biglock approach for
MacFUSE (maybe one big lock for all the MacFUSE kernel extension code?),
but it's not implemented yet (the fuse_biglock_vnops.* files).

I'm not 100% sure of the implications, but I could think of trying out
an approach with a big mutex protecting all the vnops (and vfsops?).
Let me know if you want to cooperate on solving this.

Regards,

- Erik

Tomas Carnecky wrote 2010-01-05 18.15:

> Do you at least know what needs to be changed or are you completely in
> the dark as to which changes there have been in Snow Leopard which make
> the 64bit MacFUSE kext incompatible?

> If you know that you don't have time to work on MacFUSE maybe you should
> make an announcement to the group that you are looking for someone to
> take over the project. I don't think anybody is going to rush to work on
> it given the uncertainty whether you will pick it up in the future or not.

> I'd probably work on MacFUSE as far as I can. But where do I start? What
> needs to be done in the MacFUSE kext? What was that
> fuse_biglock_vnode_operation_entries about? Why does the 64bit kernel
> need locking where the 32bit kernel doesn't? Did you plan to use
> something like the Linux Big Kernel Lock (BKL, basically a single lock
> for the whole kernel)? Or which data structures need to be protected
> from concurrent access?
> I see the current source has 'XXX: Locking' comments in a few places
> throughout the vnops code. Does that mean that the current vnops code
> doesn't use any locks? Is that safe in 32bit kernels?

> tom


 
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