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_vfs.c
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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