A useful VFS change ...

[Richard Sharpe]

On Wed, Feb 26, 2014 at 10:36 AM, Jeremy Allison <jra at samba.org> wrote:
> On Wed, Feb 26, 2014 at 10:32:13AM -0800, Richard Sharpe wrote:
>> On Wed, Feb 26, 2014 at 10:30 AM, Jeremy Allison <jra at samba.org> wrote:
>> > On Wed, Feb 26, 2014 at 10:28:37AM -0800, Richard Sharpe wrote:
>> >> Hi folks,
>> >>
>> >> In discussions with Dustin an idea was proposed for a way to make VFS
>> >> writing easier for those who are accessing user-space file systems (of
>> >> which we are seeing more and more these days.)
>> >>
>> >> One of the problems is that a user-space file system cannot, in
>> >> general, fall through to vfs_defaults, because, except in limited
>> >> cases, these call into the kernel via syscalls with FDs that make no
>> >> sense to the kernel.
>> >>
>> >> This requires that the VFS write write code for every VFS function
>> >> with many of them simply returning ENOTSUP.
>> >>
>> >> By adding a set of flags to the structure we could simplify things.
>> >> Perhaps we should go back to the old idea of OPAQUE vs TRANSPARENT VFS
>> >> modules. The default is TRANSPARENT, but if the writer sets the OPAQUE
>> >> bit, the infrastructure will return ENOTSUP if a call is made to a VFS
>> >> function that is not implemented.
>> >
>> > Rather than complicating the structure, shouldn't we
>> > just create a new 'defaults' module that always returns
>> > ENOTSUP for every call, that OEMs can then stack their
>> > user-space filesystem modules on top of ?
>>
>> That would do the job as well.
>
> Might be a bit easier, we just copy the skel_opaque.c
> module and change the returns..

Indeed, but we also have to make waf work correctly for the
examples/VFS directory as well :-)

-- 
Regards,
Richard Sharpe
(何以解憂？唯有杜康。--曹操)