A useful VFS change ...

Richard Sharpe realrichardsharpe at gmail.com
Wed Feb 26 11:32:13 MST 2014

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.

Richard Sharpe

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