Re: invalidate the buffer heads of a block device

[Jan Kara <jack@suse.cz>]

On Tue 30-09-14 08:58:54, Thanos Makatos wrote:
> > > If the above observations are correct, it seems that I have to either
> > > extend BLKFLSBUF to some invalidate such memory maps (I'm completely
> > > ignorant in that field, is it even possible?), or look for other
> > > solutions.
> >   Well, you could unmap the pages of block device that are mapped in your
> > new ioctl but I don't think it's easily possible to disallow userspace to fault the
> > pages back behind your back. And that could be a problem for you.
> 
> I'm not sure I understand what "I don't think it's easily possible to
> disallow userspace to fault the pages back behind your back" means, could
> you explain?
  I mean by that that even if you evict page from page cache, it can be
immediately reloaded from the device. So you have to be careful to
provide new data once you decide to go and evict page cache. But that's
obvious I guess.

> I definitely don't care what happens to the process that dared to memory
> map the block device, this configuration is not supported in my
> environment. Is this what you mean?
  OK, so it isn't supported but you don't want such application to be able
to screw up your other processes, am I right?

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR