Re: Question regarding concurrent accesses through block device and fs

[Nick Piggin <nickpiggin@yahoo.com.au>]

On Thursday 12 March 2009 20:00:38 Francis Moreau wrote:
> On Thu, Mar 12, 2009 at 9:22 AM, Nick Piggin <nickpiggin@yahoo.com.au> 
wrote:
> > Ignore details like crashes, direct IO and coherency between data
> > mappings and buffercache where things get a bit hairy, and it's just a
> > writeback cache. The last thing you write to some location will be what
> > you get back if you read from that location -- regardless of whether it
> > is dirty or clean or not present when you ask for it (and has to be read
> > from disk).
>
> Well yes but I was wondering in the special where the kernel crash or
> the power supply is down how the kernel is minimizing the risk of file
> system inconsistency. Hence my questions about metadata handling.

Well, journalling filesystems, other filesystems can do synchronous
metadata updates (write through) which can help too. There is really
nothing that the generic pagecache/buffercache code does to try to
handle this because it is far to filesystem specific.