Re: JFFS2 determine writing state

["Jörn Engel" <joern@logfs.org>]

On Tue, 15 January 2008 21:51:44 +0000, Jamie Lokier wrote:
> Jörn Engel wrote:
> > 
> > I don't think there is a really good equivalent.  Writes happen
> > immediatly, but the changes may not become effective immediatly.  In a
> > way, the worst of both worlds. :)
> 
> I'm not sure if I understand what you mean by that.  Let me guess:
> 
> Do you mean that MTD write operations are started by write(), but
> write() returns before the writes are committed reliably?

Yes.  Write() may return before or after reliable commit, depending on
hardware, config options and sheer luck.

> If so does fsync/fdatasync/sync_page_range ensure that the preceding
> writes are committed reliably?

Yes.

> And does that include fsync on a
> directory following an atomic rename (for reliable replacement of a
> file)?

Yes.

> I guess write caching is an interesting beast for such a structured
> filesystem.  It would seem like a good opportunity to coalesce some
> tree node updates, something applications can't do themselves.

That bit is actually done already, modulo some bugs.  Once those bugs
are sorted out, caching actual data is a straight-forward extention.

Jörn

-- 
The wise man seeks everything in himself; the ignorant man tries to get
everything from somebody else.
-- unknown