On Mon, 2011-01-03 at 16:21 +0200, Benny Halevy wrote: > On 2010-12-17 01:07, Christoph Hellwig wrote: > > On Thu, Dec 16, 2010 at 11:21:21AM -0500, Matt W. Benjamin wrote: > >> Hi, > >> > >> We have a files implementation which wants to receive LAYOUTCOMMIT when a client is finished with a layout. It was my clear understanding from rfc5661 that we could expect this behavior. > > > > Care to post it to the list? > > > > I don't know what Matt's server is doing but the fundamental problem is > manifested with extending a file with parallel DS writes. > Assuming that the DS writes are executed in arbitrary order, > exposing the file length before LAYOUTCOMMIT can cause > a concurrent reader to read a hole. Although locking can > solve this case, day-to-day applications that work well over > local filesystem and legacy NFS may break because of this. ...and this differs from ordinary NFS writes exactly how? Both cached and uncached (i.e. O_DIRECT) writes can and will be flushed to disk in entirely random order when writing to the MDS. If you have a parallel reader on another client (or even on the same client in the case of O_DIRECT), and want it to see accurate data, then use locking. If not, you will see holes and other strangeness. IOW: There are no 'day-to-day applications that work well over legacy NFS' that rely on this behaviour. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
