Chris Mason wrote: > The main difference from data=ordered is that data=guarded only updates > the on disk i_size after all of the data blocks are on disk. This allows > us to avoid flushing all the data pages down to disk with every commit. I'm a bit confused, because I thought that was already guaranteed by ext3 data=ordered, due to the following mail: Date: Thu, 16 Mar 2006 13:09:04 -0500 Subject: Re: ext3_ordered_writepage() questions From: Theodore Ts'o <tytso@xxxxxxx> > >Yup. Ordered-mode JBD commit needs to write and wait upon all dirty > >file-data buffers prior to journalling the metadata. If we didn't run > >journal_dirty_data_fn() against those buffers then they'd still be under > >I/O after commit had completed. > > > In non-block allocation case, what metadata are we journaling in > writepage() ? > block allocation happend in prepare_write() and commit_write() > journaled the transaction. All the meta data updates should be done > there. What JBD commit are you refering to here ? Basically, this boils down to what is our definition of ordered-mode? If the goal is to make sure we avoid the security exposure of allocating a block and then crashing before we write the data block, potentially exposing previously written data that might be belong to another user, then what Badari is suggesting would avoid this particular problem. However, if what we are doing is overwriting our own data with more an updated, more recent version of the data block, do we guarantee that any ordering semantics apply? For example, what if we write a data block, and then follow it up with some kind of metadata update (say we touch atime, or add an extended attribute). Do we guarantee that if the metadata update is committed, that the data block will have made it to disk as well? Today that is the way things work, but is that guarantee part of the contract of ordered-mode? - Ted -- Jamie -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
