On Thu, Dec 25, 2008 at 10:37:36PM -0500, Theodore Tso wrote: > On Thu, Dec 25, 2008 at 10:00:05PM -0200, Alberto Bertogli wrote: > > > > I think I'm not explaining myself correctly. My code has _nothing_ to do > > with ext2/3/4 (or any other filesystem) whatsoever. I'm not using the > > journal as an external one for a filesystem. I want to use it to be able > > to do atomic writes in my own, filesystem independant, device-mapper > > code. > > How many block writes are you batching into a single transaction? If > you're not careful you may find that performance overhead will be > quite expensive. At this moment I'm trying to keep it simple, so I plan to batch two for each sector written to the device: one for the metadata and one for the data. > > After what you told me (both this and the deprecation of > > jbd2_journal_create()), I took a look at e2fsprogs' source. From what I > > could see, "mke2fs -O journal_dev" creates the external journal inside > > some ext2/3/4 structures, which caused my journal-loading code to fail > > (because it doesn't know about ext stuff). > > Yes, this is necessary because in a production system you need to be > able to identify the external journal by UUID, and the ext2/3/4 > superblock makes it easy to add a label, UUID, et. al. It also > significantly lowers the chance that an external journal will get > misidentified as some other filesystem based on the data stored in the > journal. Yes, it makes sense. I've reserved the first sector for that purpose. Thanks a lot, Alberto -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
