On Tue, Oct 24, 2006 at 11:59:28PM +1000, David Chinner wrote: > That's the wrong way to look at it. if you want the userspace > process to specify a location, then you should preallocate it first > before doing anything else. There is no need to clutter a simple > data mover interface with all sorts of unnecessary error handling. This is doable, but it adds a huge amount of complexity before we could implement on-line defragmentation. First of all, we would need a way of allowing userpsace to specify which blocks should be used in the preallocation. Secondly, we would need a way of marking blocks as "preallocated but not pre-zeroed"; otherwise we would have to zero out all of the blocks in order to assure security (don't want userspace programs seeing the previous contents of the data blocks), only to do the copy and the extents vector swap. That's a huge amount of work, and while the above two features can be useful for other things, it's not clear it's worth it to require this as the only way to implement on-line defragging. You're right that it's a way of making things be more generic, but it means that each filesystem needs to have a huge amount of additional complexity and potential filesystem format changes before they could take advantage of this general framework. (For example, you'd never be able to do this with the FAT filesystem, or the ext2 or ext3 filesystems; it would work for ext4 only *after* we implement the above mentioned new features and the associated filesystem format changes.) Regards, - Ted - 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
