Excerpts from liubo's message of 2011-02-24 04:40:55 -0500: > > Data compression and data cow are controlled across the entire FS by mount > options right now. ioctls are needed to set this on a per file or per > directory basis. This has been proposed previously, but VFS developers > wanted us to use generic ioctls rather than btrfs-specific ones. > > We need to fit these into the existing per-inode flags, and to use the generic > FS_IOCTL_SETFLAGS ioctl. For data compression, there are the existing > compression flags of vfs inode, while for datacow, there is no flag to > indicate it, which we need to add. > So, what we will do is to add datacow flag in vfs inode flags and then to > set or to unset btrfs compress/cow flag on the corresponding btrfs inode's flag > per file or per directory. Moreover, we also add a compression type ioctl to > make this feature more flexible. > > I really expect some advices and comments on the followings: > > - In this patch, I made a special ioctl to set compress type, and to record > the compress_type per inode on disk, I've consumed some reserved space of > btrfs_inode_item, so is this acceptable? I don't expect people to mix compression types on the disk. There really should just be one true compression method (probably LZO once it has been established for a while). So, I'd prefer that we store this in the super, and just have flags in the inode for enabling or disabling compression. > Meanwhile, I got another idea from my collegue, could we just owe the whole > compress type thing to new proper mount options, ie, > mount xxx xxx -o compress=a,inode_compress=b? > Seems that this makes mount more flexible. It does make it more flexible, but I think sometimes extra flexibility leads to more QA time and isn't often used by the actual users ;) > > - When we are inclined to set inode's compression type, should it be a "force" > mode? > This is much like the difference between mount as compress and mount as > compress-force. I'd store this as flags in the super too. > > - For directory basis, after compress/cow ioctl on it, any files that are > created or renamed in it, or moved into it, will inherit the directory's > compress and datacow attribute. > Here comes to some disputes, is it right that renamed and moved files > also inherit the father directory's compress & datacow attribute? > And if what we are dealing with is directory, should this behaviour be > recursive or not? > I'm inclined to leave these recursive things to btrfs-progs if this is > necessary. I'd say that if we rename a file into a directory it does inherit, but not make it recursive. -chris -- 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
