On Thu, Jun 10, 2010 at 06:11:40PM +0100, Gordan Bobic wrote: > Is there a feature in btrfs to manually/explicitly mark hard-links > to be copy-on-write? My understanding is that this is what happens > when a snapshot is mounted rw and files modified. > > Consider this scenario: > > I have a base template fs. I make two snapshots of it that are > identical. The files in the template and both snapshots are > hard-links and have the same inode number. > > I change a file in one of the snapshots, and it gets copied on > write. I make the same change in the other snapshot, and that, too, > gets copied on write. I now have two identical files that are not > hard-links any more. > > What happens if I remove one of those files and create a hard-link > to the file in the other snapshot?
I'm afraid you can't do this. hard linking between subvolumes isn't allowed. But, what you can do is use the clone ioctl to make a new inode that references all of the data extents of an existing file, which would be a kind of COW hard link. Checkout bcp from btrfs-progs or cp --reflink from the latest..well wherever cp comes from. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
