On Mon, 2009-03-16 at 11:28 -0400, jim owens wrote: > CSights wrote: > > Hi everyone, > > I'm curious what would happen in btrfs if the following commands were > > issued: > > > > # cp file1 file2 > > # chown newuser:newgroup file2 > > > > Where file1 was owned by olduser:oldgroup. > > > > > > If I understand copy-on-write correctly the "cp" would merely create a > > new > > pointer (or whatever it is called :( ) containing the files' metadata but > > the > > file contents would not actually be duplicated. > > NO. The concept you describe requires "deduplicate". > > What you are forgetting is that "cp" is a user-space program that > reads data and writes it to a new file. The kernel does not see > this as a Copy. >
This is true, cp makes a full copy of the file. The btrfs utilities include a program called bcp that makes a COW copy of a single file (or directory tree) with a btrfs specific ioctl. -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
