On 5/11/15 11:14 AM, Brian Foster wrote: > On Fri, May 08, 2015 at 03:48:16PM -0500, Eric Sandeen wrote: >> > This adds a new superblock field, sb_meta_uuid. If set, along with >> > a new incompat flag, the code will use that field on a V5 filesystem >> > to compare to metadata UUIDs, which allows us to change the user- >> > visible UUID at will. Userspace handles the setting or clearing >> > of the incompat flag as appropriate, as the UUID gets written. >> > >> > If the incompat flag is not set, copy the user-visible UUID into >> > into the meta_uuid slot in memory; this is not written back to disk in >> > this case. >> > >> > The remainder of this patch simply switches verifiers, initializers, >> > etc to use the new sb_meta_uuid field. >> > >> > Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx> >> > --- > This all looks fine to me. The only thing that confuses me is why we > continue to use sb_uuid for the log. Eric points out on irc that we > can't modify the uuid when the log is dirty, so we can't actually break > anything in this manner. In other words, we effectively already handle a > modified uuid with respect to the log. > > That said, it seems inconsistent to me to create a metadata uuid field > and not use it for all metadata. My expectation from such a change is to > see sb_uuid now used only for user facing bits (e.g., mount and get geo > related) and sb_meta_uuid used everywhere else. Instead, we use sb_uuid > for the user facing bits, sb_meta_uuid for the internal bits that can't > handle a uuid change and sb_uuid for the internal bits that can. > > I suppose I could be convinced otherwise if there's context I'm missing, > but otherwise this seems a bit confusing to me... > > Brian Yeah, I'm sympathetic to that argument. I can look into using sb_meta_uuid for the log too, if the incompat flag is set. I had skipped it just because that use of the UUID predated the CRC changes. -Eric _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
