On Thu, Jun 02, 2016 at 06:58:33PM -0700, Darrick J. Wong wrote: > On Fri, Jun 03, 2016 at 08:54:15AM +1000, Dave Chinner wrote: > > On Thu, Jun 02, 2016 at 04:19:07PM +0200, Christoph Hellwig wrote: > > > I've had some vocal user requests to allow enabling reflinks at run time, > > > which happens to be a mostly trivial feature. The only caveat is that we > > > need a large enough log size to support the reflink requirements, but for > > > typical large file systems that's not an issue. > > > > Hmmm - how does this interact with all the rmap code? I was not > > planning on enabling reflink without rmap and vice versa simply > > because it makes the validation and testing matrix vastly more > > complex. Indeed, having reflink turned on after a filesystem has > > aged for some time (i.e. from unknown initial conditions) makes > > validation especially tricky.... > > Well... > > It's not strictly impossible, but there will be some problems running > repair and remounting. > > The patchset doesn't actually check that we satisfy the minimum log > space requirement, which will result in xfs refusing to mount. As > Christoph says, this is only an issue on small FSes, but nevertheless, > we shouldn't trap the user like that. xfs_log_mount always verified the required log size. > Second, mkfs lays out all the AG btree roots at the start of the AG > before finding an aligned inode block for the root inode. xfs_repair > feeds the same algorithm from the on-disk feature fields to check that > s_rootino is sane, and gets very unhappy if it doesn't find the root > inode at the computed location. Adding the two btree root blocks is > enough to shift the root inode from 96 to 128. This all can be fixed, > but it /was/ convenient not to have to support weirdo upgraded XFSes > like ext4. :) Yes, that algorithm might be unhappy, but I don't think it's overly smart to rely on it either. > Furthermore, if you turn on reflink, you should enable the per-AG > reservations so we don't crash the FS by running out of space when it > needs a block for the refcountbt. xfs_refcountbt_calc_reserves is switched to use xfs_mp_hasreflink, so it will do the right thing. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
