On Fri, 30 Jul 2021, Al Viro wrote: > On Wed, Jul 28, 2021 at 05:30:04PM -0400, Josef Bacik wrote: > > > I don't think anybody has that many file systems. For btrfs it's a single > > file system. Think of syncfs, it's going to walk through all of the super > > blocks on the system calling ->sync_fs on each subvol superblock. Now this > > isn't a huge deal, we could just have some flag that says "I'm not real" or > > even just have anonymous superblocks that don't get added to the global > > super_blocks list, and that would address my main pain points. > > Umm... Aren't the snapshots read-only by definition? No, though they can be. subvols can be created empty, or duplicated from an existing subvol. Any subvol can be written, using copy-on-write of course. NeilBrown
