[ceph-users] deprecating inline_data support for CephFS

A couple of weeks ago, I sent a request to the mailing list asking whether anyone was using the inline_data support in cephfs: https://docs.ceph.com/docs/mimic/cephfs/experimental-features/#inline-data I got exactly zero responses, so I'm going to formally propose that we move to start deprecating this feature for Octopus. Why deprecate this feature? =========================== While the userland clients have support for both reading and writing, the kernel only has support for reading, and aggressively uninlines everything as soon as it needs to do any writing. That uninlining has some rather nasty potential race conditions too that could cause data corruption. We could work to fix this, and maybe add write support for the kernel, but it adds a lot of complexity to the read and write codepaths in the clients, which are already pretty complex. Given that there isn't a lot of interest in this feature, I think we ought to just pull the plug on it. How should we do this? ====================== We should start by disabling this feature in master for Octopus. In particular, we should stop allowing users to call "fs set inline_data true" on filesystems where it's disabled, and maybe throw a loud warning about the feature being deprecated if the mds is started on a filesystem that has it enabled. We could also consider creating a utility to crawl an existing filesystem and uninline anything there, if there was need for it. Then, in a few release cycles, once we're past the point where someone can upgrade directly from Nautilus (release Q or R?) we'd rip out support for this feature entirely. Thoughts, comments, questions welcome. -- Jeff Layton <jlayton(a)redhat.com>