On Wed, Jun 07 2023 at 7:27P -0400, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > On Mon, Jun 05 2023 at 5:14P -0400, > Sarthak Kukreti <sarthakkukreti@xxxxxxxxxxxx> wrote: > > > On Sat, Jun 3, 2023 at 8:57 AM Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > > > > > > We all just need to focus on your proposal and Joe's dm-thin > > > reservation design... > > > > > > [Sarthak: FYI, this implies that it doesn't really make sense to add > > > dm-thinp support before Joe's design is implemented. Otherwise we'll > > > have 2 different responses to REQ_OP_PROVISION. The one that is > > > captured in your patchset isn't adequate to properly handle ensuring > > > upper layer (like XFS) can depend on the space being available across > > > snapshot boundaries.] > > > > > Ack. Would it be premature for the rest of the series to go through > > (REQ_OP_PROVISION + support for loop and non-dm-thinp device-mapper > > targets)? I'd like to start using this as a reference to suggest > > additions to the virtio-spec for virtio-blk support and start looking > > at what an ext4 implementation would look like. > > Please drop the dm-thin.c and dm-snap.c changes. dm-snap.c would need > more work to provide the type of guarantee XFS requires across > snapshot boundaries. I'm inclined to _not_ add dm-snap.c support > because it is best to just use dm-thin. > > And FYI even your dm-thin patch will be the starting point for the > dm-thin support (we'll keep attribution to you for all the code in a > separate patch). > > > Fair points, I certainly don't want to derail this conversation; I'd > > be happy to see this work merged sooner rather than later. > > Once those dm target changes are dropped I think the rest of the > series is fine to go upstream now. Feel free to post a v8. FYI, I've made my latest code available in this 'dm-6.5-provision-support' branch (based on 'dm-6.5'): https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-6.5-provision-support It's what v8 should be plus the 2 dm-thin patches (that I don't think should go upstream yet, but are theoretically useful for Dave and Joe). The "dm thin: complete interface for REQ_OP_PROVISION support" commit establishes all the dm-thin interface I think is needed. The FIXME in process_provision_bio() (and the patch header) cautions against upper layers like XFS using this dm-thinp support quite yet. Otherwise we'll have the issue where dm-thinp's REQ_OP_PROVISION support initially doesn't provide the guarantee that XFS needs across snapshots (which is: snapshots inherit all previous REQ_OP_PROVISION). Mike
