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    SubjectRe: [PATCH v7 0/5] Introduce provisioning primitives
    On Wed, Jun 07 2023 at  7:27P -0400,
    Mike Snitzer <snitzer@kernel.org> wrote:

    > On Mon, Jun 05 2023 at 5:14P -0400,
    > Sarthak Kukreti <sarthakkukreti@chromium.org> wrote:
    >
    > > On Sat, Jun 3, 2023 at 8:57 AM Mike Snitzer <snitzer@kernel.org> 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

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