Re: [RFC PATCH v1 04/25] hw/xen: Implement XenStore transactions

[Paul Durrant <xadimgnik@xxxxxxxxx>]

On 02/03/2023 15:34, David Woodhouse wrote:
> From: David Woodhouse <dwmw@xxxxxxxxxxxx>
>
> Given that the whole thing supported copy on write from the beginning,
> transactions end up being fairly simple. On starting a transaction, just
> take a ref of the existing root; swap it back in on a successful commit.
>
> The main tree has a transaction ID too, and we keep a record of the last
> transaction ID given out. if the main tree is ever modified when it isn't
> the latest, it gets a new transaction ID.
>
> A commit can only succeed if the main tree hasn't moved on since it was
> forked. Strictly speaking, the XenStore protocol allows a transaction to
> succeed as long as nothing *it* read or wrote has changed in the interim,
> but no implementations do that; *any* change is sufficient to abort a
> transaction.
>
> This does not yet fire watches on the changed nodes on a commit. That bit
> is more fun and will come in a follow-on commit.
>
> Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> ---
>   hw/i386/kvm/xenstore_impl.c | 150 ++++++++++++++++++++++++++++++++++--
>   tests/unit/test-xs-node.c   | 118 ++++++++++++++++++++++++++++
>   2 files changed, 262 insertions(+), 6 deletions(-)
Reviewed-by: Paul Durrant <paul@xxxxxxx>