Hi Juergen,
On 28/07/2023 07:23, Juergen Gross wrote:
On 27.07.23 23:53, Julien Grall wrote:
Hi Juergen,
On 24/07/2023 12:02, Juergen Gross wrote:
Struct xs_tdb_record_hdr is used for nodes stored in the data base.
When working on a node, struct node is being used, which is including
the same information as struct xs_tdb_record_hdr, but in a different
format. Rework struct xs_tdb_record_hdr in order to prepare including
it in struct node.
Do the following modifications:
- move its definition to xenstored_core.h, as the reason to put it into
utils.h are no longer existing
- rename it to struct node_hdr, as the "tdb" in its name has only
historical reasons
- replace the empty permission array at the end with a comment about
the layout of data in the data base (concatenation of header,
permissions, node contents, and children list)
- use narrower types for num_perms and datalen, as those are naturally
limited to XENSTORE_PAYLOAD_MAX (childlen is different here, as it is
in theory basically unlimited)
The assumption is XENSTORE_PAYLOAD_MAX will never change and/or always
apply for all the connection. I am aware of at least one downstream
use where this is not the case.
I am happy to use narrower types, but I would at least like some
checks in Xenstore to ensure the limits are not reached.
I will add a BUILD_BUG_ON().
Initially I was thinking about a runtime check, but I am also fine with
a BUILD_BUG_ON() if it is right next to length check in handle_input().
So if someone decided to add different payload size depending on the
domain (such as privileged domain could do more), it would be easier to
spot what else needs to be changed.
OOI, do you have a use case where a node would be shared with more
than 255 domains?
No, but limiting it wouldn't give any real advantage.
I guess by advantage you mean that the size of the structure would still
be the same. I thought this was the rationale but I asked just in case
you had something else in mind. For instance, Xen technically supports
up to ~32 000 domains. But I think it would be crazy to decide to have
more than a few tens permissions on a node :).
Cheers,
--
Julien Grall
