Re: [PATCH v8 7/9] docs: update xenstore migration stream definition

[Julien Grall <julien@xen.org>]

Hi Juergen,

On 04/02/2025 11:34, Juergen Gross wrote:
> In order to close a race window for Xenstore live update when using
> the new unique_id of domains, the migration stream needs to contain
> this unique_id for each domain known by Xenstore.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
> V8:
> - new patch
> ---
>   docs/designs/xenstore-migration.md | 14 +++++++++++++-
>   1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/designs/xenstore-migration.md b/docs/designs/xenstore-migration.md
> index 082314bf72..fba691ee0d 100644
> --- a/docs/designs/xenstore-migration.md
> +++ b/docs/designs/xenstore-migration.md
> @@ -156,7 +156,7 @@ the domain being migrated.
>   ```
>       0       1       2       3       4       5       6       7    octet
>   +-------+-------+-------+-------+-------+-------+-------+-------+
> -| conn-id                       | conn-type     |               |
> +| conn-id                       | conn-type     | uniq-id-off   |
>   +-------------------------------+---------------+---------------+
 >   | conn-spec>   ...
> @@ -165,6 +165,9 @@ the domain being migrated.
>   +---------------+---------------+-------------------------------+
>   | data
>   ...
> ++---------------------------------------------------------------+
> +| unique-id                                                     |
> ++---------------------------------------------------------------+
>   ```
>   
>   
> @@ -178,6 +181,12 @@ the domain being migrated.
>   |                | 0x0001: socket                               |
>   |                | 0x0002 - 0xFFFF: reserved for future use     |
>   |                |                                              |
> +| `uniq-id-off`  | The offset (in octets) of the `unique-id`    |
> +|                | field from the start of the record body.     |
> +|                | If 0, no `unique-id` field is present.       |
> +|                | Only needed for `shared ring` connection in  |
> +|                | live update streams.                         |
> +|                |                                              |

Looking at the rest of the record, the unique ID would be past the 
in-data (length is 2-byte) and the out-data (length is 4-byte). So 
technically the offset would need 5-bytes. But here you are using 
2-bytes. Can you explain why?

Cheers,

-- 
Julien Grall