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



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@xxxxxxxx>
---
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




 


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