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

[Jürgen Groß <jgross@xxxxxxxx>]

On 11.03.25 10:43, Julien Grall wrote:
> 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?
Good catch.

I think I need to change this to be a flag indicating that the unique-id
is present and located at the next 8-byte boundary after "data".


Juergen

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