"Dr. David Alan Gilbert (git)" <dgilb...@redhat.com> wrote: > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com> > > Clarify that the pre_load function in a subsection is only called if > the subsection is found; to handle a missing subsection you may > set values in the pre_load of the parent vmsd. > > Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
Reviewed-by: Juan Quintela <quint...@redhat.com> > --- > docs/devel/migration.rst | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/docs/devel/migration.rst b/docs/devel/migration.rst > index 6ed3fce061..687570754d 100644 > --- a/docs/devel/migration.rst > +++ b/docs/devel/migration.rst > @@ -240,10 +240,13 @@ should succeed even with the data missing. To support > this the > subsection can be connected to a device property and from there > to a versioned machine type. > > -One important note is that the post_load() function is called "after" > -loading all subsections, because a newer subsection could change same > -value that it uses. A flag, and the combination of pre_load and post_load > -can be used to detect whether a subsection was loaded, and to > +The 'pre_load' and 'post_load' functions on subsections are only > +called if the subsection is loaded. > + > +One important note is that the outer post_load() function is called "after" > +loading all subsections, because a newer subsection could change the same > +value that it uses. A flag, and the combination of outer pre_load and > +post_load can be used to detect whether a subsection was loaded, and to > fall back on default behaviour when the subsection isn't present. > > Example: > @@ -315,8 +318,8 @@ For example: > the property to false. > c) Add a static bool support_foo function that tests the property. > d) Add a subsection with a .needed set to the support_foo function > - e) (potentially) Add a pre_load that sets up a default value for 'foo' > - to be used if the subsection isn't loaded. > + e) (potentially) Add an outer pre_load that sets up a default value > + for 'foo' to be used if the subsection isn't loaded. > > Now that subsection will not be generated when using an older > machine type and the migration stream will be accepted by older
