[RFC,0/1] migration: Update error description whenever migration fails

Message

Tejus GK May 3, 2023, 8:31 p.m. UTC

Hi everyone,

Currently, in QEMU, whenever a migration fails, its state is set to
MIGRATION_STATUS_FAILED
via the function migrate_set_state. However, there are places in the
code where the migration is marked as a failed migration; however, the
error description is never updated in the migration state object. This
causes problems when libvirt tries to query for the status of the
migration via a query-migrate; it never receives an error description
and hence reports the error as "unexpectedly failed". This
doesn't give us any information about what actually went wrong with
the migration.

An approach to solve this problem, which this patch explores, is to
update the migration errors through  migrate_set_error, whenever the
migration state is updated to MIGRATION_STATUS_FAILED. However,
sometimes these error descriptions can be due to various reasons or be
too vague.

An alternative approach to tackle this is to update the error
description from the point where the error actually occurred. For
instance, an error which occurs while saving the vmstate in the function
vmstate_save_state_v in the file migration/vmstate.c, results in a
failed migration, hence the error description can be updated here
itself, rather than updating it in the function migration_completion,
present in migration/migration.c.

tejus.gk (1):
  migration: Update error description whenever migration fails

 migration/migration.c | 8 ++++++++
 1 file changed, 8 insertions(+)