[PATCH 00/33] migration: capture error reports into Error object

[Daniel P . Berrangé]

Due to its long term heritage most of the migration code just invokes
'error_report' when problems hit. This was fine for HMP, since the
messages get redirected from stderr, into the HMP console. It is not
OK for QMP because the errors will not be fed back to the QMP client.

This wasn't a terrible real world problem with QMP so far because
live migration happens in the background, so at least on the target side
there is not a QMP command that needs to capture the incoming migration.
It is a problem on the source side but it doesn't hit frequently as the
source side has fewer failure scenarios. None the less on both sides it
would be desirable if 'query-migrate' can report errors correctly.
With the introduction of the load-snapshot QMP commands, the need for
error reporting becomes more pressing.

Wiring up good error reporting is a large and difficult job, which
this series does NOT complete. The focus here has been on converting
all methods in savevm.c which have an 'int' return value capable of
reporting errors. This covers most of the infrastructure for controlling
the migration state serialization / protocol.

The remaining part that is missing error reporting are the callbacks in
the VMStateDescription struct which can return failure codes, but have
no "Error **errp" parameter. Thinking about how this might be dealt with
in future, a big bang conversion is likely non-viable. We'll probably
want to introduce a duplicate set of callbacks with the "Error **errp"
parameter and convert impls in batches, eventually removing the
original callbacks. I don't intend todo that myself in the immediate
future.

IOW, this patch series probably solves 50% of the problem, but we
still do need the rest to get ideal error reporting.

In doing this savevm conversion I noticed a bunch of places which
see and then ignore errors. I only fixed one or two of them which
were clearly dubious. Other places in savevm.c where it seemed it
was probably ok to ignore errors, I've left using error_report()
on the basis that those are really warnings. Perhaps they could
be changed to warn_report() instead.

There are alot of patches here, but I felt it was easier to review
for correctness if I converted 1 function at a time. The series
does not neccessarily have to be reviewed/appied in 1 go.

Daniel P. Berrangé (33):
  migration: push Error **errp into qemu_loadvm_state()
  migration: push Error **errp into qemu_loadvm_state_header()
  migration: push Error **errp into qemu_loadvm_state_setup()
  migration: push Error **errp into qemu_load_device_state()
  migration: push Error **errp into qemu_loadvm_state_main()
  migration: push Error **errp into qemu_loadvm_section_start_full()
  migration: push Error **errp into qemu_loadvm_section_part_end()
  migration: push Error **errp into loadvm_process_command()
  migration: push Error **errp into loadvm_handle_cmd_packaged()
  migration: push Error **errp into loadvm_postcopy_handle_advise()
  migration: push Error **errp into ram_postcopy_incoming_init()
  migration: push Error **errp into loadvm_postcopy_handle_listen()
  migration: push Error **errp into loadvm_postcopy_handle_run()
  migration: push Error **errp into loadvm_postcopy_ram_handle_discard()
  migration: make loadvm_postcopy_handle_resume() void
  migration: push Error **errp into loadvm_handle_recv_bitmap()
  migration: push Error **errp into loadvm_process_enable_colo()
  migration: push Error **errp into colo_init_ram_cache()
  migration: push Error **errp into check_section_footer()
  migration: push Error **errp into global_state_store()
  migration: remove error reporting from qemu_fopen_bdrv() callers
  migration: push Error **errp into qemu_savevm_state_iterate()
  migration: simplify some error reporting in save_snapshot()
  migration: push Error **errp into qemu_savevm_state_setup()
  migration: push Error **errp into qemu_savevm_state_complete_precopy()
  migration: push Error **errp into
    qemu_savevm_state_complete_precopy_non_iterable()
  migration: push Error **errp into qemu_savevm_state_complete_precopy()
  migration: push Error **errp into qemu_savevm_send_packaged()
  migration: push Error **errp into qemu_savevm_live_state()
  migration: push Error **errp into qemu_save_device_state()
  migration: push Error **errp into qemu_savevm_state_resume_prepare()
  migration: push Error **errp into postcopy_resume_handshake()
  migration: push Error **errp into postcopy_do_resume()

 include/migration/colo.h                      |   2 +-
 include/migration/global_state.h              |   2 +-
 migration/colo.c                              |  12 +-
 migration/global_state.c                      |   6 +-
 migration/migration.c                         |  80 ++-
 migration/postcopy-ram.c                      |   8 +-
 migration/postcopy-ram.h                      |   2 +-
 migration/ram.c                               |  17 +-
 migration/ram.h                               |   4 +-
 migration/savevm.c                            | 594 ++++++++++--------
 migration/savevm.h                            |  23 +-
 .../tests/internal-snapshots-qapi.out         |   3 +-
 12 files changed, 427 insertions(+), 326 deletions(-)

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2.29.2