[Qemu-devel] [PATCH 00/16] PCI device assignment: improve error reporting over QMP

[Laszlo Ersek <lersek@redhat.com>]

This is for <https://bugzilla.redhat.com/show_bug.cgi?id=616415>.

In general, we want to propagate non-fatal (ie. non-exit()ing,
non-abort()ing) errors to the QMP caller, rather than printing them
on-site. The series focuses on errors raised at PCI assignment time (ie.
reachable from assigned_initfn()), other errors are not converted.

Errors are not propagated through assigned_initfn(); let's wait for
someone else to convert "kvm-pci-assign" from qdev to QOM. The series is
nonetheless an improvement, because the forwarding of initialization
errors now stops just before device_realize(). We set the
stored/persistent monitor error there.

Informative and warning messages (that report about circumstances that
don't break the assignment operation) cannot terminate in
qerror_report_err(), because that would set the persistent monitor
error, breaking the high level (QMP) operation.

A call graph rooted in assigned_initfn() was generated with cflow.
Leaves that could never fail were removed from the graph (and this
property similarly propagated upwards as far as possible).

The patchset loosely follows a bottom-up algorithm on this calltree. Any
leaf that reports an error internally and returns a related failure is
converted to "throw" an Error structure instead. All direct callers of
the converted leaf are addressed at once, in the same patch, to consume
the error (and they become the new leaves gradually).

When the leaf to be converted is also called outside of
"hw/i386/kvm/pci-assign.c", the conversion keeps a compatibility
function under the original name, so that conversion of callers
unrelated to PCI assignment can be deferred.

Reviewers should copy the call graph to a text file, and mark, as the
series progresses, fully converted functions. (Ie. functions that now
report their terminating error messages with Error objects only.)

  assigned_initfn()
      error_report()
      get_real_device()
          monitor_handle_fd_param()
          error_report()
          get_real_vendor_id()
              get_real_id()
                  error_report()
          get_real_device_id()
              get_real_id()
                  error_report()
      assigned_device_pci_cap_init()
          check_irqchip_in_kernel()
              error_report()
          pci_add_capability()
          error_report()
      assigned_dev_register_msix_mmio()
          error_report()
      assigned_dev_register_regions()
          error_report()
      assign_device()
          error_report()
          assign_failed_examine()
              get_real_vendor_id()
                  get_real_id()
                      error_report()
              get_real_device_id()
                  get_real_id()
                      error_report()
              error_printf()
              error_report()
      assign_intx()
          check_irqchip_in_kernel()
              error_report()
          error_report()
          error_printf()

Laszlo Ersek (16):
  cutils: tighten qemu_parse_fd()
  monitor: add Error-propagating monitor_handle_fd_param2()
  pci-assign: accept Error from monitor_handle_fd_param2()
  pci-assign: make assign_failed_examine() just format the cause
  pci-assign: propagate errors from get_real_id()
  pci-assign: propagate Error from check_irqchip_in_kernel()
  pci: add Error-propagating pci_add_capability2()
  pci-assign: accept Error from pci_add_capability2()
  pci-assign: assignment should fail if we can't read config space
  pci-assign: propagate errors from get_real_device()
  pci-assign: propagate errors from assigned_device_pci_cap_init()
  pci-assign: propagate errors from assigned_dev_register_msix_mmio()
  pci-assign: propagate errors from assigned_dev_register_regions()
  pci-assign: propagate errors from assign_device()
  pci-assign: propagate errors from assign_intx()
  pci-assign: assigned_initfn(): set monitor error in common error
    handler

 include/hw/pci/pci.h      |   4 +
 include/monitor/monitor.h |   1 +
 hw/i386/kvm/pci-assign.c  | 273 ++++++++++++++++++++++++++++------------------
 hw/pci/pci.c              |  32 +++++-
 monitor.c                 |  29 ++++-
 util/cutils.c             |  13 ++-
 6 files changed, 232 insertions(+), 120 deletions(-)

-- 
1.8.3.1