The current discussions around uuids and mdev devices got me thinking, and I realized that the uuid is an interesting information for debugging devices. Currently, vfio-ccw does not really log any debug data (there's just a lone trace event). The common I/O layer has logged interesting information into the s390dbf for a long time; this has been very useful in the past, as the logged information can be accessed in a crash dump (e.g. by the crash tool). We cannot log directly into the common I/O layer debug features, though, as vfio-ccw may be a module. Another limitation is that for the sprintf-type debug feature, any string logged via '%s' must outlive the debug feature (as it is not copied for performance reasons). That means that logging the device name is right out, as devices may go away (the current common I/O layer code logs the numerical values of ssid/subchannel number instead); logging the uuid of an mdev device via %pU just works fine, though. My patch just logs some basics right now, we can certainly add more events. We should also think about adding more trace events: they may serve a similar purpose, especially if we should enhance the vfio code with trace events in the future (so that we can correlate those trace events with the vfio-ccw trace events, just as we can correlate the s390dbf events with the common I/O layer dbf events to get a more complete picture.) Cornelia Huck (1): vfio-ccw: add some logging drivers/s390/cio/vfio_ccw_drv.c | 50 ++++++++++++++++++++++++++-- drivers/s390/cio/vfio_ccw_fsm.c | 51 ++++++++++++++++++++++++++++- drivers/s390/cio/vfio_ccw_ops.c | 10 ++++++ drivers/s390/cio/vfio_ccw_private.h | 17 ++++++++++ 4 files changed, 124 insertions(+), 4 deletions(-) -- 2.20.1
