GTF builds an I/O summary record when an I/O interruption occurs and TRACE=IOX or TRACE=IOXP is a GTF option in effect. To trace PCI I/O interruptions, TRACE=PCI must also be in effect.
The I/O summary record will always contain a header section, followed by a section header and a common section. The section header describes the type and length of the following section and an indicator if this is the last section of the record.
A typical I/O summary record for a dasd device would have a header section, a common section, a data set section, a CMB section and, probably, one or more CCW sections. If an I/O summary record has to be extended the following extension records would consist of a header section with the header record number greater than 1, a common section and one or more CCW sections.