1*4882a593Smuzhiyun================================== 2*4882a593SmuzhiyunThe s390 SCSI dump tool (zfcpdump) 3*4882a593Smuzhiyun================================== 4*4882a593Smuzhiyun 5*4882a593SmuzhiyunSystem z machines (z900 or higher) provide hardware support for creating system 6*4882a593Smuzhiyundumps on SCSI disks. The dump process is initiated by booting a dump tool, which 7*4882a593Smuzhiyunhas to create a dump of the current (probably crashed) Linux image. In order to 8*4882a593Smuzhiyunnot overwrite memory of the crashed Linux with data of the dump tool, the 9*4882a593Smuzhiyunhardware saves some memory plus the register sets of the boot CPU before the 10*4882a593Smuzhiyundump tool is loaded. There exists an SCLP hardware interface to obtain the saved 11*4882a593Smuzhiyunmemory afterwards. Currently 32 MB are saved. 12*4882a593Smuzhiyun 13*4882a593SmuzhiyunThis zfcpdump implementation consists of a Linux dump kernel together with 14*4882a593Smuzhiyuna user space dump tool, which are loaded together into the saved memory region 15*4882a593Smuzhiyunbelow 32 MB. zfcpdump is installed on a SCSI disk using zipl (as contained in 16*4882a593Smuzhiyunthe s390-tools package) to make the device bootable. The operator of a Linux 17*4882a593Smuzhiyunsystem can then trigger a SCSI dump by booting the SCSI disk, where zfcpdump 18*4882a593Smuzhiyunresides on. 19*4882a593Smuzhiyun 20*4882a593SmuzhiyunThe user space dump tool accesses the memory of the crashed system by means 21*4882a593Smuzhiyunof the /proc/vmcore interface. This interface exports the crashed system's 22*4882a593Smuzhiyunmemory and registers in ELF core dump format. To access the memory which has 23*4882a593Smuzhiyunbeen saved by the hardware SCLP requests will be created at the time the data 24*4882a593Smuzhiyunis needed by /proc/vmcore. The tail part of the crashed systems memory which 25*4882a593Smuzhiyunhas not been stashed by hardware can just be copied from real memory. 26*4882a593Smuzhiyun 27*4882a593SmuzhiyunTo build a dump enabled kernel the kernel config option CONFIG_CRASH_DUMP 28*4882a593Smuzhiyunhas to be set. 29*4882a593Smuzhiyun 30*4882a593SmuzhiyunTo get a valid zfcpdump kernel configuration use "make zfcpdump_defconfig". 31*4882a593Smuzhiyun 32*4882a593SmuzhiyunThe s390 zipl tool looks for the zfcpdump kernel and optional initrd/initramfs 33*4882a593Smuzhiyununder the following locations: 34*4882a593Smuzhiyun 35*4882a593Smuzhiyun* kernel: <zfcpdump directory>/zfcpdump.image 36*4882a593Smuzhiyun* ramdisk: <zfcpdump directory>/zfcpdump.rd 37*4882a593Smuzhiyun 38*4882a593SmuzhiyunThe zfcpdump directory is defined in the s390-tools package. 39*4882a593Smuzhiyun 40*4882a593SmuzhiyunThe user space application of zfcpdump can reside in an intitramfs or an 41*4882a593Smuzhiyuninitrd. It can also be included in a built-in kernel initramfs. The application 42*4882a593Smuzhiyunreads from /proc/vmcore or zcore/mem and writes the system dump to a SCSI disk. 43*4882a593Smuzhiyun 44*4882a593SmuzhiyunThe s390-tools package version 1.24.0 and above builds an external zfcpdump 45*4882a593Smuzhiyuninitramfs with a user space application that writes the dump to a SCSI 46*4882a593Smuzhiyunpartition. 47*4882a593Smuzhiyun 48*4882a593SmuzhiyunFor more information on how to use zfcpdump refer to the s390 'Using the Dump 49*4882a593SmuzhiyunTools' book, which is available from IBM Knowledge Center: 50*4882a593Smuzhiyunhttps://www.ibm.com/support/knowledgecenter/linuxonibm/liaaf/lnz_r_dt.html 51