Based on kernel version 4.2. Page generated on 2015-09-09 12:14 EST.
1 The s390 SCSI dump tool (zfcpdump) 2 3 System z machines (z900 or higher) provide hardware support for creating system 4 dumps on SCSI disks. The dump process is initiated by booting a dump tool, which 5 has to create a dump of the current (probably crashed) Linux image. In order to 6 not overwrite memory of the crashed Linux with data of the dump tool, the 7 hardware saves some memory plus the register sets of the boot CPU before the 8 dump tool is loaded. There exists an SCLP hardware interface to obtain the saved 9 memory afterwards. Currently 32 MB are saved. 10 11 This zfcpdump implementation consists of a Linux dump kernel together with 12 a user space dump tool, which are loaded together into the saved memory region 13 below 32 MB. zfcpdump is installed on a SCSI disk using zipl (as contained in 14 the s390-tools package) to make the device bootable. The operator of a Linux 15 system can then trigger a SCSI dump by booting the SCSI disk, where zfcpdump 16 resides on. 17 18 The kernel part of zfcpdump is implemented as a debugfs file under "zcore/mem", 19 which exports memory and registers of the crashed Linux in an s390 20 standalone dump format. It can be used in the same way as e.g. /dev/mem. The 21 dump format defines a 4K header followed by plain uncompressed memory. The 22 register sets are stored in the prefix pages of the respective CPUs. To build a 23 dump enabled kernel with the zcore driver, the kernel config option 24 CONFIG_CRASH_DUMP has to be set. When reading from "zcore/mem", the part of 25 memory, which has been saved by hardware is read by the driver via the SCLP 26 hardware interface. The second part is just copied from the non overwritten real 27 memory. 28 29 Since kernel version 3.12 also the /proc/vmcore file can also be used to access 30 the dump. 31 32 To get a valid zfcpdump kernel configuration use "make zfcpdump_defconfig". 33 34 The s390 zipl tool looks for the zfcpdump kernel and optional initrd/initramfs 35 under the following locations: 36 37 * kernel: <zfcpdump directory>/zfcpdump.image 38 * ramdisk: <zfcpdump directory>/zfcpdump.rd 39 40 The zfcpdump directory is defined in the s390-tools package. 41 42 The user space application of zfcpdump can reside in an intitramfs or an 43 initrd. It can also be included in a built-in kernel initramfs. The application 44 reads from /proc/vmcore or zcore/mem and writes the system dump to a SCSI disk. 45 46 The s390-tools package version 1.24.0 and above builds an external zfcpdump 47 initramfs with a user space application that writes the dump to a SCSI 48 partition. 49 50 For more information on how to use zfcpdump refer to the s390 'Using the Dump 51 Tools book', which is available from 52 http://www.ibm.com/developerworks/linux/linux390.