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diff --git a/Documentation/s390/zfcpdump.rst b/Documentation/s390/zfcpdump.rst new file mode 100644 index 000000000..a61de7aa8 --- /dev/null +++ b/Documentation/s390/zfcpdump.rst @@ -0,0 +1,50 @@ +================================== +The s390 SCSI dump tool (zfcpdump) +================================== + +System z machines (z900 or higher) provide hardware support for creating system +dumps on SCSI disks. The dump process is initiated by booting a dump tool, which +has to create a dump of the current (probably crashed) Linux image. In order to +not overwrite memory of the crashed Linux with data of the dump tool, the +hardware saves some memory plus the register sets of the boot CPU before the +dump tool is loaded. There exists an SCLP hardware interface to obtain the saved +memory afterwards. Currently 32 MB are saved. + +This zfcpdump implementation consists of a Linux dump kernel together with +a user space dump tool, which are loaded together into the saved memory region +below 32 MB. zfcpdump is installed on a SCSI disk using zipl (as contained in +the s390-tools package) to make the device bootable. The operator of a Linux +system can then trigger a SCSI dump by booting the SCSI disk, where zfcpdump +resides on. + +The user space dump tool accesses the memory of the crashed system by means +of the /proc/vmcore interface. This interface exports the crashed system's +memory and registers in ELF core dump format. To access the memory which has +been saved by the hardware SCLP requests will be created at the time the data +is needed by /proc/vmcore. The tail part of the crashed systems memory which +has not been stashed by hardware can just be copied from real memory. + +To build a dump enabled kernel the kernel config option CONFIG_CRASH_DUMP +has to be set. + +To get a valid zfcpdump kernel configuration use "make zfcpdump_defconfig". + +The s390 zipl tool looks for the zfcpdump kernel and optional initrd/initramfs +under the following locations: + +* kernel: <zfcpdump directory>/zfcpdump.image +* ramdisk: <zfcpdump directory>/zfcpdump.rd + +The zfcpdump directory is defined in the s390-tools package. + +The user space application of zfcpdump can reside in an intitramfs or an +initrd. It can also be included in a built-in kernel initramfs. The application +reads from /proc/vmcore or zcore/mem and writes the system dump to a SCSI disk. + +The s390-tools package version 1.24.0 and above builds an external zfcpdump +initramfs with a user space application that writes the dump to a SCSI +partition. + +For more information on how to use zfcpdump refer to the s390 'Using the Dump +Tools' book, which is available from IBM Knowledge Center: +https://www.ibm.com/support/knowledgecenter/linuxonibm/liaaf/lnz_r_dt.html |