Documentation/s390/zfcpdump.rst

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