linux/Documentation/s390/zfcpdump.txt
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   1s390 SCSI dump tool (zfcpdump)
   2
   3System z machines (z900 or higher) provide hardware support for creating system
   4dumps on SCSI disks. The dump process is initiated by booting a dump tool, which
   5has to create a dump of the current (probably crashed) Linux image. In order to
   6not overwrite memory of the crashed Linux with data of the dump tool, the
   7hardware saves some memory plus the register sets of the boot cpu before the
   8dump tool is loaded. There exists an SCLP hardware interface to obtain the saved
   9memory afterwards. Currently 32 MB are saved.
  10
  11This zfcpdump implementation consists of a Linux dump kernel together with
  12a userspace dump tool, which are loaded together into the saved memory region
  13below 32 MB. zfcpdump is installed on a SCSI disk using zipl (as contained in
  14the s390-tools package) to make the device bootable. The operator of a Linux
  15system can then trigger a SCSI dump by booting the SCSI disk, where zfcpdump
  16resides on.
  17
  18The kernel part of zfcpdump is implemented as a debugfs file under "zcore/mem",
  19which exports memory and registers of the crashed Linux in an s390
  20standalone dump format. It can be used in the same way as e.g. /dev/mem. The
  21dump format defines a 4K header followed by plain uncompressed memory. The
  22register sets are stored in the prefix pages of the respective cpus. To build a
  23dump enabled kernel with the zcore driver, the kernel config option
  24CONFIG_ZFCPDUMP has to be set. When reading from "zcore/mem", the part of
  25memory, which has been saved by hardware is read by the driver via the SCLP
  26hardware interface. The second part is just copied from the non overwritten real
  27memory.
  28
  29The userspace application of zfcpdump can reside e.g. in an intitramfs or an
  30initrd. It reads from zcore/mem and writes the system dump to a file on a
  31SCSI disk.
  32
  33To build a zfcpdump kernel use the following settings in your kernel
  34configuration:
  35 * CONFIG_ZFCPDUMP=y
  36 * Enable ZFCP driver
  37 * Enable SCSI driver
  38 * Enable ext2 and ext3 filesystems
  39 * Disable as many features as possible to keep the kernel small.
  40   E.g. network support is not needed at all.
  41
  42To use the zfcpdump userspace application in an initramfs you have to do the
  43following:
  44
  45 * Copy the zfcpdump executable somewhere into your Linux tree.
  46   E.g. to "arch/s390/boot/zfcpdump. If you do not want to include
  47   shared libraries, compile the tool with the "-static" gcc option.
  48 * If you want to include e2fsck, add it to your source tree, too. The zfcpdump
  49   application attempts to start /sbin/e2fsck from the ramdisk.
  50 * Use an initramfs config file like the following:
  51
  52   dir /dev 755 0 0
  53   nod /dev/console 644 0 0 c 5 1
  54   nod /dev/null 644 0 0 c 1 3
  55   nod /dev/sda1 644 0 0 b 8 1
  56   nod /dev/sda2 644 0 0 b 8 2
  57   nod /dev/sda3 644 0 0 b 8 3
  58   nod /dev/sda4 644 0 0 b 8 4
  59   nod /dev/sda5 644 0 0 b 8 5
  60   nod /dev/sda6 644 0 0 b 8 6
  61   nod /dev/sda7 644 0 0 b 8 7
  62   nod /dev/sda8 644 0 0 b 8 8
  63   nod /dev/sda9 644 0 0 b 8 9
  64   nod /dev/sda10 644 0 0 b 8 10
  65   nod /dev/sda11 644 0 0 b 8 11
  66   nod /dev/sda12 644 0 0 b 8 12
  67   nod /dev/sda13 644 0 0 b 8 13
  68   nod /dev/sda14 644 0 0 b 8 14
  69   nod /dev/sda15 644 0 0 b 8 15
  70   file /init arch/s390/boot/zfcpdump 755 0 0
  71   file /sbin/e2fsck arch/s390/boot/e2fsck 755 0 0
  72   dir /proc 755 0 0
  73   dir /sys 755 0 0
  74   dir /mnt 755 0 0
  75   dir /sbin 755 0 0
  76
  77 * Issue "make image" to build the zfcpdump image with initramfs.
  78
  79In a Linux distribution the zfcpdump enabled kernel image must be copied to
  80/usr/share/zfcpdump/zfcpdump.image, where the s390 zipl tool is looking for the
  81dump kernel when preparing a SCSI dump disk.
  82
  83If you use a ramdisk copy it to "/usr/share/zfcpdump/zfcpdump.rd".
  84
  85For more information on how to use zfcpdump refer to the s390 'Using the Dump
  86Tools book', which is available from
  87http://www.ibm.com/developerworks/linux/linux390.
  88
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