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zfcpdump.txt

zfcpdump.txt 2.6 KB
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  1. The s390 SCSI dump tool (zfcpdump)
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  2. 

  3. System z machines (z900 or higher) provide hardware support for creating system
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  4. dumps on SCSI disks. The dump process is initiated by booting a dump tool, which
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  5. has to create a dump of the current (probably crashed) Linux image. In order to
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  6. not overwrite memory of the crashed Linux with data of the dump tool, the
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  7. hardware saves some memory plus the register sets of the boot CPU before the
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  8. dump tool is loaded. There exists an SCLP hardware interface to obtain the saved
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  9. memory afterwards. Currently 32 MB are saved.
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  10. 

  11. This zfcpdump implementation consists of a Linux dump kernel together with
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  12. a user space dump tool, which are loaded together into the saved memory region
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  13. below 32 MB. zfcpdump is installed on a SCSI disk using zipl (as contained in
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  14. the s390-tools package) to make the device bootable. The operator of a Linux
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  15. system can then trigger a SCSI dump by booting the SCSI disk, where zfcpdump
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  16. resides on.
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  17. 

  18. The kernel part of zfcpdump is implemented as a debugfs file under "zcore/mem",
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  19. which exports memory and registers of the crashed Linux in an s390
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  20. standalone dump format. It can be used in the same way as e.g. /dev/mem. The
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  21. dump format defines a 4K header followed by plain uncompressed memory. The
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  22. register sets are stored in the prefix pages of the respective CPUs. To build a
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  23. dump enabled kernel with the zcore driver, the kernel config option
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  24. CONFIG_CRASH_DUMP has to be set. When reading from "zcore/mem", the part of
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  25. memory, which has been saved by hardware is read by the driver via the SCLP
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  26. hardware interface. The second part is just copied from the non overwritten real
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  27. memory.
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  28. 

  29. Since kernel version 3.12 also the /proc/vmcore file can also be used to access
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  30. the dump.
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  31. 

  32. To get a valid zfcpdump kernel configuration use "make zfcpdump_defconfig".
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  33. 

  34. The s390 zipl tool looks for the zfcpdump kernel and optional initrd/initramfs
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  35. under the following locations:
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  36. 

  37. * kernel:  <zfcpdump directory>/zfcpdump.image
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  38. * ramdisk: <zfcpdump directory>/zfcpdump.rd
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  39. 

  40. The zfcpdump directory is defined in the s390-tools package.
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  41. 

  42. The user space application of zfcpdump can reside in an intitramfs or an
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  43. initrd. It can also be included in a built-in kernel initramfs. The application
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  44. reads from /proc/vmcore or zcore/mem and writes the system dump to a SCSI disk.
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  45. 

  46. The s390-tools package version 1.24.0 and above builds an external zfcpdump
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  47. initramfs with a user space application that writes the dump to a SCSI
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  48. partition.
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  49. 

  50. For more information on how to use zfcpdump refer to the s390 'Using the Dump
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  51. Tools book', which is available from
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  52. http://www.ibm.com/developerworks/linux/linux390.
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  53.