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7d4c738c | 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 | |
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 | |
7d4c738c | 7 | hardware saves some memory plus the register sets of the boot CPU before the |
411ed322 MH |
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 | |
7d4c738c | 12 | a user space dump tool, which are loaded together into the saved memory region |
411ed322 MH |
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 | |
7d4c738c | 22 | register sets are stored in the prefix pages of the respective CPUs. To build a |
411ed322 | 23 | dump enabled kernel with the zcore driver, the kernel config option |
bf28a597 | 24 | CONFIG_CRASH_DUMP has to be set. When reading from "zcore/mem", the part of |
411ed322 MH |
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 | ||
7d4c738c MH |
29 | Since kernel version 3.12 also the /proc/vmcore file can also be used to access |
30 | the dump. | |
411ed322 | 31 | |
7d4c738c | 32 | To get a valid zfcpdump kernel configuration use "make zfcpdump_defconfig". |
411ed322 | 33 | |
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34 | The s390 zipl tool looks for the zfcpdump kernel and optional initrd/initramfs |
35 | under the following locations: | |
411ed322 | 36 | |
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37 | * kernel: <zfcpdump directory>/zfcpdump.image |
38 | * ramdisk: <zfcpdump directory>/zfcpdump.rd | |
411ed322 | 39 | |
7d4c738c | 40 | The zfcpdump directory is defined in the s390-tools package. |
411ed322 | 41 | |
7d4c738c MH |
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. | |
411ed322 | 45 | |
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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. | |
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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. |