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1 | s390 SCSI dump tool (zfcpdump) |
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 | |
7 | hardware saves some memory plus the register sets of the boot cpu before the | |
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 | |
12 | a userspace dump tool, which are loaded together into the saved memory region | |
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 | |
22 | register sets are stored in the prefix pages of the respective cpus. To build a | |
23 | dump enabled kernel with the zcore driver, the kernel config option | |
24 | CONFIG_ZFCPDUMP has to be set. When reading from "zcore/mem", the part of | |
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 | ||
29 | The userspace application of zfcpdump can reside e.g. in an intitramfs or an | |
30 | initrd. It reads from zcore/mem and writes the system dump to a file on a | |
31 | SCSI disk. | |
32 | ||
33 | To build a zfcpdump kernel use the following settings in your kernel | |
34 | configuration: | |
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 | ||
42 | To use the zfcpdump userspace application in an initramfs you have to do the | |
43 | following: | |
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 | ||
79 | In 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 | |
81 | dump kernel when preparing a SCSI dump disk. | |
82 | ||
83 | If you use a ramdisk copy it to "/usr/share/zfcpdump/zfcpdump.rd". | |
84 | ||
85 | For more information on how to use zfcpdump refer to the s390 'Using the Dump | |
86 | Tools book', which is available from | |
87 | http://www.ibm.com/developerworks/linux/linux390. |