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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. |
88 |
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