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