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| -rw-r--r-- | Documentation/s390/zfcpdump.txt | 87 |
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diff --git a/Documentation/s390/zfcpdump.txt b/Documentation/s390/zfcpdump.txt new file mode 100644 index 000000000000..cf45d27c4608 --- /dev/null +++ b/Documentation/s390/zfcpdump.txt @@ -0,0 +1,87 @@ +s390 SCSI dump tool (zfcpdump) + +System z machines (z900 or higher) provide hardware support for creating system +dumps on SCSI disks. The dump process is initiated by booting a dump tool, which +has to create a dump of the current (probably crashed) Linux image. In order to +not overwrite memory of the crashed Linux with data of the dump tool, the +hardware saves some memory plus the register sets of the boot cpu before the +dump tool is loaded. There exists an SCLP hardware interface to obtain the saved +memory afterwards. Currently 32 MB are saved. + +This zfcpdump implementation consists of a Linux dump kernel together with +a userspace dump tool, which are loaded together into the saved memory region +below 32 MB. zfcpdump is installed on a SCSI disk using zipl (as contained in +the s390-tools package) to make the device bootable. The operator of a Linux +system can then trigger a SCSI dump by booting the SCSI disk, where zfcpdump +resides on. + +The kernel part of zfcpdump is implemented as a debugfs file under "zcore/mem", +which exports memory and registers of the crashed Linux in an s390 +standalone dump format. It can be used in the same way as e.g. /dev/mem. The +dump format defines a 4K header followed by plain uncompressed memory. The +register sets are stored in the prefix pages of the respective cpus. To build a +dump enabled kernel with the zcore driver, the kernel config option +CONFIG_ZFCPDUMP has to be set. When reading from "zcore/mem", the part of +memory, which has been saved by hardware is read by the driver via the SCLP +hardware interface. The second part is just copied from the non overwritten real +memory. + +The userspace application of zfcpdump can reside e.g. in an intitramfs or an +initrd. It reads from zcore/mem and writes the system dump to a file on a +SCSI disk. + +To build a zfcpdump kernel use the following settings in your kernel +configuration: + * CONFIG_ZFCPDUMP=y + * Enable ZFCP driver + * Enable SCSI driver + * Enable ext2 and ext3 filesystems + * Disable as many features as possible to keep the kernel small. + E.g. network support is not needed at all. + +To use the zfcpdump userspace application in an initramfs you have to do the +following: + + * Copy the zfcpdump executable somewhere into your Linux tree. + E.g. to "arch/s390/boot/zfcpdump. If you do not want to include + shared libraries, compile the tool with the "-static" gcc option. + * If you want to include e2fsck, add it to your source tree, too. The zfcpdump + application attempts to start /sbin/e2fsck from the ramdisk. + * Use an initramfs config file like the following: + + dir /dev 755 0 0 + nod /dev/console 644 0 0 c 5 1 + nod /dev/null 644 0 0 c 1 3 + nod /dev/sda1 644 0 0 b 8 1 + nod /dev/sda2 644 0 0 b 8 2 + nod /dev/sda3 644 0 0 b 8 3 + nod /dev/sda4 644 0 0 b 8 4 + nod /dev/sda5 644 0 0 b 8 5 + nod /dev/sda6 644 0 0 b 8 6 + nod /dev/sda7 644 0 0 b 8 7 + nod /dev/sda8 644 0 0 b 8 8 + nod /dev/sda9 644 0 0 b 8 9 + nod /dev/sda10 644 0 0 b 8 10 + nod /dev/sda11 644 0 0 b 8 11 + nod /dev/sda12 644 0 0 b 8 12 + nod /dev/sda13 644 0 0 b 8 13 + nod /dev/sda14 644 0 0 b 8 14 + nod /dev/sda15 644 0 0 b 8 15 + file /init arch/s390/boot/zfcpdump 755 0 0 + file /sbin/e2fsck arch/s390/boot/e2fsck 755 0 0 + dir /proc 755 0 0 + dir /sys 755 0 0 + dir /mnt 755 0 0 + dir /sbin 755 0 0 + + * Issue "make image" to build the zfcpdump image with initramfs. + +In a Linux distribution the zfcpdump enabled kernel image must be copied to +/usr/share/zfcpdump/zfcpdump.image, where the s390 zipl tool is looking for the +dump kernel when preparing a SCSI dump disk. + +If you use a ramdisk copy it to "/usr/share/zfcpdump/zfcpdump.rd". + +For more information on how to use zfcpdump refer to the s390 'Using the Dump +Tools book', which is available from +http://www.ibm.com/developerworks/linux/linux390. |